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Treatment planning in high dose‐rate brachytherapy has traditionally been conducted with manual forward planning, but inverse planning is today increasingly used in clinical practice. There is a large variety of proposed optimization models and algorithms to model and solve the treatment planning problem. Two major parts of inverse treatment planning for which mathematical optimization can be used are the decisions about catheter placement and dwell time distributions. Both these problems as well as integrated approaches are included in this review. The proposed models include linear penalty models, dose–volume models, mean‐tail dose models, quadratic penalty models, radiobiological models, and multiobjective models. The aim of this survey is twofold: (i) to give a broad overview over mathematical optimization models used for treatment planning of brachytherapy and (ii) to provide mathematical analyses and comparisons between models. New technologies for brachytherapy treatments and methods for treatment planning are also discussed. Of particular interest for future research is a thorough comparison between optimization models and algorithms on the same dataset, and clinical validation of proposed optimization approaches with respect to patient outcome. Funding: Swedish Research CouncilSwedish Research CouncilEuropean Commission [VR-NT 2015-04543]; Swedish Cancer SocietySwedish Cancer Society [CAN 2017/1029, CAN 2018/622]

PURPOSE Application of linear-quadratic (LQ) model to large fractional dose treatments is inconsistent with observed cell survival curves having a straight portion at high doses. We have proposed a unified multi-activation (UMA) model to fit cell survival curves over the entire dose range that allows us to calculate EQD2 for hypofractionated SBRT, SRT, SRS, and HDRB. METHODS A unified formula of cell survival S=n/eDDo+n-1 using only the extrapolation number of n and the dose slope of Do was derived. Coefficient of determination, R2 , relative residuals, r, and relative experimental errors, e, normalized to survival fraction at each dose point, were calculated to quantify the goodness in modeling of a survival curve. Analytical solutions for α and β, the coefficients respectively describe the linear and quadratic parts of the survival curve, as well as the α/β ratio for the LQ model and EQD2 at any fractional doses were derived for tumor cells undertaking any fractionated radiation therapy. RESULTS Our proposed model fits survival curves of in-vivo and in-vitro tumor cells with R2 > 0.97 and r

Purpose We developed a novel and simple method to measure the source positions in applicators directly for high-dose-rate (HDR) brachytherapy based on Cherenkov emission imaging, and evaluated the performance. Methods The light emission from plastic applicators used in cervical cancer treatments, irradiated by an 192 Ir γ-ray source, was captured using a charge-coupled device camera. Moreover, we attached plastics of different shapes, including tapes, tubes, and plates to a metal applicator, to use as screens for the Cherenkov imaging. We determined the source positions and dwell intervals from the light profiles along with the applicator and compared these with preset values and dummy marker measurements. Results The source positions and dwell intervals measured from the light images were comparable to the dummy marker measurements and preset values. The distance from the applicator tip to the first source positions agreed with the dummy marker measurements within 0.2 mm for the plastic tandem. The dwell intervals measured using the Cherenkov method agreed with the preset values within 0.6 mm. The distances measured with three plastic types on the metal applicator also agreed with the dummy marker measurements within 0.2 mm. The dwell intervals measured using the plastic tape agreed with the preset values within 0.7 mm. Conclusions The proposed method should be suitable for rapid and easy quality assurance (QA) investigations in HDR brachytherapy, as it enables source position using a single image. The method allows for real-time, filmless measurements of the source positions to be obtained and is useful for rapid feedback in QA procedures.

PURPOSE The objective of this study was to characterize the Best Medical Canada microMOSFET detectors for their application in in vivo dosimetry for high-dose-rate brachytherapy (HDRBT) with 192 Ir. We also developed a mathematical model to correct dependencies under the measurement conditions of these detectors. METHODS We analyzed the linearity, reproducibility, and interdetector variability and studied the microMOSFET response dependence on temperature, source-detector distance, and angular orientation of the receptor with respect to the source. The correction model was applied to 19 measurements corresponding to five simulated treatments in a custom phantom specifically designed for this purpose. RESULTS The detectors (high bias applied in all measurements) showed excellent linearity up to 160 Gy. The response dependence on source-detector distance varied by (8.65 ± 0.06)% (k = 1) for distances between 1 and 7 cm, and the variation with temperature was (2.24 ± 0.05)% (k = 1) between 294 and 310 K. The response difference due to angular dependence can reach (10.3 ± 1.3)% (k = 1). For the set of measurements analyzed, regarding angular dependences, the mean difference between administered and measured doses was -4.17% (standard deviation of 3.4%); after application of the proposed correction model, the mean difference was -0.1% (standard deviation of 2.2%). For the treatments analyzed, the average difference between calculations and measures was 4.7% when only the calibration coefficient was used, but it is reduced to 0.9% when the correction model is applied. CONCLUSION Important response dependencies of microMOSFET detectors used for in vivo dosimetry in HDRBT treatments, especially the angular dependence, can be adequately characterized by a correction model that increases the accuracy of this system in clinical applications.

