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PurposeThe purpose of this study is to propose a technique for delivering accurate doses in an image-guided system by developing an experimental setup optimized for total lymphoid irradiation (TLI) in rat lung transplantation.Materials and MethodsIn this study, a position-controlled shielding system was developed, and the dose was quantitatively evaluated using a 3D rat phantom and Gafchromic EBT3 film. In addition, we made our own image-guided system that allows the position of the rat and the shielding system to be confirmed during TLI.ResultsAs a result of using the position-controlled shielding system, it was found that the doses to the head and lungs were reduced by 93.1 and 87.4%, respectively, of the prescribed doses. In addition, it was shown that the position of the shielding system can be easily confirmed by using the image guidance system.ConclusionA shielding apparatus that can control dose delivery according to the size of the rat can optimize the dose for TLI in rat lung transplantation.

Introduction. COVID radiotherapy requires performance of all radiotherapy (RT) procedures during one site visit due to the infectious nature of the disease. The aim of the study was to develop methods of estimating the delivered dose based on electronic portal image device (EPID) signal during treatment. Material and methods. Electronic portal image device signal was measured as a function of the phantom dose. The dose in 14 COVID patients was estimated for two X6MV beams. Results. The method allows to estimate dose in phantom with uncertainty of 12%. In this case, a systematic error was reported. Therefore, coefficients for clinical data were calculated and used to determine the dose in patients. The mean difference between the dose calculated and the dose measured for the 14 patients was 1%, but the uncertainty of this method was estimated as ±6% Conclusions. The proposed method may be useful in clinical practice as in vivo method. However, due to high uncer- tainty, it should be dedicated to the detection of “big” errors. [ABSTRACT FROM AUTHOR]

Purpose/objective: In all treatment sites of our radiotherapy network, in vivo dosimetry (PerFRACTION™) was fully implemented in February 2018. We hypothesized that additional help with bladder and rectum preparation by home nursing would improve patients’ preparation and investigated if this could be assessed using in vivo dosimetry (IVD). Materials/methods: A retrospective study was conducted with a test group who received additional help with bladder and rectum preparation by home nurses and a control group who only received information on bladder and rectum preparation according to the standard protocol. Patients were treated with a 6 MV Volumetric Modulated Arc Therapy (VMAT) technique. Electronic portal imaging device (EPID)-based integrated transit dose images were acquired on the first 3 days of treatment and weekly thereafter or more if failed fractions (FF) occurred. Results were analyzed using a global gamma analysis with a threshold of 20%, tolerance of 5% (dose difference) and 5 mm (distance to agreement), and a passing level of 95%. Results: Data of 462 prostate patients was analyzed: 39 and 423 in a test and control group respectively with a comparable number of measurements (on average 8.0 (σ = 4.8) and 7.1 (σ = 4.5) respectively per treatment course). Of the FF, 39% and 31% were related to variations in bladder and rectum filling for the test and control group respectively. Subgroups were created based on the number of FF, no statistically significant differences were observed. Conclusion: Two dimensional EPID-based IVD successfully detected deviations due to variations in bladder and rectum filling, however it could not confirm the hypothesis.

Brachytherapy can deliver high doses to the target while sparing healthy tissues due to its steep dose gradient leading to excellent clinical outcome. Treatment accuracy depends on several manual steps making brachytherapy susceptible to operational mistakes. Currently, treatment delivery verification is not routinely available and has led, in some cases, to systematic errors going unnoticed for years. The brachytherapy community promoted developments in in vivo dosimetry (IVD) through research groups and small companies. Although very few of the systems have been used clinically, it was demonstrated that the likelihood of detecting deviations from the treatment plan increases significantly with time-resolved methods. Time–resolved methods could interrupt a treatment avoiding gross errors which is not possible with time-integrated dosimetry. In addition, lower experimental uncertainties can be achieved by using source-tracking instead of direct dose measurements. However, the detector position in relation to the patient anatomy remains a main source of uncertainty. The next steps towards clinical implementation will require clinical trials and systematic reporting of errors and near-misses. It is of utmost importance for each IVD system that its sensitivity to different types of errors is well understood, so that end-users can select the most suitable method for their needs. This report aims to formulate requirements for the stakeholders (clinics, vendors, and researchers) to facilitate increased clinical use of IVD in brachytherapy. The report focuses on high dose-rate IVD in brachytherapy providing an overview and outlining the need for further development and research.

External beam radiotherapy with photon beams is a highly accurate treatment modality, but requires extensive quality assurance programs to confirm that radiation therapy will be or was administered appropriately. In vivo dosimetry (IVD) is an essential element of modern radiation therapy because it provides the ability to catch treatment delivery errors, assist in treatment adaptation, and record the actual dose delivered to the patient. However, for various reasons, its clinical implementation has been slow and limited. The purpose of this report is to stimulate the wider use of IVD for external beam radiotherapy, and in particular of systems using electronic portal imaging devices (EPIDs). After documenting the current IVD methods, this report provides detailed software, hardware and system requirements for in vivo EPID dosimetry systems in order to help in bridging the current vendor-user gap. The report also outlines directions for further development and research. In vivo EPID dosimetry vendors, in collaboration with users across multiple institutions, are requested to improve the understanding and reduce the uncertainties of the system and to help in the determination of optimal action limits for error detection. Finally, the report recommends that automation of all aspects of IVD is needed to help facilitate clinical adoption, including automation of image acquisition, analysis, result interpretation, and reporting/documentation. With the guidance of this report, it is hoped that widespread clinical use of IVD will be significantly accelerated.

Background: Intracavitary brachytherapy plays a major role in management of cervical carcinoma. Assessment of dose received by OAR’s therefore becomes crucial for the estimation of radiation toxicities in HDR brachytherapy. Objective: Purpose of this study is to evaluate the role of in vivo dosimetry in HDR brachytherapy and to compare actual doses delivered to OAR’ s with those calculated during treatment planning. Material and Methods: In this retrospective study, 50 patients of cervical carcinoma were treated by Microselectron HDR. Out of 50 patients, 26 were treated with a dose of 7 Gy and 24 with a dose of 9 Gy, prescribed to point A. Brachytherapy planning and evaluation of dose to bladder and rectum was done on TPS & in vivo dosimetry was performed using portable MOSFET. Results: Calibration factors calculated for both dosimeters are almost equal and are 0.984 cGy/mV and 1.0895 cGy/mV. For bladder, dose deviation was found to be within ± 5% in 28 patients, ± 5-10% in 14 patients, ± 10-15% in 4 patients. Deviation between TPS-calculated dose and dose measured by MOSFET for rectum was within ± 5% in 31 patients, ± 5–10% in 8 patients, and ± 10–15% in 7 patients. Conclusion: TPS calculated doses were slightly higher than that measured by MOSFET. The use of small size MOSFET dosimeter is an efficient method for accurately measuring doses in high-dose gradient fields typically seen in brachytherapy. Therefore, to reduce the risk of large errors in dose delivery, in vivo dosimetry can be done in addition to TPS computations.

Surface brachytherapy (BT) lacks standard quality assurance (QA) protocols. Commercially available treatment planning systems (TPSs) are based on a dose calculation formalism that assumes the patient is made of water, resulting in potential deviations between planned and delivered doses. Here, a method for treatment plan verification for skin surface BT is reported. Chips of thermoluminescent dosimeters (TLDs) were used for dose point measurements. High-dose-rate treatments were simulated and delivered through a custom-flap applicator provided with four fixed catheters to guide the Iridium-192 (Ir-192) source by way of a remote afterloading system. A flat water-equivalent phantom was used to simulate patient skin. Elekta TPS Oncentra Brachy was used for planning. TLDs were calibrated to Ir-192 through an indirect method of linear interpolation between calibration factors (CFs) measured for 250 kV X-rays, Cesium-137, and Cobalt-60. Subsequently, plans were designed and delivered to test the reproducibility of the irradiation set-up and to make comparisons between planned and delivered dose. The obtained CF for Ir-192 was (4.96 ± 0.25) μC/Gy. Deviations between measured and TPS calculated doses for multi-catheter treatment configuration ranged from −8.4% to 13.3% with an average of 0.6%. TLDs could be included in clinical practice for QA in skin BT with a customized flap applicator.

Background: In vivo dosimetry (IVD) is rarely performed in brachytherapy (BT), allowing potential dose misadministration to go unnoticed. This study presents a clinical routine-calibration method of detectors for IVD in high (HDR) and pulsed dose rate (PDR) Ir-192 BT., Purpose: To evaluate the dosimetric precision and feasibility of an in-clinic calibration routine of detectors for IVD in afterloading BT., Methods: Calibrations were performed in a PMMA phantom with two needles inserted 20 mm apart. The source was loaded in one of the needles at 15 dwells for 10 s. The detector was placed in the other needle, and its signal was recorded. The mean signal at each dwell position was fitted to the expected dose rate with the calibration factor and the detector's longitudinal position being free parameters. The method was tested with an inorganic scintillation detector using one Ir-192 FlexiSource HDR and two Ir-192 GammaMedPlus PDR sources and followed by validation measurements in water., Results: The standard measurement uncertainty (k = 1) of the calibration factor in absolute terms (Gy/s) was 3.2/3.4% for the HDR/PDR source. The uncertainty was dominated by source strength uncertainty, and the precision of the method was <1%. The mean ± 1SD of the difference in measured and expected dose rate during validation was 1.5 ± 4.7% (HDR) and 0.0 ± 4.1% (PDR) with a positional uncertainty in the setup of 0.33/0.23 mm (HDR/PDR) (k = 1)., Conclusion: A precise and feasible in-clinic calibration method for IVD and source strength consistency tests in BT was presented., (Copyright © 2024 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

Purpose: A high level of personalization in Molecular Radiotherapy (MRT) could bring advantages in terms of treatment effectiveness and toxicity reduction. Individual organ‐level dosimetry is crucial to describe the radiopharmaceutical biodistribution expressed by the patient, to estimate absorbed doses to normal organs and target tissue(s). This paper presents a proof‐of‐concept Monte Carlo simulation study of "WIDMApp" (Wearable Individual Dose Monitoring Apparatus), a multi‐channel radiation detector and data processing system for in vivo patient measurement and collection of radiopharmaceutical biokinetic data (i.e., time‐activity data). Potentially, such a system can increase the amount of such data that can be collected while reducing the need to derive it via nuclear medicine imaging. Methods: a male anthropomorphic MIRD phantom was used to simulate photons (i.e., gamma‐rays) propagation in a patient undergoing a 131I thyroid treatment. The administered activity was set to the amount usually administered for the treatment of differentiated carcinoma while its initial distribution in different organs was assigned following the ICRP indications for the 131I biokinetics. Using this information, the simulation computes the Time‐dependent Counts Curves (TCCs) that would have been measured by seven WIDMApp‐like sensors placed and oriented to face each one of five emitting organs plus two thyroid lobes. A deconvolution algorithm was then applied on this simulated data set to reconstruct the Time‐Activity Curve (TAC) of each organ. Deviations of the reconstructed TACs parameters from values used to generate them were studied as a function of the deconvolution algorithm initialization parameters and assuming non‐Poisson fluctuation of the TCCs data points. Results: This study demonstrates that it is possible, at least in the simple simulated scenario, to reconstruct the organ cumulated activity by measuring the time dependence of counts recorded by several detectors placed at selected positions on the patient's body. The ability to perform in vivo sampling more frequently than conventional biokinetic studies increases the number of time points and therefore the accuracy in TAC estimates. In this study, an accuracy on cumulated activity of 5% is obtained even with a 20% error on the TCC data points and a 50% error on the initial guess on the parameters of the deconvolution algorithm. Conclusions: the WIDMApp approach could provide an effective tool to characterize more accurately the radiopharmaceutical biokinetics in MRT patients, reducing the need of resources of nuclear medicine departments, such as technologist and scanner time, to perform individualized biokinetics studies. The relatively simple hardware for the approach proposed would allow its application to large numbers of patients. The results obtained justify development of an actual prototype system to characterize this technique under realistic conditions. [ABSTRACT FROM AUTHOR]

Aim: This study reveals the characteristic nature and the use of optically stimulated luminescence dosimeters (OSLD) as an in vivo dosimetry tool for head and neck intensity-modulated radiation therapy (IMRT). Materials and methods: Calibration and characterisation of OSLD such as sensitivity, reproducibility, dose-rate dependence, beam quality dependence, output factor measurement and comparison of two bleaching techniques using halogen and compact fluorescent lamp (CFL) were initially performed. Later, eye dose measurements were performed for head and neck IMRT patients using OSLD and were compared with the corresponding dose calculated by the treatment planning system (TPS). Results: While the sensitivity was found to be within ±5%, the dose-rate dependence and reproducibility were found to be within ±3%. The OSLD showed an under-response of 3% for 15 MV and an increase in response by 5% for Co60 (1·25 MeV) when compared with the 6 MV X-ray beam. Therefore, a separate calibration for different beam energies is required. The percentage deviation of OSLD to that of TPS was found to be within ±2·77%. The OSLD has been successfully used for the in vivo dosimetry of patients who received IMRT. Hence, it is concluded that OSLDs can serve as effective dosimeters for in vivo dosimetry. [ABSTRACT FROM AUTHOR]

Featured Application: Transit dosimetry, with Electronic Portal Imaging Device (EPID), is a powerful tool for in vivo dosimetry (IVD). Despite its wide availability and its simplicity of use, the clinical implementation of such a dosimetric technique is still challenging. One reason for the difficulty of IVD implementation is the lack of guidelines around the validation and acceptance of EPID IVD algorithms. In this paper we propose an evaluation method for assessing the accuracy of a novel 3D EPID back-projection algorithm for IVD. To the best of our knowledge, the EPID back-projection algorithms have never been validated in anthropomorphic phantom against direct two-dimensional measurements, and the new algorithm, introduced in version 5.8 of the Dosimetry Check software for dealing with tissue inhomogeneity, has never been evaluated before. The aim of this study was to develop and apply an evaluation method for assessing the accuracy of a novel 3D EPID back-projection algorithm for in vivo dosimetry. The novel algorithm of Dosimetry Check (DC) 5.8 was evaluated. A slab phantom homogeneously filled, or with air and bone inserts, was used for fluence reconstruction of different squared fields. VMAT plans in different anatomical sites were delivered on an anthropomorphic phantom. Dose distributions were measured with radiochromic films. The 2D Gamma Agreement Index (GAI) between the DC and the film dose distributions (3%, 3 mm) was computed for assessing the accuracy of the algorithm. GAIs between films and TPS and between DC and TPS were also computed. The fluence reconstruction accuracy was within 2% for all squared fields in the three slabs' configurations. The GAI between the DC and the film was 92.7% in the prostate, 92.9% in the lung, 96.6% in the head and the neck, and 94.6% in the brain. An evaluation method for assessing the accuracy of a novel EPID algorithm was developed. The DC algorithm was shown to be able to accurately reconstruct doses in all anatomic sites, including the lung. The methodology described in the present study can be applied to any EPID back-projection in vivo algorithm. [ABSTRACT FROM AUTHOR]

Purpose: High‐dose rate (HDR) and pulsed‐dose rate (PDR) brachytherapy would benefit from an independent treatment verification system to monitor treatment delivery and to detect errors in real time. This paper characterizes and provides an uncertainty budget for a detector based on a fiber‐coupled high‐Z inorganic scintillator capable of performing time‐resolved in vivo dosimetry during HDR and PDR brachytherapy. Method: The detector was composed of a detector probe and an optical reader. The detector probe consisted of either a 0.5 × 0.4 × 0.4 mm3 (HDR) or a 1.0 × 0.4 × 0.4 mm3 (PDR) cuboid ZnSe:O crystal glued onto an optical‐fiber cable. The outer diameter of the detector probes was 1 mm, and fit inside standard brachytherapy catheters. The signal from the detector probe was read out at 20 Hz by a photodiode and a data acquisition device inside the optical reader. In order to construct an uncertainty budget for the detector, six characteristics were determined: (1) temperature dependence of the detector probe, (2) energy dependence as a function of the probe‐to‐source position in 2D (determined with 2 mm resolution using a robotic arm), (3) the signal‐to‐noise ratio (SNR), (4) short‐term stability over 8 h, and (5) long‐term stability of three optical readers and four probes used for in vivo monitoring in HDR and PDR treatments over 21 months (196 treatments and 189 detector calibrations, and (6) dose‐rate dependence. Results: The total uncertainty of the detector at a 20 mm probe‐to‐source distance was < 5.1% and < 5.8% for the HDR and PDR versions, respectively. Regarding the above characteristics, (1) the sensitivity of the detector decreased by an average of 1.4%/°C for detector probe temperatures varying from 22 to 37°C; (2) the energy dependence of the detector was nonlinear and depended on both probe‐to‐source distance and the angle between the probe and the brachytherapy source; (3) the median SNRs were 187 and 34 at a 20 mm probe‐to‐source distance for the HDR and PDR versions, respectively (corresponding median source activities of 4.8 and 0.56 Ci, respectively); (4) the detector response varied by 0.6% in 11 identical irradiations over 8 h; (5) the sensitivity of the four detector probes decreased systematically by 0–1.2%/100 Gy of dose delivered to the probes, and random fluctuations of 4.8% in the sensitivity were observed for the three probes used in PDR and 1.9% for the probe used in HDR; and (6) the detector response was linear with dose rate. Conclusion: ZnSe:O detectors can be used effectively for in vivo dosimetry and with high accuracy for HDR and PDR brachytherapy applications. [ABSTRACT FROM AUTHOR]