Purpose To evaluate the electromagnetic (EM) tracking of endoscopes and applicators as a method of positioning a high dose rate (HDR) luminal applicator. Method An anatomical phantom consisting of a rigid trachea and flexible esophagus was used to compare applicator placement measurements using EM tracking vs the traditional method using two-dimensional (2D) fluoroscopy and surface skin markers. The phantom included a tumor in the esophagus and several pairs of optically visible points inside the lumen that were used to simulate proximal and distal ends of tumors of varying lengths. The esophagus tumor and lung points were visible on a computed tomography (CT) image of the phantom, which was used as ground truth for the measurements. The EM tracking system was registered to the CT image using fiducial markers. A flexible endoscope was tracked using the EM system and the locations of the proximal and distal ends of the tumor identified and this position recorded. An EM-tracked applicator was then inserted and positioned relative to the tumor markings. The applicator path was mapped using the EM tracking. The gross tumor length (GTL) and the distance between the first dwell position and distal edge of tumor (offset) were measured using the EM tracking and 2D fluoroscopy methods and compared to the same measurements on the CT image. Results The errors in GTL using EM tracking were on average -0.5 ± 1.7 mm and 0.7 ± 3.6 mm for esophagus and lung measurements, similar to errors measured using the 2D fluoroscopy method of -0.9 ± 1.2 mm and 3.4 ± 4.4 mm. Offset measurements were slightly larger while using EM tracking relative to the fluoroscopy method but these were not statistically significant. Conclusions Electromagnetic tracking for placement of lumen applicators is feasible and accurate. Tracking of the endoscope that is used to identify the proximal and distal ends of the tumor and of the applicator during insertion generates accurate three-dimensional measurements of the applicator path, GTL and offset. Guiding the placement of intraluminal applicators using EM navigation is potentially attractive for cases with complex insertions, such as those with nonlinear paths or multiple applicator insertions.

Purpose Intensity modulated brachytherapy (IMBT) is a novel high dose rate brachytherapy (HDR BT) technique which incorporates static or dynamic shielding to increase tumor coverage and/or spare healthy tissues. The purpose of this study is to present a novel delivery system (AIM-Brachy) design that can enable dynamic-shield IMBT for prostate cancer. Methods The AIM-Brachy system dynamically controls the rotation of platinum shields, placed within interstitial catheters, which partially collimate the radiation emitted from an 169 Yb source. Conventional HDR BT (10 Ci 192 Ir) and IMBT (18 Ci 169 Yb) plans were generated for 12 patients using an in-house column generation-based optimizer, coupled to a Geant4-based dose calculation engine, RapidBrachyMC. Treatment plans were normalized to match the same PTV D90 coverage as the clinical plan. Intershield attenuation effects were taken into account. A sensitivity analysis was performed to evaluate the dosimetric impact of systematic longitudinal source positioning errors ( ± 1 mm, ± 2 mm, and ± 3 mm) and rotational errors ( ± 5 ∘ , ± 10 ∘ , and ± 15 ∘ ) on clinically relevant parameters (PTV D90 and urethra D10 ). Results The platinum shield reduced the dose rate on the shielded side at 1 cm to 18.1% of the dose rate on the unshielded side. For equal PTV D90 coverage, the urethral D10 was reduced by 13.3% ± 4.7%, without change to other plan quality indices (PTV V100 , V150, V200 , bladder V75 , rectum V75 , HI, COIN). Delivery times for HDR BT and IMBT were 9.2 ± 1.6 min and 18.6 ± 4.0 min, respectively. In general, the PTV D90 was more sensitive to source positioning errors than rotational errors, while the urethral D10 was more sensitive to rotational errors than source positioning errors. For a typical range of positioning errors ( ± 1 mm, ± 5 ∘ ), the overall tolerance was Conclusions The AIM-Brachy system was proposed to deliver dynamic-shield IMBT for prostate cancer with the potential to create a low dose tunnel within the urethra. The urethra-sparing properties are desirable to minimize the occurrence and severity of urethral strictures or, alternatively, to provide a method for dose escalation.

Purpose: The purpose of this study is to improve upon a recently introduced bi-objective treatment planning method for prostate high-dose-rate (HDR) brachytherapy (BT), both in terms of resulting plan quality and runtime requirements, to the extent that its execution time is clinically acceptable. Methods: Bi-objective treatment planning is done using a state-of-the-art multiobjective evolutionary algorithm, which produces a large number of potential treatment plans with different trade-offs between coverage of the target volumes and sparing organs at risk. A graphics processing unit (GPU) is used for large-scale parallelization of dose calculations and the calculation of the dose-volume (DV) indices of potential treatment plans. Moreover, the objectives of the previously used bi-objective optimization model are modified to produce better results. Results: We applied the GPU-accelerated bi-objective treatment planning method to a set of 18 patients, resulting in a set containing a few hundred potential treatment plans with different trade-offs for each of these patients. Due to accelerations introduced in this article, results previously achieved after 1 hour are now achieved within 30 seconds of optimization. We found plans satisfying the clinical protocol for 15 of 18 patients, whereas this was the case for only 4 of 18 clinical plans. Higher quality treatment plans are obtained when the accuracy of DV index calculation is increased using more dose calculation points, requiring still no more than 3 minutes of optimization for 100 000 points. Conclusions: Large sets of high-quality treatment plans that trade-off coverage and sparing are now achievable within 30 seconds, due to the GPU-acceleration of a previously introduced bi-objective treatment planning method for prostate HDR brachytherapy. Higher quality plans can be achieved when optimizing for 3 minutes, which we still consider to be clinically acceptable. This allows for more insightful treatment plan selection in a clinical setting.