Purpose: Electron‐based ultra‐high dose rate radiation therapy (UHDR‐RT), also known as Flash‐RT, has shown the ability to improve the therapeutic index in comparison to conventional radiotherapy (CONV‐RT) through increased sparing of normal tissue. However, the extremely high dose rates in UHDR‐RT have raised the need for accurate real‐time dosimetry tools. This work aims to demonstrate the potential of the emerging technology of Ionized Radiation Acoustic Imaging (iRAI) through simulation studies and investigate its characteristics as a promising relative in vivo dosimetric tool for UHDR‐RT. Methods: The detection of induced acoustic waves following a single UHDR pulse of a modified 6 MeV 21EX Varian Clinac in a uniform porcine gelatin phantom that is brain‐tissue equivalent was simulated for an ideal ultrasound transducer. The full 3D dose distributions in the phantom for a 1 × 1 cm2 field were simulated using EGSnrc (BEAMnrc∖DOSXYZnrc) Monte Carlo (MC) codes. The relative dosimetry simulations were verified with dose experimental measurements using Gafchromic films. The spatial dose distribution was converted into an initial pressure source spatial distribution using the medium‐dependent dose–pressure relation. The MATLAB‐based toolbox k‐Wave was then used to model the propagation of acoustic waves through the phantom and perform time‐reversal (TR)‐based imaging reconstruction. The effect of the various linear accelerator (linac) operating parameters, including linac pulse duration and pulse repetition rate (frequency), were investigated as well. Results: The MC dose simulation results agreed with the film measurement results, specifically at the central beam region up to 80% dose within approximately 5% relative error for the central profile region and a local relative error of <6% for percentage dose depth. IRAI‐based FWHM of the radiation beam was within approximately 3 mm relative to the MC‐simulated beam FWHM at the beam entrance. The real‐time pressure signal change agreed with the dose changes proving the capability of the iRAI for predicting the beam position. IRAI was tested through 3D simulations of its response to be based on the temporal changes in the linac operating parameters on a dose per pulse basis as expected theoretically from the pressure‐dose proportionality. The pressure signal amplitude obtained through 2D simulations was proportional to the dose per pulse. The instantaneous pressure signal amplitude decreases as the linac pulse duration increases, as predicted from the pressure wave generation equations, such that the shorter the linac pulse the higher the signal and the better the temporal (spatial) resolutions of iRAI. The effect of the longer linac pulse duration on the spatial resolution of the 3D constructed iRAI images was corrected for linac pulse deconvolution. This correction has improved the passing rate of the 1%/1 mm gamma test criteria, between the pressure‐constructed and dosimetric beam characteristics, to as high as 98%. Conclusions: A full simulation workflow was developed for testing the effectiveness of iRAI as a promising relative dosimetry tool for UHDR‐RT radiation therapy. IRAI has shown the advantage of 3D dose mapping through the dose signal linearity and, hence, has the potential to be a useful dosimeter at depth dose measurement and beam localization and, hence, potentially for in vivo dosimetry in UHDR‐RT. [ABSTRACT FROM AUTHOR]

Intracavitary cervical brachytherapy delivers high doses of radiation to the target tissue and a portion of these doses will also hit the rectal organs due to their close proximity. Rectal dose can be evaluated from dosimetric parameters in the treatment planning system (TPS) and in vivo (IV) dose measurement. This study analyzed the correlation between IV rectal dose with selected volume and point dose parameters from TPS. A total of 48 insertions were performed and IV dose was measured using the commercial PTW 9112 semiconductor diode probe. In 18 of 48 insertions, a single MOSkin detector was attached on the probe surface at 50 mm from the tip. Four rectal dosimetric parameters were retrospectively collected from TPS; (a) PTW 9112 diode maximum reported dose (RPmax) and MOSkin detector, (b) minimum dose to 2 cc (D2cc), (c) ICRU reference point (ICRUr), and (d) maximum dose from additional points (Rmax). The IV doses from both detectors were analyzed for correlation with these dosimetric parameters. This study found a significantly high correlation between IV measured dose from RPmax (r = 0.916) and MOSkin (r = 0.959) with TPS planned dose. The correlation between measured RPmax with both D2cc and Rmax revealed high correlation of r > 0.7, whereas moderate correlation (r = 0.525) was observed with ICRUr. There was no significant correlation between MOSkin IV measured dose with D2cc, ICRUr and Rmax. The non-significant correlation between parameters was ascribable to differences in both detector position within patients, and dosimetric volume and point location determined on TPS, rather than detector uncertainties. [ABSTRACT FROM AUTHOR]

Purpose: We aimed to develop a disposable rectum dosimeter and to demonstrate its ability to measure exposure dose to the rectum during brachytherapy for cervical cancer treatment using high‐dose rate 192Ir. Our rectum dosimeter measures the dose with an optically stimulated luminescence (OSL) sheet which was furled to a catheter. The catheter we used is 6 mm in diameter; therefore, it is much less invasive than other rectum dosimeters. The rectum dosimeter developed in this study has the characteristics of being inexpensive and disposable. It is also an easy‐to‐use detector that can be individually sterilized, making it suitable for clinical use. Methods: To obtain a dose calibration curve, phantom experiments were performed. Irradiation was performed using a cubical acrylic phantom, and the response of the OSL dosimeter was calibrated with the calculation value predicted by the treatment planning system (TPS). Additionally, the dependence of catheter angle on the dosimeter position and repeatability were evaluated. We also measured the absorbed dose to the rectum of patients who were undergoing brachytherapy for cervical cancer (n = 64). The doses measured with our dosimeters were compared with the doses calculated by the TPS. In order to examine the causes of large differences between measured and planned doses, we classified the data into common and specific cases when performing this clinical study. For specific cases, the following three categories were considered: (a) patient movement, (b) gas in the vagina and/or rectum, and (c) artifacts in the X‐ray image caused by applicators. Results: A dose calibration curve was obtained in the range of 0.1 Gy–10.0 Gy. From the evaluation of the dependence of catheter angle on the dosimeter position and repeatability, we determined that our dosimeter can measure rectum dose with an accuracy of 3.1% (k = 1). In this clinical study, we succeeded in measuring actual doses using our rectum dosimeter. We found that the deviation of the measured dose from the planned dose was derived to be 12.7% (k = 1); this result shows that the clinical study included large elements of uncertainty. The discrepancies were found to be due to patient motion during treatment, applicator movement after planning images were taken, and artifacts in the planning images. Conclusions: We present the idea that a minimally invasive rectum dosimeter can be fabricated using an OSL sheet. Our clinical study demonstrates that a rectum dosimeter made from an OSL sheet has sufficient ability to evaluate rectum dose. Using this dosimeter, valuable information concerning organs at risk can be obtained during brachytherapy. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study is to estimate delivered radiation doses inside planning tumor volume (PTV) using the in vivo (mid-plane dose) measurement and transit measurement methods in gynecological malignancy patients undergoing three-dimensional conformal radiotherapy (3DCRT) using calibrated ionization chambers. Materials and Methods: Six patients with histopathologically proven carcinoma of the cervix or endometrium were planned with four-field 3DCRT to the pelvic site. Isocenter was at the geometric mid-plane of PTV with a dose prescription of 50 Gy in 25 fractions. Clinical mid-plane dose (Diso,Transit) estimates were done in one method (transit) using the FC-65 positioned at electronic portal imaging device level. In another method, a repeat computerized tomography scan was performed (at the 11th fraction) using CC-13 having a protective cap in the vaginal cavity for in vivo measurements (Din vivo). Simultaneous measurements were performed with the two chambers from the 11th fraction onward at least 3–4 times during the remaining course of treatment. Results: The agreement of mean doses from these two described methods and treatment planning system reference doses was in the range of −4.4 ± 1.1% (minimum) to −0.3 ± 2.0% (maximum) and −4.0 ± 1.7% (minimum) to 1.9 ± 2.4% for Dinvivoand Diso,Transit, respectively, which are an acceptable range of daily radiation dose delivery. Conclusion: The fundamental importance of this study lies in simultaneous validation of delivered dose in real time with two methods. A study in this small number of patients has given the confidence to apply transit measurements for quality assurance on a routine basis as an accepted clinical dosimetry for the selected patients.

Introduction: One of the useful standard quality assurance techniques in radiation therapy is monitoring entrance doses in in-vivo dosimetry. An overall tolerance limit of 5% of the absorbed radiation dose has been recommended by the International Commission of Radiological Units. The implementation of an in vivo dosimetry still remains as a challenge to clinical medical physicists. As a result, the practice of constant monitoring of patients undergoing radiation therapy in most of the radiotherapy departments in Africa has not been given much attention. The study aimed at the evaluation of in-vivo entrance dosimetry using diodes to verify the accuracy of the radiation delivered to patients, compared to prescribed doses. Material and Methods: In this paper, a protocol for in vivo dosimetry using a two flat surface Sun Nuclear Corporation diode in a radiotherapy department has been implemented in equinox Cobalt 60 beams. A water phantom calibrated was performed using the International Atomic Energy Agency standards (TRS 398). Calibration coefficients were determined with diodes using a Perspex phantom to derive correction factors. A total number of 137 patients’ doses were measured with the diodes during the treatment of 4 different sites. Results: The average deviation between the measured and expected entrance dose performed by the phantom studies was 5% (0.34±1.8%) in almost all cases. Conclusion: The developed protocol in this study indicates that in vivo dosimetry using silicon diodes is reliable, which can be adopted as a universal quality assurance tool in the radiotherapy departments. Moreover, measurements with diodes can be acquired online which produces an instant readout and is relatively cheaper as compared to the ion chamber.

Purpose: There is an increased interest in using non‐coplanar beams for radiotherapy, including SBRT and SRS. This approach can significantly reduce doses to organs‐at‐risk, however, it requires stringent quality assurance, especially when a dynamic treatment couch is used. In this work, new functionality that allows using non‐coplanar beam arrangements in addition to conventional coplanar beams was added and validated to the previously developed in vivo dose verification system. Methods: The existing program code was modified to manage the additional treatment couch parameters: angle and positions. Ten non‐coplanar test plans that use a static couch were created in the treatment planning system. Also, two plans that use a dynamic treatment couch were created and delivered using Varian Developer mode, since the treatment planning system does not support a dynamic couch. All non‐coplanar test trajectories were delivered on a simple geometric phantom, using an Edge linear accelerator (Varian Medical Systems) with the megavoltage imager deployed and acquiring megavoltage transmission images that were used to calculate the delivered 3D dose distributions in the phantom with the updated dose calculation algorithm. The reconstructed dose distributions were compared using the 3D chi‐comparison test with 2%/2mm tolerances to the corresponding reference dose distributions obtained from the treatment planning system. Results: The chi‐comparison test resulted in at least a 97.0% pass rate over the entire 3D volume for all tested trajectories. For static gantry, static couch non‐coplanar fields, and non‐coplanar arcs using dynamic couch the pass rates observed were at least 98%, while for the static couch, non‐transverse coplanar arc fields, pass rates were at least 97%. Conclusions: A model‐based 3D dose calculation algorithm has been extended and validated for a variety of non‐coplanar beam trajectories of different complexities. This system can potentially be applied for quality assurance of treatment delivery systems that use complex, non‐coplanar beam arrangements. [ABSTRACT FROM AUTHOR]

Background: The main goal of radiation therapy is to deliver the highest dose to the tumor and at the same time the lowest dose to the surrounding normal tissue. In vivo dosimetry is a quality control procedure that, instead of controlling the components separately, directly examines the dose reached to the tumor area. Objectives: In this study, the entrance, exit, and middle dose of the breast and supraclavicular area of patients with breast cancer under radiation therapy were measured and compared with calculations. Methods: In this experimental study, the entrance and exit doses of 33 patients with breast tumors treated with 6 MV and 18MV photons were measured simultaneously. The measurement was done, using p-type diodes after calibration and, then, the midpoint dose was calculated, using the transfer method and arithmetic mean method. Also, the entrance dose, exit dose, and midline dose measured with dosimeter were compared with the calculated values in the treatment planning system. Results: There was no significant difference between calculated and measured doses in the entrance, exit, and midline point in breast regions (P> 0.05), but in the supraclavicular region, a challenge was observed. The difference in entrance and midline point between calculation and measurement is not significant based on the transfer method, but there is a significant error based on the arithmetic mean method (P < 0.05). Conclusions: In vivo dosimetry by measured real given dose to the patient can perform a basic role in the quality control of the radiotherapy department. It seems in the entrance dose, the relative error is smaller but due to the smaller value of exit dose, the relative error in small values is more apparent. [ABSTRACT FROM AUTHOR]

Purpose: To report on the accuracy of an in vivo dosimetry (IVD)‐based source tracking (ST) method for high dose rate (HDR) prostate brachytherapy (BT). Methods: The ST was performed on a needle‐by‐needle basis. A least square fit of the expected to the measured dose rate was performed using the active dwell positions in the given needle. Two fitting parameters were used to determine the position of each needle relative to the IVD detector: radial (away or toward the detector) and longitudinal (along the axis of the treatment needle). The accuracy of the ST was assessed in a phantom where the geometries of five HDR prostate BT treatments previously treated at our clinic were reproduced. For each of the five treatment geometries, one irradiation was performed with the detector placed in the middle of the implant. Furthermore, four additional irradiations were performed for one of the geometries where the detector was retracted caudally in four steps of 10–15 mm and up to 12 mm inferior of the most inferior active dwell position, which represented the prostate apex. The time resolved dose measurements were retrieved at a rate of 20 Hz using a detector based on an Al2O3:C radioluminescence crystal, which was placed inside a standard BT needle. Individual calibrations of the detector were performed prior to each of the nine irradiations. Results: Source tracking could be applied in all needles across all nine irradiations. For irradiations with the detector located in the middle region of the implant (a total of 89 needles), the mean ± standard deviation (SD, k = 1) accuracy was −0.01 mm ± 0.38 mm and 0.30 mm ± 0.38 mm in the radial and longitudinal directions, respectively. Caudal retraction of the detector did not lead to reduced accuracy as long as the detector was located superior to the most inferior active dwell positions in all needles. However, reduced accuracy was observed for detector positions inferior to the most inferior active dwell positions which corresponded to detector positions in and inferior to the prostate apex region. Detector positions in the prostate apex and 12 mm inferior to the prostate resulted in mean ± SD (k = 1) ST accuracy of 0.7 mm ± 1 mm and 2.8 mm ± 1.6 mm, respectively, in radial direction, and −1.7 mm ± 1 mm and −2.1 mm ± 1.1 mm, respectively, in longitudinal direction. The largest deviations for the configurations with those detector positions were 2.6 and 5.4 mm, respectively, in the radial direction and −3.5 and −3.8 mm, respectively, in the longitudinal direction. Conclusion: This phantom study demonstrates that ST based on IVD during prostate BT is adequately accurate for clinical use. The ST yields submillimeter accuracy on needle positions as long as the IVD detector is positioned superior to at least one active dwell position in all needles. Locations of the detector inferior to the prostate apex result in decreased ST accuracy while detector locations in the apex region and above are advantageous for clinical applications. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study is to perform three‐dimensional (3D) source position reconstruction by combining in vivo dosimetry measurements from two independent detector systems. Methods: Time‐resolved dosimetry was performed in a water phantom during HDR brachytherapy irradiation with 192Ir source using two detector systems. The first was based on three plastic scintillator detectors and the second on a single inorganic crystal (CsI:Tl). Brachytherapy treatments were simulated in water under TG‐43U1 conditions, including a HDR prostate plan. Treatment needles were placed in distances covering a range of source movement of 120 mm around the detectors. The distance from each dwell position to each scintillator was determined based on the measured dose rates. The three distances given by the mPSD were recalculated to a position along the catheter (z) and a distance radially away from the mPSD (xy) for each dwell position (a circumference around the mPSD). The source x, y, and z coordinates were derived from the intersection of the mPSD's circumference with the sphere around the ISD based on the distance to this detector. We evaluated the accuracy of the source position reconstruction as a function of the distance to the source, the most likely location for detector positioning within a prostate volume, as well as the capacity to detect positioning errors. Results: Approximately 4000 source dwell positions were tracked for eight different HDR plans. An intersection of the mPSD torus and the ISD sphere was observed in 77.2% of the dwell positions, assuming no uncertainty in the dose rate determined distance. This increased to 100% if 1σ search regions were added. However, only 73(96)% of the expected dwell positions were found within the intersection band for 1(2) σ uncertainties. The agreement between the source's reconstructed and expected positions was within 3 mm for a range of distances to the source up to 50 mm. The experiments on a HDR prostate plan, showed that by having at least one of the detectors located in the middle of the prostate volume, reduces the measurement deviations considerably compared to scenarios where the detectors were located outside of the prostate volume. The analysis showed a detection probability that, in most cases, is far from the random detection threshold. Errors of 1(2) mm can be detected in ranges of 5–25 (25–50) mm from the source, with a true detection probability rate higher than 80%, while the false probability rate is kept below 20%. Conclusions: By combining two detector responses, we enabled the determination of the absolute source coordinates. The combination of the mPSD and the ISD in vivo dosimetry constitutes a promising alternative for real‐time 3D source tracking in HDR brachytherapy. [ABSTRACT FROM AUTHOR]

• Automatic dosimetric verification of online adapted plans on the Unity MR-Linac is feasible using in vivo 3D EPID dosimetry. • Although additional work is required for sites with inhomogeneities, the majority of online adapted plans can be automatically approved without any human intervention. • Discrepancies between the patient model used for online dose calculations and the real anatomy of the patient can be detected. • In vivo EPID dosimetry is ready to replace MR-compatible detector devices for PSQA eliminating thus the time-consuming and laborious tasks of phantom positioning and re-planning. The Unity MR-Linac is equipped with an EPID, the images from which contain information about the dose delivered to the patient. The purpose of this study was to introduce a framework for the automatic dosimetric verification of online adapted plans using 3D EPID dosimetry and to present the obtained dosimetric results. The framework was active during the delivery of 1207 online adapted plans corresponding to 127 clinical IMRT treatments (74 prostate, 19 rectum, 19 liver and 15 lymph node oligometastases). EPID reconstructed dose distributions in the patient geometry were calculated automatically and then compared to the dose distributions calculated online by the treatment planning system (TPS). The comparison was performed by γ-analysis (3% global/2mm/10% threshold) and by the difference in median dose to the high-dose volume (ΔHDV D50). 85% for γ-pass rate and 5% for ΔHDV D50 were used as tolerance limit values. 93% of the online plans were verified automatically by the framework. Missing EPID data was the reason for automation failure. 91% of the verified plans were within tolerance. Automatic dosimetric verification of online adapted plans on the Unity MR-Linac is feasible using in vivo 3D EPID dosimetry. Almost all online adapted plans were approved automatically by the framework. This newly developed framework is a major step forward towards the clinical implementation of a permanent safety net for the entire online adaptive workflow. [ABSTRACT FROM AUTHOR]

Due to the limited height of commercial prone breast boards, large or pendulous breasts may contact the base layer of the board during simulation and throughout the course of treatment. Our clinic has historically identified and marked this region of contact to ensure reproducible setup. However, this situation may result in unwanted hotspots where the breast rests atop the board due to electron scatter. In this study, we performed in‐vivo dosimetric measurements to evaluate the surface dose in regions of contact with the immobilization device. The average dose and hotspot were identified and evaluated to determine whether plan modifications were necessary to avoid excess skin toxicity at the skin/breast board interface. The film method results were validated against a commissioned in vivo OSLD dosimetry system. Radiochromic film measurements agreed with OSLD readings (n = 18) overall within 1%, σ = 6.4%, with one deviation of >10%. Pertinent information for the physician includes the average, maximum, and minimum doses received at the film interface. Future readings will not require OSLD verification. Physicians now have access to additional spatial data to correlate skin toxicity with doses delivered at the skin/breast board interface. This new technique is now an established procedure at our clinic, and can inform future efforts to model enhanced methods to calculate the dosimetric effects from the prone breast board in the treatment planning system. [ABSTRACT FROM AUTHOR]