Purpose The purpose of this study is to investigate the role of the centroidal Voronoi tessellation (CVT) and constrained CVT (CCVT) in inverse planning in combination with the Hybrid Inverse Planning Optimization (HIPO) algorithm in HDR brachytherapy of prostate cancer. HIPO implemented in Oncentra© Prostate treatment planning system, is used for three-dimensional (3D)-ultrasound-based intraoperative treatment planning in high dose rate brachytherapy. HIPO utilizes a hybrid iterative process to determine the most appropriate placement of a given number of catheters to fulfil predefined dose-volume constraints. The main goals of the current investigation were to identify a way of improving the performance of HIPO inverse planning; accelerating the HIPO, and to evaluate the effect of the two CVT-based initialization methods on the dose distribution in the sub-region of prostate that is not accessible by catheters, when trying to avoid perforation of urethra. Methods We implemented the CVT algorithm to generate initial catheter configurations before the initialization of the HIPO algorithm. We introduced the CCVT algorithm to improve the dose distribution to the sub-volume of prostate within the bounding box of the urethra contours including its upper vertical extension (U-P). For the evaluation, we considered a total of 15 3D ultrasound-based HDRBT prostate implants. Execution time and treatment plan quality were evaluated based on the dose-volume histograms of prostate (PTV), its sub-volume U-P, and organs at risk (OARs). Furthermore, the conformity index COIN, the homogeneity index HI and the complication-free tumor control probability (P+ ) were used for our treatment plan comparisons. Finally, the plans with the recommended HIPO execution mode were compared to the clinically used intraoperative pre-plans. Results The plan quality achieved with CCVT-based HIPO initialization was superior to the default HIPO initialization method. Focusing on the U-P sub-region of the prostate, the CCVT method resulted in a significant improvement of all dosimetric indices compared to the default HIPO, when both were executed in the adaptive mode. For that recommended HIPO execution mode, and for U-P, CCVT demonstrated in general higher dosimetric indices than CVT. Additionally, the execution time of CCVT initialized HIPO was lower compared to both alternative initialization methods. This is also valid for the values of the aggregate objective function with the differences to the default initialization method being highly significant. Paired non-parametric statistical tests (Wilcoxon signed-rank) showed a significant improvement of dose-volume indices, COIN and P+ for the plans generated by the CCVT-based catheter configuration initialization in HIPO compared to the default HIPO initialization process. Furthermore, in ten out of 15 cases, the CCVT-based HIPO plans fulfilled all the clinical dose-volume constraints in a single trial without any need for further catheter position adaption. Conclusion HIPO with CCVT-based initialization demonstrates better performance regarding the aggregate objective function and convergence when compared to the CVT-based and default catheter configuration initialization methods. This improved performance of HIPO inverse planning is clearly not at the cost of the dosimetric and radiobiologically evaluated plan quality. We recommend the use of the CCVT method for HIPO initialization especially in the adaptive planning mode.

Purpose To present and quantify the effectiveness of a method for the efficient production of 169 Yb high-dose-rate brachytherapy sources with 27 Ci activity upon clinical delivery, which have about the same dose rate in water at 1 cm from the source center as 10 Ci 192 Ir sources. Materials A theoretical framework for 169 Yb source activation and reactivation using thermal neutrons in a research reactor and 168 Yb-Yb2 O3 precursor is derived and benchmarked against published data. The model is dependent primarily on precursor 168 Yb enrichment percentage, active source volume of the active element, and average thermal neutron flux within the active source. Results Efficiency gains in 169 Yb source production are achievable through reactivation, and the gains increase with active source volume. For an average thermal neutron flux within the active source of 1 × 1014 n cm-2 s-1 , increasing the active source volume from 1 to 3 mm3 decreased reactor-days needed to generate one clinic-year of 169 Yb from 256 days yr-1 to 59 days yr-1 , and 82%-enriched precursor dropped from 80 mg yr-1 to 21 mg yr-1 . A resource reduction of 74%-77% is predicted for an active source volume increase from 1 to 3 mm3 . Conclusions Dramatic cost savings are achievable in 169 Yb source production costs through reactivation if active sources larger than 1 mm3 are used.

Purpose Brachytherapy is a treatment modality which delivers large doses of radiation in a reduced number of visits. Since a small number of large dose-per-fraction is administered in high dose rate brachytherapy, ensuring the right dose is delivered is highly critical. In this work, a scintillation detector is coupled to an electromagnetic (EM) sensor (NDI, Waterloo, ON, Canada) having submillimeter positional accuracy for real-time tracking of the dosimeter position. However, adding an EM sensor adds materials in the path to the scintillator and thus could potentially perturb the dose measurements. This study assesses four different sensors for a plastic scintillation detector-EM sensor coupled dosimeter. Methods To confirm the perturbation presence, different sensors were placed in front of the scintillator so the radiation does not arrive to it directly. Variation of the distance between the sensor and the scintillator was used to quantify the effect on the signal at 0 ∘ and 90 ∘ . To test the signal's angular dependence for each sensor, the signal measurement was taken from 0 ∘ to 90 ∘ with 10 ∘ increment. Results The Aurora 5DOF-610090 sensor showed an increased signal of almost 20% with increasing beam angle. Sensors Aurora 5DOF-610099, Aurora 5DOF-610157, and Aurora Micro 6DOF-610059 showed no significant angle dependance. The Aurora Micro 6DOF-610059 and Aurora 5DOF-610157 sensors' cable signal revealed no extra signal attenuation. The latter gives a smaller overall attenuation. Therefore, the Aurora 5DOF-610157 sensor is chosen to be part of the novel dosimeter construction. It has a jitter error (average standard deviation of each individual measurement) of ±0.06 mm and a reproducibility of ±0.008 mm. In the optimal operating range, the average positional uncertainty is less than 0.2 mm. Average angle errors are not higher than 1 . 1 ∘ . Conclusion It is feasible to integrate an EM tracking sensor to a plastic scintillation dosimeter with minimal impact to the collected signal as well as sufficient positional accuracy to keep dose uncertainty below 5%.