Purpose: The capability of proton therapy to provide highly conformal dose distributions is impaired by range uncertainties. The aim of this work is to apply range probing (RP), a form of a proton radiography‐based quality control (QC) procedure for range accuracy assessment in head and neck cancer (HNC) patients in a clinical setting. Methods and Materials: This study included seven HNC patients. RP acquisition was performed using a multi‐layer ionization chamber (MLIC). Per patient, two RP frames were acquired within the first two weeks of treatment, on days when a repeated CT scan was obtained. Per RP frame, integral depth dose (IDD) curves of 81 spots around the treatment isocenter were acquired. Range errors are determined as a discrepancy between calculated IDDs in the treatment planning system and measured residual ranges by the MLIC. Range errors are presented relative to the water equivalent path length of individual proton spots. In addition to reporting results for complete measurement frames, an analysis, excluding range error contributions due to anatomical changes, is presented. Results: Discrepancies between measured and calculated ranges are smaller when performing RP calculations on the day‐specific patient anatomy rather than the planning CT. The patient‐specific range evaluation shows an agreement between calculated and measured ranges for spots in anatomically consistent areas within 3% (1.5 standard deviation). Conclusions: The results of an RP‐based QC procedure implemented in the clinical practice for HNC patients have been demonstrated. The agreement of measured and simulated proton ranges confirms the 3% uncertainty margin for robust optimization. Anatomical variations show a predominant effect on range accuracy, motivating efforts towards the implementation of adaptive radiotherapy. [ABSTRACT FROM AUTHOR]

The in vivo dosimetric monitoring in HDR brachytherapy is important for improving patient safety. However, there are very limited options available for clinical application. In this study, we present a new in vivo dose measurement system with a plastic scintillating detector (PSD) for GYN HDR brachytherapy. An FDA approved PSD system, called OARtrac (AngioDynamics, Latham, NY), was used with various applicators for in vivo dose measurements for GYN patients. An institutional workflow was established for the clinical implementation of the dosimetric system. Action levels were proposed based on the measurement and system uncertainty for measurement deviations. From October 2018 to September 2019, a total of 75 measurements (48 fractions) were acquired from 14 patients who underwent HDR brachytherapy using either a multichannel cylinder, Venezia applicator, or Syed-Neblett template. The PSDs were placed in predetermined catheters/channels. A planning CT was acquired for treatment planning in Oncentra (Elekta, Version-4.5.2) TPS. The PSDs were contoured on the CT images, and the PSD D 90% values were used as the expected doses for comparison with the measured doses. The mean difference from patient measurements was −0.22% ± 5.98%, with 26% being the largest deviation from the expected value (Syed case). Large deviations were observed when detectors were placed in the area where dose rates were less than 1 cGy/s. The establishment of clinical workflow for the in vivo dosimetry for both the intracavitary and interstitial GYN HDR brachytherapy will potentially improve the safety of the patient treatment. [ABSTRACT FROM AUTHOR]

Objective. High-dose-rate (HDR) brachytherapy lacks routinely available treatment verification methods. Real-time tracking of the radiation source during HDR brachytherapy can enhance treatment verification capabilities. Recent developments in source tracking allow for measurement of dwell times and source positions with high accuracy. However, more clinically relevant information, such as dose discrepancies, is still needed. To address this, a real-time dose calculation implementation was developed to provide more relevant information from source tracking data. A proof-of-principle of the developed tool was shown using source tracking data obtained from a 3D-printed anthropomorphic phantom. Approach. Software was developed to calculate dose-volume-histograms (DVH) and clinical dose metrics from experimental HDR prostate treatment source tracking data, measured in a realistic pelvic phantom. Uncertainty estimation was performed using repeat measurements to assess the inherent dose measuring uncertainty of the in vivo dosimetry (IVD) system. Using a novel approach, the measurement uncertainty can be incorporated in the dose calculation, and used for evaluation of cumulative dose and clinical dose-volume metrics after every dwell position, enabling real-time treatment verification. Main results. The dose calculated from source tracking measurements aligned with the generated uncertainty bands, validating the approach. Simulated shifts of 3 mm in 5/17 needles in a single plan caused DVH deviations beyond the uncertainty bands, indicating errors occurred during treatment. Clinical dose-volume metrics could be monitored in a time-resolved approach, enabling early detection of treatment plan deviations and prediction of their impact on the final dose that will be delivered in real-time. Significance. Integrating dose calculation with source tracking enhances the clinical relevance of IVD methods. Phantom measurements show that the developed tool aids in tracking treatment progress, detecting errors in real-time and post-treatment evaluation. In addition, it could be used to define patient-specific action limits and error thresholds, while taking the uncertainty of the measurement system into consideration., (Creative Commons Attribution license.)

Background: The increasing use of complex and high dose-rate treatments in radiation therapy necessitates advanced detectors to provide accurate dosimetry. Rather than relying on pre-treatment quality assurance (QA) measurements alone, many countries are now mandating the use of in vivo dosimetry, whereby a dosimeter is placed on the surface of the patient during treatment. Ideally, in vivo detectors should be flexible to conform to a patient's irregular surfaces., Purpose: This study aims to characterize a novel hydrogenated amorphous silicon (a-Si:H) radiation detector for the dosimetry of therapeutic x-ray beams. The detectors are flexible as they are fabricated directly on a flexible polyimide (Kapton) substrate., Methods: The potential of this technology for application as a real-time flexible detector is investigated through a combined dosimetric and flexibility study. Measurements of fundamental dosimetric quantities were obtained including output factor (OF), dose rate dependence (DPP), energy dependence, percentage depth dose (PDD), and angular dependence. The response of the a-Si:H detectors investigated in this study are benchmarked directly against commercially available ionization chambers and solid-state diodes currently employed for QA practices., Results: The a-Si:H detectors exhibit remarkable dose linearities in the direct detection of kV and MV therapeutic x-rays, with calibrated sensitivities ranging from (0.580 ± 0.002) pC/cGy to (19.36 ± 0.10) pC/cGy as a function of detector thickness, area, and applied bias. Regarding dosimetry, the a-Si:H detectors accurately obtained OF measurements that parallel commercially available detector solutions. The PDD response closely matched the expected profile as predicted via Geant4 simulations, a PTW Farmer ionization chamber and a PTW ROOS chamber. The most significant variation in the PDD performance was 5.67%, observed at a depth of 3 mm for detectors operated unbiased. With an external bias, the discrepancy in PDD response from reference data was confined to ± 2.92% for all depths (surface to 250 mm) in water-equivalent plastic. Very little angular dependence is displayed between irradiations at angles of 0° and 180°, with the most significant variation being a 7.71% decrease in collected charge at a 110° relative angle of incidence. Energy dependence and dose per pulse dependence are also reported, with results in agreement with the literature. Most notably, the flexibility of a-Si:H detectors was quantified for sample bending up to a radius of curvature of 7.98 mm, where the recorded photosensitivity degraded by (-4.9 ± 0.6)% of the initial device response when flat. It is essential to mention that this small bending radius is unlikely during in vivo patient dosimetry. In a more realistic scenario, with a bending radius of 15-20 mm, the variation in detector response remained within ± 4%. After substantial bending, the detector's photosensitivity when returned to a flat condition was (99.1 ± 0.5)% of the original response., Conclusions: This work successfully characterizes a flexible detector based on thin-film a-Si:H deposited on a Kapton substrate for applications in therapeutic x-ray dosimetry. The detectors exhibit dosimetric performances that parallel commercially available dosimeters, while also demonstrating excellent flexibility results., (© 2024 The Authors. Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.)

Objective . The primary goal of this research is to demonstrate the feasibility of radiation-induced acoustic imaging (RAI) as a volumetric dosimetry tool for ultra-high dose rate FLASH electron radiotherapy (FLASH-RT) in real time. This technology aims to improve patient outcomes by accurate measurements of in vivo dose delivery to target tumor volumes. Approach . The study utilized the FLASH-capable eRT6 LINAC to deliver electron beams under various doses (1.2 Gy pulse -1 to 4.95 Gy pulse -1 ) and instantaneous dose rates (1.55 × 10 5 Gy s -1 to 2.75 × 10 6 Gy s -1 ), for imaging the beam in water and in a rabbit cadaver with RAI. A custom 256-element matrix ultrasound array was employed for real-time, volumetric (4D) imaging of individual pulses. This allowed for the exploration of dose linearity by varying the dose per pulse and analyzing the results through signal processing and image reconstruction in RAI. Main Results . By varying the dose per pulse through changes in source-to-surface distance, a direct correlation was established between the peak-to-peak amplitudes of pressure waves captured by the RAI system and the radiochromic film dose measurements. This correlation demonstrated dose rate linearity, including in the FLASH regime, without any saturation even at an instantaneous dose rate up to 2.75 × 10 6 Gy s -1 . Further, the use of the 2D matrix array enabled 4D tracking of FLASH electron beam dose distributions on animal tissue for the first time. Significance . This research successfully shows that 4D in vivo dosimetry is feasible during FLASH-RT using a RAI system. It allows for precise spatial (∼mm) and temporal (25 frames s -1 ) monitoring of individual FLASH beamlets during delivery. This advancement is crucial for the clinical translation of FLASH-RT as enhancing the accuracy of dose delivery to the target volume the safety and efficacy of radiotherapeutic procedures will be improved., (© 2024 Institute of Physics and Engineering in Medicine.)

In vivo measurements were made of the dose delivered to animal models in an effort to develop a method for treating cardiac arrhythmia using radiation. This treatment would replace RF energy (currently used to create cardiac scar) with ionizing radiation. In the current study, the pulmonary vein ostia of animal models were irradiated with 6 MV X-rays in order to produce a scar that would block aberrant signals characteristic of atrial fibrillation. The CyberKnife radiosurgery system was used to deliver planned treatments of 20-35 Gy in a single fraction to four animals. The Synchrony system was used to track respiratory motion of the heart, while the contractile motion of the heart was untracked. The dose was measured on the epicardial surface near the right pulmonary vein and on the esophagus using surgically implanted TLD dosimeters, or in the coronary sinus using a MOSFET dosimeter placed using a catheter. The doses measured on the epicardium with TLDs averaged 5% less than predicted for those locations, while doses measured in the coronary sinus with the MOSFET sensor nearest the target averaged 6% less than the predicted dose. The measurements on the esophagus averaged 25% less than predicted. These results provide an indication of the accuracy with which the treatment planning methods accounted for the motion of the target, with its respiratory and cardiac components. This is the first report on the accuracy of CyberKnife dose delivery to cardiac targets.

• Results of in vivo dosimetry for extra-lung SBRT treatments are reported. • Local tolerance levels based on Statistical Process Control theory were established. • In vivo dosimetry was successful to detect errors on extra-lung SBRT treatments. To analyze results from three years of in vivo transit EPID dosimetry of abdominal and pelvic stereotactic radiotherapy and to establish tolerance levels for routine clinical use. 80 stereotactic VMAT treatments (152 fractions) targeting the abdomen or pelvis were analyzed. In vivo 3D doses were reconstructed with an EPID commercial algorithm. Gamma Agreement Index (GAI) and DVH differences in Planning Target Volume (PTV) and Clinical Target Volume (CTV) were evaluated. Initial tolerance level was set to GAI > 85% in PTV. Fractions Over Tolerance Level (OTL) were deemed to be due to set-up errors, incorrect use of immobilization devices, 4D errors, transit EPID algorithm errors and unknown/unidentified errors. Statistical Process Control (SPC) was applied to determine local tolerance levels. Average GAI were (82.7 ± 20.9) % in PTV and (72.9 ± 29.7) % in CTV. 37.8% of fractions resulted OTL and were classified as: set-up errors (3.3%), incorrect use of immobilization devices (2.1%), 4D errors (2.1%), EPID transit algorithm errors (17.1%). OTL causes for the remaining 13.2% of fractions were not identified. The differences between PTV and CTV measured in vivo and calculated mean dose (average difference ± standard deviation) were (−3.3% ± 3.2%) and (−2.3% ± 3.0%). When tolerance levels based on SPC to PTV mean dose differences were applied, the percentage of OTL decreased to 7% and no EPID algorithm error occurred. One error was not identified. The application of local tolerance levels to EPID in vivo dosimetry proved to be useful for detecting extra-lung SBRT treatment errors. [ABSTRACT FROM AUTHOR]

Background: The purpose of this study was to investigate the feasibility of MOSFET dosimeter in measuring eye dose during 2D MV portal imaging for setup verification in radiotherapy. Materials and methods: The in-vivo dose measurements were performed by placing the dosimeters over the eyes of 30 brain patients during the acquisition of portal images in linear accelerator by delivering 1 MU with the field sizes of 10 × 10 cm2 and 15 × 15 cm2. Results: The mean doses received by the left and right eyes of 10 out of 30 patients when both eyes were completely inside the anterior portal field were found to be 2.56 ± 0.2 cGy and 2.75 ± 0.2, respectively. Similarly, for next 10 patients out of the same 30 patients the mean doses to left and right eyes when both eyes were completely out of the anterior portal fields were found to be 0.13 ± 0.02 cGy and 0.17 ± 0.02 cGy, respectively. The mean doses to ipsilateral and contralateral eye for the last 10 patients when one eye was inside the anterior portal field were found to be 3.28 ± 0.2 cGy and 0.36 ± 0.1 cGy, respectively. Conclusion: The promising results obtained during 2D MV portal imaging using MOSFET have shown that this dosimeter is well suitable for assessing low doses during imaging thereby enabling to optimize the imaging procedure using the dosimetric data obtained. In addition, the documentation of the dose received by the patient during imaging procedure is possible with the help of an in-built software in conjunction with the MOSFET reader module. [ABSTRACT FROM AUTHOR]

• Low-energy photon IORT treatments of the breast are increasing in recent years. • The best verification of these treatments is to establish an in vivo dosimetry procedure. • XR-RV3 radiochromic films are a suitable dosimeter for measuring low energy photons at high doses. • An adequate calibration that considers the beam hardening with the distance significantly improves the measurement accuracy. The objectives of the study were to establish a procedure for in vivo film-based dosimetry for intraoperative radiotherapy (IORT), evaluate the typical doses delivered to organs at risk, and verify the dose prescription. In vivo dose measurements were studied using XR-RV3 radiochromic films in 30 patients with breast cancer undergoing IORT using the Axxent® device (Xoft Inc.). The stability of the radiochromic films in the energy ranges used was verified by taking measurements at different depths. The stability of the scanner response was tested, and 5 different calibration curves were constructed for different beam qualities. Six pieces of film were placed in each of the 30 patients. All the pieces were correctly sterilized and checked to ensure that the process did not affect the outcome. All calibration and dose measurements were analyzed using the Radiochromic.com software application. The doses were measured for 30 patients. The doses in contact with the applicator (prescription zone) were 19.8 ± 0.9 Gy. In the skin areas, the doses were as follows: 1–2 cm from the applicator, 1.86 ± 0.77 Gy; 2–5 cm, 0.73 ± 0.14 Gy; and greater than 5 cm, 0.28 ± 0.17 Gy. The dose delivered to the pectoral muscle (tungsten shielding disc) was 0.51 ± 0.27 Gy. The study demonstrated the viability of XR-RV3 films for in vivo dose measurement in the dose and energy ranges applied in a complex procedure, such as breast IORT. The doses in organs at risk were far below the tolerances for cases such as those studied. [ABSTRACT FROM AUTHOR]

• In vivo measurements are useful for quality assurance in rectal cancer IOERT. • Published work mostly focuses on large EBT3 film pieces irradiated one at a time. • This work focuses on digitization of small EBT3 films irradiated simultaneously. • Edge effects and the influence of opaque templates were taken into consideration. • The proposed digitization method is fast and reduces all the relevant uncertainties. Intra-Operative Electron Radiation Therapy (IOERT) is used to treat rectal cancer at our institution, and in vivo measurements with Gafchromic EBT3® films were introduced as quality assurance. The purpose of this work was to quantify the uncertainties associated with digitization of very small EBT3 films irradiated simultaneously, in order to optimize in vivo dosimetry for IOERT. Film samples of different sizes - M1 (5×5cm2), M2 (1.5×1.5 cm2), M3 (1.0×1.5 cm2) and M4 (0.75×1.5 cm2) – were used to quantify typical variations (uncertainties) due to scanner fluctuations, misalignment, film inhomogeneity, long-term effect of film cutting, small rotations, film curling, edge effects and the influence of opaque templates. Fitting functions and temporal validity of sensitometric curves were also assessed. Film curling, intra-film variability and scanner fluctuations are important effects that need to be minimized or considered in the uncertainty budget. Small rotations, misalignments and film cutting have little or no influence on the readings. Most fitting functions perform well, but the quantity used for dose quantification determines over- or under-valuation of dose in the long term. Edge effects and the influence of opaque templates need to be well understood, to allow optimization of methodology to the intended purpose. The proposed method allows practical and simultaneous digitization of up to ten small irradiated film samples, with an experimental uncertainty of 1%. [ABSTRACT FROM AUTHOR]

Background/Aim: In this study, a new method to create a customized three-dimensional (3D) bolus by accurately considering the anatomy of an individual patient is demonstrated. Patients and Methods: A 3D bolus structure was created from an extended planning target volume (PTV) to reduce an inevitable skin reaction. In addition, during computed tomography simulation in patients with oral cavity cancers, a balloon was inserted into the mouth of a patient to secure space, and then the area surrounding the balloon was designed into a 3D bolus structure. Results: For patients with head and neck cancers, a customized 3D bolus can reduce the unnecessary skin dose by 14.4% compared to a commercial bolus. For patients with oral cavity cancer, the PTV and tongue doses were 93.8% and 8% of the prescribed dose, respectively. Conclusion: The customized 3D bolus enables effective skin sparing and full coverage of the target area. [ABSTRACT FROM AUTHOR]