Purpose High dose rate brachytherapy applies intense and destructive radiation. A treatment plan defines radiation source dwell positions to avoid irradiating healthy tissue. The study discusses methods to quantify any positional changes of source locations along the various treatment sessions. Methods Electromagnetic tracking (EMT) localizes the radiation source during the treatment sessions. But in each session the relative position of the patient relative to the filed generator is changed. Hence, the measured dwell point sets need to be registered onto each other to render them comparable. Two point set registration techniques are compared: a probabilistic method called coherent point drift (CPD) and a multidimensional scaling (MDS) technique. Results Both enable using EMT without external registration and achieve very similar results with respect to dwell position determination of the radiation source. Still MDS achieves smaller grand average deviations (CPD-rPSR: MD = 2.55 mm, MDS-PSR: MD = 2.15 mm) between subsequent dwell position determinations, which also show less variance (CPD-rPSR: IQR = 4 mm, MDS-PSR: IQR = 3 mm). Furthermore, MDS is not based on approximations and does not need an iterative procedure to track sensor positions inside the implanted catheters. Conclusion Although both methods achieve similar results, MDS is to be preferred over rigid CPD while nonrigid CPD is unsuitable as it does not preserve topology.

Purpose To evaluate the possibility of utilizing the high-dose rate (HDR) 169Yb and 60Co sources, in addition to 192Ir, for the treatment of skin malignancies with conical applicators. Methods Monte Carlo (MC) simulations were used to benchmark the dosimetric parameters of single 169Yb (4140), 60Co (Co0.A86), and 192Ir (mHDR-V2) brachytherapy sources in a water phantom and compared their results against published data. A standard conical tungsten alloy Leipzig-style applicator (Stand.Appl) was used for determination of the dose distributions at various depths with a single dwell position of the HDR sources. The HDR sources were modeled with its long axis parallel to the treatment plane within the opening section of the applicator. The source-to-surface distance (SSD) was 1.6 cm, which included a 0.1 cm thick removable plastic end-cap used for clinical applications. The prescription depth was considered to be 0.3 cm in a water phantom following the definitions in the literature for this treatment technique. Dose distributions generated with the Stand.Appl and the 169Yb and 60Co sources have been compared with those of the 192Ir source, for the same geometry. Then, applicator wall thickness for the 60Co source was increased (doubled) in MC simulations in order to minimize the leakage dose and penumbra to levels that were comparable to that from the 192Ir source. For each source-applicator combination, the optimized plastic end-cap dimensions were determined in order to avoid over-dosage to the skin surface. Results The normalized dose profiles at the prescription depth for the 169Yb-Stand.Appl and the 60Co-double-wall applicator were found to be similar to that of the 192Ir-Stand.Appl, with differences 2 cm from the applicator surface was

Purpose: High dose rate brachytherapy (HDR-BT) is widely used to treat gynecologic, anal, prostate, head, neck, and breast cancers. These treatments are typically administered in large dose per fraction (>5 Gy) and with high-gradient-dose-distributions, with serious consequences in case of a treatment delivery error (e.g., on dwell position and dwell time). Thus, quality assurance (QA) or quality control (QC) should be systematically and independently implemented. This paper describes the design and testing of a phantom and an instrumented gynecological applicator for pretreatment QA and in vivo QC, respectively. Methods: The authors have designed a HDR-BT phantom equipped with four GaN-based dosimeters. The authors have also instrumented a commercial multichannel HDR-BT gynecological applicator by rigid incorporation of four GaN-based dosimeters in four channels. Specific methods based on the four GaN dosimeter responses are proposed for accurate determination of dwell time and dwell position inside phantom or applicator. The phantom and the applicator have been tested for HDR-BT QA in routine over two different periods: 29 and 15 days, respectively. Measurements in dwell position and time are compared to the treatment plan. A modified position–time gamma index is used to monitor the quality of treatment delivery. Results: The HDR-BT phantom and the instrumented applicator have been used to determine more than 900 dwell positions over the different testing periods. The errors between the planned and measured dwell positions are 0.11 ± 0.70 mm (1σ) and 0.01 ± 0.42 mm (1σ), with the phantom and the applicator, respectively. The dwell time errors for these positions do not exhibit significant bias, with a standard deviation of less than 100 ms for both systems. The modified position–time gamma index sets a threshold, determining whether the treatment run passes or fails. The error detectability of their systems has been evaluated through tests on intentionally introduced error protocols. With a detection threshold of 0.7 mm, the error detection rate on dwell position is 22% at 0.5 mm, 96% at 1 mm, and 100% at and beyond 1.5 mm. On dwell time with a dwell time threshold of 0.1 s, it is 90% at 0.2 s and 100% at and beyond 0.3 s. Conclusions: The proposed HDR-BT phantom and instrumented applicator have been tested and their main characteristics have been evaluated. These systems perform unsupervised measurements and analysis without prior treatment plan information. They allow independent verification of dwell position and time with accuracy of measurements comparable with other similar systems reported in the literature.

Purpose: The aims of this study were (i) to design a new high-dose-rate (HDR) brachytherapy applicator for treating surface lesions with planning target volumes larger than 3 cm in diameter and up to 5 cm in size, using the microSelectron-HDR or Flexitron afterloader (Elekta Brachytherapy) with a 192Ir source; (ii) to calculate by means of the Monte Carlo(MC) method the dose distribution for the new applicator when it is placed against a water phantom; and (iii) to validate experimentally the dose distributions in water. Methods: The penelope2008MC code was used to optimize dwell positions and dwell times. Next, the dose distribution in a water phantom and the leakage dose distribution around the applicator were calculated. Finally, MC data were validated experimentally for a 192Ir mHDR-v2 source by measuring (i) dose distributions with radiochromic EBT3 films (ISP); (ii) percentage depth–dose (PDD) curve with the parallel-plate ionization chamber Advanced Markus (PTW); and (iii) absolute dose rate with EBT3 films and the PinPoint T31016 (PTW) ionization chamber. Results: The new applicator is made of tungsten alloy (Densimet) and consists of a set of interchangeable collimators. Three catheters are used to allocate the source at prefixed dwell positions with preset weights to produce a homogenous dose distribution at the typical prescription depth of 3 mm in water. The same plan is used for all available collimators. PDD, absolute dose rate per unit of air kerma strength, and off-axis profiles in a cylindrical water phantom are reported. These data can be used for treatment planning. Leakage around the applicator was also scored. The dose distributions, PDD, and absolute dose rate calculated agree within experimental uncertainties with the doses measured: differences of MC data with chamber measurements are up to 0.8% and with radiochromic films are up to 3.5%. Conclusions: The new applicator and the dosimetric data provided here will be a valuable tool in clinical practice, making treatment of large skin lesions simpler, faster, and safer. Also the dose to surrounding healthy tissues is minimal.

Purpose: In high dose rate brachytherapy (HDR-B), actual catheter reconstruction protocols are slow and errors prompt. The purpose of this study was to evaluate the accuracy and robustness of an electromagnetic (EM) tracking system for improved catheter reconstruction in HDR-B protocols. Methods: For this proof-of-principle, a total of 10 catheters were inserted in gelatin phantoms with different trajectories. Catheters were reconstructed using a Philips-design 18G biopsy needle (used as an EM stylet) and the second generation Aurora Planar Field Generator from Northern Digital Inc. The Aurora EM system exploits alternating current technology and generates 3D points at 40 Hz. Phantoms were also scanned using a μCT (GE Healthcare) and Philips Big Bore clinical CT system with a resolution of 0.089 mm and 2 mm, respectively. Reconstructions using the EM stylet were compared to μCT and CT. To assess the robustness of the EM reconstruction, 5 catheters were reconstructed twice and compared. Results: Reconstruction time for one catheter was 10 seconds or less. This would imply that for a typical clinical implant of 17 catheters, the total reconstruction time would be less than 3 minutes. When compared to the μCT, the mean EM tip identification error was 0.69 ± 0.29 mmmore » while the CT error was 1.08 ± 0.67 mm. The mean 3D distance error was found to be 0.92 ± 0.37 mm and 1.74 ± 1.39 mm for the EM and CT, respectively. EM 3D catheter trajectories were found to be significantly more accurate (unpaired t-test, p < 0.05). A mean difference of less than 0.5 mm was found between successive EM reconstructions. Conclusion: The EM reconstruction was found to be faster, more accurate and more robust than the conventional methods used for catheter reconstruction in HDR-B. This approach can be applied to any type of catheters and applicators. We would like to disclose that the equipments, used in this study, is coming from a collaboration with Philips Medical.« less

Purpose: High dose rate (HDR) brachytherapy is a treatment method that is used increasingly worldwide. The development of a sound quality assurance program for the verification of treatment deliveries can be challenging due to the high source activity utilized and the need for precise measurements of dwell positions and times. This paper describes the application of a novel phantom, based on a 2D 11 × 11 diode array detection system, named “magic phantom” (MPh), to accurately measure plan dwell positions and times, compare them directly to the treatment plan, determine errors in treatment delivery, and calculate absorbed dose. Methods: The magic phantom system was CT scanned and a 20 catheter plan was generated to simulate a nonspecific treatment scenario. This plan was delivered to the MPh and, using a custom developed software suite, the dwell positions and times were measured and compared to the plan. The original plan was also modified, with changes not disclosed to the primary authors, and measured again using the device and software to determine the modifications. A new metric, the “position–time gamma index,” was developed to quantify the quality of a treatment delivery when compared to the treatment plan. The MPh was evaluated to determine the minimum measurable dwell time and step size. The incorporation of the TG-43U1 formalism directly into the software allows for dose calculations to be made based on the measured plan. The estimated dose distributions calculated by the software were compared to the treatment plan and to calibrated EBT3 film, using the 2D gamma analysis method. Results: For the original plan, the magic phantom system was capable of measuring all dwell points and dwell times and the majority were found to be within 0.93 mm and 0.25 s, respectively, from the plan. By measuring the altered plan and comparing it to the unmodified treatment plan, the use of the position–time gamma index showed that all modifications made could be readily detected. The MPh was able to measure dwell times down to 0.067 ± 0.001 s and planned dwell positions separated by 1 mm. The dose calculation carried out by the MPh software was found to be in agreement with values calculated by the treatment planning system within 0.75%. Using the 2D gamma index, the dose map of the MPh plane and measured EBT3 were found to have a pass rate of over 95% when compared to the original plan. Conclusions: The application of this magic phantom quality assurance system to HDR brachytherapy has demonstrated promising ability to perform the verification of treatment plans, based upon the measured dwell positions and times. The introduction of the quantitative position–time gamma index allows for direct comparison of measured parameters against the plan and could be used prior to patient treatment to ensure accurate delivery. C 2015 American Association of Physicists in Medicine.