Topometry is an integral part of irradiation whose task is to repeat the position of the patient set by the simulator to repeat the PTV and the spatial relationship between the radiation field and the risk organs that were identified during planning. The dose distribution formulated in the plan is only an ideal model. There is some gap between the actual and planned dose distribution, especially in overweight patients. Objective: evaluate the effect of anthropometric data on the deviation between the planned dose and the results of dosimetry in vivo in patients with uterine cancer during postoperative irradiation. Materials and Methods. The authors analyzed the results of treatment of 110 patients with stage IB–II uterine cancer who were treated at the Department of Radiation Therapy of the Institute of Medical Radiology and Oncology of the National Academy of Medical Sciences of Ukraine from 2016 to 2019. The technique of classical fractionation was used with a single focal dose of 2.0 Gy 5 times a week, the total focal dose was 42.0–50.0 Gy. To assess the effect of the patient’s anthropometric data on the difference between the actual and calculated dose, the authors per& formed in vivo dosimetry after the first session and in the middle of the postoperative course of external beam radiation therapy. Results. Рatients with BSA < 1.92 m², had the median relative deviation at the first session -4.12 %, after 20.0 Gy – 3.61 %, patients with BSA > 1.92 m²: -2.06 % and -1.55 % respectively. After 20 Gy 34.8 % of patients with BSA < 1.92 m² there was an increase in deviation from the planned dose, 65.2 % a decrease, while in 56.1 % of patients with BSA > 1.92 m² there was an increase, and in 43.9 % – its reduction. With increasing BMI, the actual dose received on the rectal mucosa in the tenth session of irradiation is approaching the calculated one. Conclusions. When irradiated on the ROKUS-AM device, we did not find a probable dependence of the influence of the constitutional features of patients between the received and planned radiation dose. When treated with a Clinac 600 C, only body weight and body mass index at the tenth irradiation session have a likely effect on the dose difference. Therefore, issues related to the individual approach to the treatment of uterine cancer, depending on anthropometric data is an urgent problem of modern radiotherapy. Topometry is an integral part of irradiation whose task is to repeat the position of the patient set by the simulator to repeat the PTV and the spatial relationship between the radiation field and the risk organs that were identified during planning. The dose distribution formulated in the plan is only an ideal model. There is some gap between the actual and planned dose distribution, especially in overweight patients. Objective: evaluate the effect of anthropometric data on the deviation between the planned dose and the results of dosimetry in vivo in patients with uterine cancer during postoperative irradiation. Materials and Methods. The authors analyzed the results of treatment of 110 patients with stage IB–II uterine cancer who were treated at the Department of Radiation Therapy of the Institute of Medical Radiology and Oncology of the National Academy of Medical Sciences of Ukraine from 2016 to 2019. The technique of classical fractionation was used with a single focal dose of 2.0 Gy 5 times a week, the total focal dose was 42.0–50.0 Gy. To assess the effect of the patient’s anthropometric data on the difference between the actual and calculated dose, the authors per& formed in vivo dosimetry after the first session and in the middle of the postoperative course of external beam radiation therapy. Results. Рatients with BSA < 1.92 m², had the median relative deviation at the first session -4.12 %, after 20.0 Gy – 3.61 %, patients with BSA > 1.92 m²: -2.06 % and -1.55 % respectively. After 20 Gy 34.8 % of patients with BSA < 1.92 m² there was an increase in deviation from the planned dose, 65.2 % a decrease, while in 56.1 % of patients with BSA > 1.92 m² there was an increase, and in 43.9 % – its reduction. With increasing BMI, the actual dose received on the rectal mucosa in the tenth session of irradiation is approaching the calculated one. Conclusions. When irradiated on the ROKUS-AM device, we did not find a probable dependence of the influence of the constitutional features of patients between the received and planned radiation dose. When treated with a Clinac 600 C, only body weight and body mass index at the tenth irradiation session have a likely effect on the dose difference. Therefore, issues related to the individual approach to the treatment of uterine cancer, depending on anthropometric data is an urgent problem of modern radiotherapy. [ABSTRACT FROM AUTHOR]

• Deep learning is a promising powerful tool for identifying treatment errors with EPID dosimetry. • Simulated treatment errors can be detected to a high level of detail, including error type and magnitude. • Detailed error classification provides additional information not currently available from EPID dosimetry. Electronic portal imaging device (EPID) dosimetry aims to detect treatment errors, potentially leading to treatment adaptation. Clinically used threshold classification methods for detecting errors lead to loss of information (from multi-dimensional EPID data to a few numbers) and cannot be used for identifying causes of errors. Advanced classification methods, such as deep learning, can use all available information. In this study, convolutional neural networks (CNNs) were trained to detect and identify error type and magnitude of simulated treatment errors in lung cancer patients. The purpose of this simulation study is to provide a proof-of-concept of CNNs for error identification using EPID dosimetry in an in vivo scenario. Clinically realistic ranges of anatomical changes, positioning errors and mechanical errors were simulated for lung cancer patients. Predicted portal dose images (PDIs) containing errors were compared to error-free PDIs using the widely used gamma analysis. CNNs were trained to classify errors using 2D gamma maps. Three classification levels were assessed: Level 1 (main error type, e.g., anatomical change), Level 2 (error subtype, e.g., tumor regression) and Level 3 (error magnitude, e.g., >50% tumor regression). CNNs showed good performance for all classification levels (training/test accuracy 99.5%/96.1%, 92.5%/86.8%, 82.0%/72.9%). For Level 3, overfitting became more apparent. This simulation study indicates that deep learning is a promising powerful tool for identifying types and magnitude of treatment errors with EPID dosimetry, providing additional information not currently available from EPID dosimetry. This is a first step towards rapid, automated models for identification of treatment errors using EPID dosimetry. [ABSTRACT FROM AUTHOR]

We evaluate the combined usage of two systems, the Integral Quality Monitor (IQM) transmission detector and SoftDiso software, for in vivo dose monitoring by simultaneous detection of delivery and patient setup errors in whole breast irradiation. An Alderson RANDO phantom was adapted with silicon breast prostheses to mimic the female anatomy. Plans with simulated delivery errors were created from a reference left breast plan, and patient setup errors were simulated by moving the phantom. Deviations from reference values recorded by both monitoring systems were measured for all plans and phantom positions. A 2D global gamma analysis was performed in SoftDiso for all phantom displacements. Both IQM signals and SoftDiso R-values are sensitive to small MU variations. However, only IQM is sensitive to jaw position variations. Conversely, IQM is unable to detect patient positioning errors, and the R-value has good sensitivity to phantom displacements. A gamma comparison analysis allows one to determine alert thresholds to detect phantom shifts or relatively large rotations. The combined use of the IQM and SoftDiso allows for fast identification of both delivery and setup errors and substantially reduces the impact of error identification and correction on the treatment workflow. [ABSTRACT FROM AUTHOR]

Purpose: To develop an in vivo dosimeter system for stereotactic body radiation therapy (SBRT) that can perform accurate and precise real‐time measurements, using a microsized amount of a photostimulable phosphor (PSP), BaFBr:Eu2+. Methods: The sensitive volume of the PSP was 1.26 × 10−5 cm3. The dosimeter system was designed to apply photostimulation to the PSP after the decay of noise signals, in synchronization with the photon beam pulse of a linear accelerator (LINAC), to eliminate the noise signals completely using a time separation technique. The noise signals included stem signals, and radioluminescence signals generated by the PSP. In addition, the dosimeter system was built on a storage‐type dosimeter that could read out a signal after an arbitrary preset number of photon beam pulses were incident. First, the noise and photostimulated luminescence (PSL) signal decay times were measured. Subsequently, we confirmed that the PSL signals could be exclusively read out within the photon beam pulse interval. Finally, using a water phantom, the basic characteristics of the dosimeter system were demonstrated under SBRT conditions, and the feasibility for clinical application was investigated. The reproducibility, dose linearity, dose‐rate dependence, temperature dependence, and angular dependence were evaluated. The feasibility was confirmed by measurements at various dose gradients and using a representative treatment plan for a metastatic liver tumor. A clinical plan was created with a two‐arc beam volumetric modulated arc therapy using a 10 MV flattening filter‐free photon beam. For the water phantom measurements, the clinical plan was compiled into a plan with a fixed gantry angle of 0°. To evaluate the energy dependence during SBRT, the percent depth dose (PDD) was measured and compared with those calculated via Monte Carlo (MC) simulations. Results: All the PSL signals could be read out while eliminating the noise signals within the minimum pulse interval of the LINAC. Stable real‐time measurements could be performed with a time resolution of 56 ms (i.e., number of pulses = 20). The dose linearity was good in the dose range of 0.01–100 Gy. The measurements agreed within 1% at dose rates of 40–2400 cGy/min. The temperature and angular dependence were also acceptable since these dependencies had only a negligible effect on the measurements in SBRT. At a dose gradient of 2.21 Gy/mm, the measured dose agreed with that calculated using a treatment planning system (TPS) within the measurement uncertainties due to the probe position. For measurements using a representative treatment plan, the measured dose agreed with that calculated using the TPS within 0.5% at the center of the beam axis. The PDD measurements agreed with the MC calculations to within 1% for field sizes <5 × 5 cm2. Conclusion: The in vivo dosimeter system developed using BaFBr:Eu2+ is capable of real‐time, accurate, and precise measurement under SBRT conditions. The probe is smaller than a conventional dosimeter, has excellent spatial resolution, and can be valuable in SBRT with a steep dose distribution over a small field. The developed PSP dosimeter system appears to be suitable for in vivo SBRT dosimetry. [ABSTRACT FROM AUTHOR]