Purpose: To investigate the use of optically stimulated luminescent dosimeters (OSLDs) for high dose rate (HDR) Ir‐192 brachytherapy. While common in megavoltage radiotherapy applications, the performance of OSLDs using kilovoltage energies, high dose gradient and high dose rate regions ubiquitous to HDR has not been demonstrated. Methods: Commercially available nanoDotTM (Landauer, Glenwood, IL) OSLDs ‐ 5mm diameter and 0.2mm thickness ‐ were irradiated using an Ir‐192 source in various geometries to determine dose rate dependence. Angular geometries were created using a circular applicator designed for accelerated partial breast irradiation by Accuboost®. Results: Response remained linear for high doses and was independent of dose rate. Specifically, the OSLDs were shown to be linear with dose up to 200 cGy then became slightly supra‐linear up to 600 cGy. There was a slight angular dependence for OSLDs which becomes significant in ‘edge‐on’ scenarios. An asymmetry in this angular dependence was discovered, but was attributed to cable curvature, point source approximation, and positioning within its plastic casing. Conclusions: Clinical HDR doses of 300 cGy fall within the linear, dose‐rate‐independent region. Angular independence can be maintained by avoiding extreme ‘edge‐on’ measurement geometries. Because of re‐ readability, OSLDs can serve as a permanent record or alternatively be annealed within a few hours using conventional fluorescent light. Lastly, OSLDs are produced for only $5 each. Due to these features, in conjunction with the dosimetric performance, OSLDs should be considered a reliable tool for in vivo HDR brachytherapy measurements.

Purpose: To determine the optimal location of catheters in multichannel vaginal applicators to appropriately cover the vaginal cuff target and minimize dose to the organs at risk (OARs) and hot spots in the target. Methods: A new multichannel vaginal applicator with a diameter of 30 mmconsists of a single central catheter and an outer array of eight catheters. A total of 20 plans were generated from 5 patients by using different outer catheter locations at r = 4, 8, and 12 mm. The target was defined as a 5 mmcircumferential shell extending 4 cm in length around the applicator, excluding the bladder, rectum, and bowel. An inverse planning simulated annealing algorithm and graphical optimization was applied to ensure the prescription dose (7.0 Gy per fraction) covered >97% of the target and minimized dose to the OARs. Target coverage (D90 and V100), hot spots (V150 and V200), and OAR doses (D0.1cc, D1cc, and D2cc) from the various catheter placements were compared to single catheter plans. Results: By study design all plans had the same target coverage D90 (105.0– 108.3%) and V100 (97.1–97.2%). The V150 and V200 were 16.1% and 3.4% (r=0mm), 17.3% and 4.2% (r=4mm), 20.1% and 2.2% (r=8mm), and 30.1% and 6.0% (r=12mm). The DO.1cc to the OARs from the various catheter placements at r = 4, 8, and 12 mm was reduced by 4.0%, 8.6%, 11.9% (bladder), 7.4%, 13.2%, and 17.4% (rectum), when compared to the central catheter plans. Conclusions: Multichannel vaginal applicators provide better dosimetry than single channel applicator. The catheter array located closest to the applicator surface most significantly reduces dose tothe OARs at the expense of larger hot spots in the target. The array in the middle of the applicator radius provides significantly decreased dose to the OARs and gave relatively smaller hot spots.

Purpose: The RADPOS in vivo dosimetry system combines an electromagnetic positioning sensor with MOSFETdosimetry, allowing for simultaneous online measurements of dose and spatial position. In this work, we assess the potential use of RADPOS for measurements of motion and dose during prostate HDR brachytherapy.Methods: The RADPOS was positioned in the centre of a thin plastic tube supported by two parallel acrylic plates submerged in water. The detector was calibrated by sending an Ir‐192 source into an adjacent tube, to positions ranging from 8.0 to −8.0 cm along the vertical axis in increments of 0.5 cm. The dwell time at each position was 20 s and the change in threshold voltage of the RADPOS dosimeter was recorded for each position. The expected dose for each source position was calculated and compared to RADPOS measurements to obtain a detectorcalibration coefficient (cGy/mV). The procedure was then repeated sending the Ir‐192 source into 5 other tubes, located 1 to 10 cm away from the RADPOS. Source positions, dwell times, and position of the RADPOS detector were the same as for the calibration. The dose for each source position was determined by RADPOS measurements and calibration coefficient and compared to the expected dose.Results: An average calibration coefficient of 0.74±0.11 cGy/mV was calculated for RADPOS measurements of Ir‐192 irradiations. The absolute difference between RADPOS values and expected dose for subsequent measurements averaged over all source positions was 0.7±5.4 cGy. Conclusions: In vivo dosimetry can potentially signal errors in catheter placement or numbering before entire dose is delivered. The demonstrated accuracy of RADPOS dose measurements and its ability to simultaneously measure displacement makes it a powerful tool for HDR brachytherapy treatments for prostate cancer, where high dose gradients and movement of the prostate gland can present unique in vivo dosimetry challenges. Financial and technical support has been received from Best Medical Canada and Ascension Technology Corporation.

Treatment of cervical cancer often involves intracavitary high dose rate (HDR) brachytherapy. Dose delivered to the bladder and rectum are typically estimated using the ICRU reference points. Dose to the sigmoid and small bowel are not estimated, yet these organs typically exhibit significant complication rates. The objective of this study was to estimate dose to the small bowel and sigmoid using CT images. Bladder and rectum dose estimates obtained from the reference point method were also compared to those obtained from CT images. Eighteen CT scans taken before or after treatment of women treated with HDR using ring and tandem applicators were included in this study. The small bowel, sigmoid, bladder and rectum were contoured and the ICRU points were digitized. The minimum dose to 2cc (D2cc ) of each organ was calculated and normalized to % prescribed to Point A. Average D2cc bowel dose was 70%. D2cc bowel dose was significantly higher than both D2cc rectal (27%) and D2cc sigmoid (31%) doses. The average D2cc bladder and rectal doses were 68% (p=NS) and 27% (p

The feasibility of using cone beam computed tomography(CBCT)images for Monte Carlo (MC)brachytherapydose calculations has been investigated. To evaluate the effects of tissue heterogeneities and finite patient dimensions for 192 Ir high dose rate treatment, CT‐based MC calculations for breast and head and neck cases were first performed using the PTRAN_CT photon transport code. PTRAN_CT is an accelerated MC code specifically designed for patient‐specific dose calculations. Muscles and adipose tissues, which are nearly indistinguishable in CBCTimages, are found to cause minimal dose perturbations at 192 Ir energies compared to water. The proximity of the tumor to the skin, however, will have an observable impact on the dose up to a few percent. Therefore, for CBCT calculations, a reasonable assignment of material and density values to the patient voxel geometry, with a good delineation of the skin and bony structures, will suffice for MCdose calculations. A CBCT‐based calculation for an actual treatment plan with the tumor close to the cheek was performed. The results were compared to TG43 calculations to quantify the dose differences in the target and critical structures. Since the dose delivered to the tumor is mostly primary dose, deviations are found mostly in the organs at risk where scatter contribution becomes more significant. This study shows that for HDR brachytherapy applications, CBCT‐based MC calculations is a feasible option despite inferior image quality and larger uncertainties in the Hounsfield Units compared to CTimages. Research supported by Nucletron BV.

Purpose: To establish the accuracy and speed ofbGPUMCD, a GPU-oriented Monte Carlo code used for high dose rate brachytherapydose calculations. The first objective is to evaluate the time required for dose calculation when full Monte Carlo generated dose distribution kernels are used for plan optimization. The second objective is to assess the accuracy and speed when recalculating pre-optimized plans, consisting of many dwell positions. Methods: bGPUMCD is tested with three clinical treatment plans : one prostate case, one breast case, and one rectum case with a shielded applicator. Reference distributions, generated with GEANT4, are used as a basis of comparison. Calculations of full dose distributions of pre-optimized treatment plans as well as single dwell dosimetry are performed. Single source dosimetry, based on TG-43 parameters reproduction, is also presented for the microSelectron V2 (Nucletron, Veenendaal, The Netherlands). Results: In timing experiments, the computation of single dwell position dose kernels takes between 0.25 and 0.5 s.bGPUMCD can compute full dose distributions of previously optimized plans in ∼2 s. bGPUMCD is capable of computing pre-optimized brachytherapy plans within 1% for the prostate case and 2% for the breast and shielded applicator cases, when comparing the dosimetric parameters D90 and V100 of the reference (GEANT4) and bGPUMCDdistributions. For all voxels within the target, an absolute average difference of approximately 1% is found for the prostate case, less than 2% for the breast case and less than 2% for the rectum case with shielded applicator. Larger point differences (>5%) are found within bony regions in the prostate case, where bGPUMCD underdoses compared to GEANT4. Single source dosimetry results are mostly within 2% for the radial function and within 1%–4% for the anisotropic function. Conclusions: bGPUMCD has the potential to allow for fast MCdose calculation in a clinical setting for all phases of HDR treatment planning, from dose kernel calculations for plan optimization to plan recalculation.

Purpose: To quantify movement of prostate cancer patients undergoing treatment, using an in-house developed motion sensor in order to determine a relationship between patient movement and high dose rate (HDR) brachytherapy implant displacement. Methods: An electronic motion sensor was developed based on a three axis accelerometer. HDR brachytherapy treatment for prostate is delivered at this institution in two fractions 24 h apart and 22 patients were monitored for movement over the interval between fractions. The motion sensors functioned as inclinometers, monitoring inclination of both thighs, and the inclination and roll of the abdomen. The implanted HDR brachytherapy catheter set was assessed for displacement relative to fiducial markers in the prostate. Angle measurements and angle differences over a 2 s time base were binned, and the standard deviations of the resulting frequency distributions used as a metric for patient motion in each monitored axis. These parameters were correlated to measured catheter displacement using regression modeling. Results: The mean implant displacement was 12.6 mm in the caudal direction. A mean of 19.95 h data was recorded for the patient cohort. Patients generally moved through a limited range of angles with a mean of the exception of two patients who spent in excessmore » of 2 h lying on their side. When tested for a relationship between movement in any of the four monitored axes and the implant displacement, none was significant. Conclusions: It is not likely that patient movement influences HDR prostate implant displacement. There may be benefits to patient comfort if nursing protocols were relaxed to allow patients greater freedom to move while the implant is in situ.« less

Purpose: The purpose of this work was to develop a quality assurance (QA) tool for high-dose-rate (HDR) brachytherapy that would quickly and easily verify both source positioning (dwell positions) and durations (dwell times). Methods: The authors constructed a QA tool that combined radiochromic film to verify position with four photodiodedetectors to verify dwell times. To characterize the temporal accuracy of the tool, a function generator powered four red light-emitting diodes that were optically coupled to the four photodiodedetectors. The QA tool was used to verify the dwell positions and times of a commercial brachytherapy afterloader. Measurements of dwell time were independently verified by a one-dimensional optical camera that acquired 1000 lines/s. Results: The temporal accuracy of the QA tool was found to be about 1 ms. For visual assessment, the source position could be located within about 0.5 mm. Evaluating the accuracy and precision of an HDR brachytherapy afterloader, the authors found that the bias in dwell time can exceed 60 ms and the dwell time associated with the first dwell position had an unexpectedly large standard deviation of 30 ms. They found that the source locations were much easier to locate on the film if a plastic catheter was used instead of a metal treatment tube. Scanning the films enabled the dwell positions to be determined within about 0.2 mm. Conclusions: For pretreatment QA, the authors found that this tool allowed verification of dwell positions and dwell times in about 6 min.