Purpose: FLASH radiotherapy (FLASH‐RT) is a novel irradiation modality with ultra‐high dose rates (>40 Gy/s) that have shown tremendous promise for its ability to enhance normal tissue sparing while maintaining comparable tumor cell eradication toconventional radiotherapy (CONV‐RT). Due to its extremely high dose rates, clinical translation of FLASH‐RT is hampered by risky delivery and current limitations in dosimetric devices, which cannot accurately measure, in real time, dose at deeper tissue. This work aims to investigate ionizing radiation acoustic imaging (iRAI) as a promising image‐guidance modality for real‐time deep tissue dose measurements during FLASH‐RT. The underlying hypothesis is that iRAI can enable mapping of dose deposition with respect to surrounding tissue with a single linear accelerator (linac) pulse precision in real time. In this work, the relationship between iRAI signal response and deposited dose was investigated as well as the feasibility of using a proof‐of‐concept dual‐modality imaging system of ultrasound and iRAI for treatment beam co‐localization with respect to underlying anatomy. Methods: Two experimental setups were used to study the feasibility of iRAI for FLASH‐RT using 6 MeV electrons from a modified Varian Clinac. First, experiments were conducted using a single element focused transducer to take a series of point measurements in a gelatin phantom, which was compared with independent dose measurements using GAFchromic film. Secondly, an ultrasound and iRAI dual‐modality imaging system utilizing a phased array transducer was used to take coregistered two‐dimensional (2D) iRAI signal amplitude images as well as ultrasound B‐mode images, to map the dose deposition with respect to surrounding anatomy in an ex vivo rabbit liver model with a single linac pulse precision. Results: Using a single element transducer, iRAI measurements showed a highly linear relationship between the iRAI signal amplitude and the linac dose per pulse (r2 = 0.9998) with a repeatability precision of 1% and a dose resolution error <2.5% in a homogenous phantom when compared to GAFchromic film dose measurements. These phantom results were used to develop a calibration curve between the iRAI signal response and the delivered dose per pulse. Subsequently, a normalized depth dose curve was generated that agreed with film measurements with an RMSE of 0.0243, using correction factors to account for deviations in measurement conditions with respect to calibration. Experiments on the ex‐vivo rabbit liver model demonstrated that a 2D iRAI image could be generated successfully from a single linac pulse, which was fused with the B‐mode ultrasound image to provide information about the beam position with respect to surrounding anatomy in real time. Conclusion: This work demonstrates the potential of using iRAI for real‐time deep tissue dosimetry in FLASH‐RT. Our results show that iRAI signals are linear with dose and can accurately map the delivered radiation dose with respect to soft tissue anatomy. With its ability to measure dose for individual linac pulses at any location within surrounding soft tissue while identifying where that dose is being delivered anatomically in real time, iRAI can be an indispensable tool to enable safe and efficient clinical translation of FLASH‐RT. [ABSTRACT FROM AUTHOR]

The performing of IVD for Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) is not well established and the studies and trails available are not sufficient to give us a clear view of the verified IVD methods in modulated radiotherapy. The objective of this study was to give validation of using diodes and TLDs for in vivo dosimetry in advanced radiotherapy techniques for early detection the uncertainties and significant errors of the dose delivery. Thirty nine patients (23 female and 16 male) with different clinical sites were selected for this study. The period of the study last for five months at Children's Cancer Hospital 57357 and we used paediatric anthropomorphic A 10-years-old phantom to measure doses in IMRT and VMAT by using Thermoluminescent Dosimeters (TLDs) and semiconductor diodes. Also, we utilized the Treatment Planning System (TPS) to calculate doses and compared it with detector readings. Diode is good to be used in IMRT but avoiding total blocked and partial blocked region of MLC that effective on measured diode ± 6 %. Diode is not valid to be used in VMAT cased orientate and dynamic MLC. Result of measurement with TLD in IMRT is less in accuracy than that for VMAT distribution at the edges. The penumbra edges have a percentage difference of ±10 % while it is very close to zero at the middle region. We have evaluated the use of diodes and TLD for application to IMRT and VMAT in vivo dosimetry. Phantom measurements in which diode and TLD used were compared, showing them to be in agreement to generally better than 90%. In comparison with plan prediction of TPS doses, average percent differences in the phantom measurements and patients also were mostly within 35%, with some discrepancies. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to present the performance of a multipoint plastic scintillation detector (mPSD) as a tool for real‐time dose measurements (covering three orders of magnitude in dose rate), source‐position triangulation, and dwell time assessment in high dose rate (HDR) brachytherapy. Methods: A previously characterized and optimized three‐point sensor system was used for HDR brachytherapy measurements. The detector was composed of three scintillators: BCF60, BCF12, and BCF10. Scintillation light was transmitted through a single 1‐mm‐diameter clear optical fiber and read by a compact assembly of photomultiplier tubes (PMTs). Each component was numerically optimized to allow for signal deconvolution using a multispectral approach, taking care of the Cerenkov stem effect as well as extracting the dose from each scintillator. The PMTs were read simultaneously using a data acquisition board at a rate of 100 KHz and controlled with in‐house software based on Python. An 192Ir source (Flexitron, Elekta‐Brachy) was remotely controlled and sent to various positions in a in‐house PMMA holder, ensuring 0.1 mm positional accuracy. Dose measurements covering a range of 10 cm of source movement were carried out according to TG‐43 U1 recommendations. Water measurements were performed in order to: (a) characterize the system's response in terms of angular dependence; (b) obtain the relative contribution of positioning and measurement uncertainties to the total system uncertainty; (c) assess the system's temporal resolution; and (d) track the source position in real time. The triangulation principle was applied to report the source position in three‐dimensional space. Results: As expected, the positioning uncertainty dominated close to the source, whereas the measurement uncertainty dominated at larger distances. A maximum measurement uncertainty of 17 % was observed for the BCF60 scintillator at 10 cm from the source. Based on the uncertainty chain, the best compromises between positioning and measurement uncertainties were reached at 17.2, 17.4, and 17.5 mm for the BCF10, BCF12, and BCF60 scintillators, respectively, which also corresponded to the recommended optimal distances to the source for calibration purposes. The detector further exhibited no angular dependence. All dose values were found to be within 2% of the dose value at 90∘. In the experiments performed for source‐position determination, the system provided an average location with a standard deviation under 1.7 mm. The maximum observed differences between measured and expected values were 1.82 and 1.8 mm in the x‐ and z‐directions, respectively. Deviations between the mPSD measurements and expected TG‐43 values were below 5% in all the explored measurement conditions. With regard to dwell time measurement accuracy, the maximum deviation observed at all distances was 0.56 ± 0.25 s, with a weighted average of the three scintillators below 0.33 ± 0.37 s at all distances covered in this study. Conclusions: Real‐time HDR brachytherapy measurements were performed with an optimized mPSD system. The performance of the system demonstrated that it could be used for simultaneous, in vivo, real‐time reporting of dose, dwell time, and source position during HDR brachytherapy. [ABSTRACT FROM AUTHOR]

• Error detection thresholds in prostate brachytherapy in vivo dosimetry were evaluated. • Measurements showed good agreement with planned dose within the uncertainties. • A 2–3 mm distance tolerance balances error detection against treatment interruptions. Routine real time in vivo dosimetry (IVD) is performed in HDR prostate brachytherapy to independently verify dose delivery. This study investigates impact of position uncertainty on error detection thresholds for IVD. IVD is implemented using a microMOSFET placed centrally in the prostate using an additional needle. 144 IVD measurements were made for 15 Gy or 19 Gy single fraction treatments. Needle insertion and treatment planning used real-time trans-rectal ultrasound. Source-MOSFET position thresholds of ±1, ±2 and ±3 mm were used to calculate per-needle and total plan error detection thresholds for the measured dose using an uncertainty analysis based on the treatment plan data. The median dose difference from 144 total plan measurements was –5.2% (range +7.4% to –17.3%). 3 plans measured outside the total plan error detection threshold for position threshold ±1 mm, no plans measured outside the total plan error detection threshold for larger position thresholds. For 2233 individual needle measurements, for position thresholds of ±1 mm, ±2mm and ±3 mm the number of needles outside the per-needle error detection threshold was 103, 25 and 10 respectively and the number of treatments that would have required interruption based on these thresholds for real-time IVD was 66, 16 and 8 respectively. IVD in HDR prostate brachytherapy using a microMOSFET provides a high level of confidence that we are correctly delivering the planned dose to our patients. A ±2–3 mm position threshold gives an appropriate balance between error detection and avoiding unnecessary treatment interruptions. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the dose response of optically stimulated luminescent dosimeters (OSLDs), and how this response changes with repeated use, increased accumulated dose, and bleaching light with or without a UV component. To devise a method to stabilize dose response characteristics of OSLDs that are used repeatedly. To decrease measurement uncertainty. Methods: Optically stimulated luminescent dosimeters irradiations were made using a linear accelerator and Ir‐192. The OSLDs (InLight nanoDots) dose response was characterized for these various irradiations under the batch, single use, method and the repeated irradiation method. Some nanoDots were preirradiated with hundreds of Gray of dose with Ir‐192 gamma rays. Repeated use OSLDs were bleached with lights that had different UV content. A special bleaching light was fabricated and used that had the same spectrum as the light in the OSLD reader. Results: New, never irradiated, nanoDots had their characteristics altered by illumination with bleaching light that had a UV component. Each new nanoDot had unique sensitivity to dose as well as a unique linearity factor, which was supra‐linear. NanoDots that were irradiated and bleached repeatedly had changes in low and high dose sensitivity that was altered if the bleaching light had UV in its spectrum. For nanoDots that have been preirradiated with up to 1500 Gy of dose, their dose response was supra‐linear for bleaching light without UV content and infra‐linear for light with UV content. Preirradiated nanoDots that were bleached with light without UV content had stable dose sensitivity (±1.5%), stable linearity factor (±3.5%) for over 10 bleaching cycles, nonlinear response that was quadratic in dose, and dose measurement uncertainty of ±1.4% for 277 measurements. Conclusions: The UV component in bleaching light has an impact on the dose sensitivity characteristics shown by new or repeatedly irradiated nanoDots. Each new nanoDot has a unique sensitivity to dose as well as a unique linearity factor, which was supra‐linear. As nanoDots accumulate dose with repeated use they change sensitivity to low and high dose very differently based on the UV content of the bleaching light. For nanoDots that have been preirradiated with hundreds of Gray of dose their dose response was supra‐linear for bleaching light without UV content and infra‐linear for light that has UV content. NanoDots can be used repeatedly and have stable dose response characteristics if they are preirradiated and bleached with light without UV content. Dose can be measured with an uncertainty of 1.4%, which is a threefold reduction of the uncertainty found with the single use batch method recommended by the manufacturer. [ABSTRACT FROM AUTHOR]