Purpose: The purpose of this work is to calculate two-dimensional (2D) dose rate distributions around the BEBIG (Eckert and Ziegler, BEBIG GmbH, Germany) models GK60M21 (old) and Co0.A86 (new) {sup 60}Co high dose rate brachytherapy sources in an unbounded liquid water phantom. The study includes calculation of absorbed dose to water-kerma ratio D/K around the BEBIG sources and a {sup 60}Co point source in water. A comparison is made with previously published data. Methods: The EGSnrcMP Monte Carlo code system is used to calculate the absorbed dose and water-kerma in water and air-kerma strength in vacuum. EGSnrcMP-based user codes such as EDKnrc, FLURZnrc, and DOSRZnrc are employed in the work. Results: The value of D/K reaches a maximum of 1.040{+-}0.002 for the {sup 60}Co point source (constant between 3.6 and 4.5 mm from the source) and 1.076{+-}0.002 for the BEBIG sources (constant between 2.6 and 3.2 mm along the transverse axis of the sources). Dose rate data for the new and old sources are comparable to published data for radial distances r>0.5 cm. Differences up to 9% are observed at points close to the source (r=0.25 cm). In addition for the new source, compared to previously published data, dose ratemore » data are higher by 14% along the longitudinal axis where the source cable is connected. Dose rate differences on the longitudinal axis ({theta}=180 deg.) of this source are explained by varying the length of the simulated source cable. Conclusions: The 2D rectangular data set calculated in the present work could be considered for quality control on radiotherapy treatment planning systems.« less

When treating prostate cancer using high dose rate (HDR) brachytherapy, overdosing the rectal wall may lead to post-treatment rectal complications. An area of concern is related to how the rectal wall dose is calculated by treatment planning systems (TPSs). TPSs are used to calculate the dose delivered to the rectal wall, but they assume that the rectum is a water-equivalent homogeneous medium of infinite size and do not consider the effect that an air-filled “empty” rectal cavity would have on the dose absorbed along the rectal wall. The aim of this research is to quantify the effect that an air cavity has on the rectal wall dose, as its presence changes the backscatter conditions in the region. The MO Skin and RADFET dosimeters proved capable of measuring absolute dose with increasing distance from the HDR Ir-192 brachytherapy source. However, the anterior rectal wall doses measured by the MOSkin and RADFET in an empty rectal cavity were 14.7 ± 0.2 % and 13.7 ± 0.6 % lower than the dose measured in a homogeneous rectal phantom. Monte Carlo simulations corroborated the experimentally obtained results, reporting a − 13.2 ± 0.6 % difference. The dose measured at the posterior wall of an empty rectal cavity was between 22% and 26% greater than the dose measured in a full rectal cavity. The heterogeneity of the rectal volume appears to have a significant effect on the rectal dose when compared to calculated rectal dose.

High dose rate brachytherapy (HDR-BT) is one of the many modalities for prostate cancer treatment. Due to the nature of HDR-BT, in vivo dosimetry is feasible and can be used to verify consistent dose delivery. In order to validate a dose verification system for HDR-BT prostate cancer treatment, a radiophotoluminescent glass dosimeter (RPLGD) was used and the measurements were compared with those from a thermoluminescent dosimeter. The RPLGD shows many advantages in HDR-BT dose measurement, such as repeatability, stability, and small effective size. These advantages make the RPLGD a superior option for use as a dosimeter in HDR-BT. The results described here show that the difference between the measured dose and the treatment planned dose is less than 5%. A Monte Carlo simulation for the dose was performed using Monte Carlo N -particle to investigate position error. This study concludes that the RPLGD is a promising and reliable dosimeter for HDR-BT in vivo dosimetry with clinically acceptable accuracy.

The increased demand for high dose rate (HDR) brachytherapy as an alternative to external beam radiotherapy has led to the introduction of a HDR brachytherapy isotope Yb 169 . This source offers a dose rate similar to Ir 192 HDR sources, at about one fourth the effective photon energy. This work presents the calibration of this source in terms of air-kerma strength, based on an adaptation of the current, National Institute of Standards and Technology traceable, in air measurement technique currently used for Ir 192 HDR sources. Several additional measurement correction factors were required, including corrections for air scatter, air attenuation, and ion recombination. A new method is introduced for determining the ion chambercalibration coefficient N k Yb 169 . An uncertaintyanalysis was also performed, indicating an overall measurement expanded uncertainty in the air-kerma strength ( k = 2 ) of 2.2%.

Fractionated high dose rate endorectal brachytherapy (HDR-EBT) using CT-based treatment planning is an alternative method for preoperative down-sizing and down-staging of advanced rectal adeno-carcinomas. The authors present an image guidance procedure that was developed to ensure daily dose reproducibility for the four brachytherapy treatment fractions. Since the applicator might not be placed before each treatment fraction inside the rectal lumen in the same manner as it was placed during the 3D CT volume acquisition used for treatment planning, there is a shift along the catheter axis that may have to be performed. The required shift is determined by comparison of a daily radiograph with the treatment planning digitally-reconstructed radiograph (DRR). A procedure is developed for DRR reconstruction from the 3D data set used for the treatment planning, and two possible daily longitudinal shifts are illustrated: above and below the planning dose distribution. The authors also describe the procedure for rotational alignment illustrated on a clinical case. Reproduction of the treatment planned dose distribution on a daily basis is crucial for the success of fractionated 3D based brachytherapy treatments. Due to the cylindrical symmetry of the applicator used for preoperative HDR-EBT, two types of adjustments are necessary: applicator rotation and dwellmore » position shift along the applicator's longitudinal axis. The impact of the longitudinal applicator shift prior to treatment delivery for 62 patients treated in our institution is also assessed.« less

The purpose of this study is to obtain the dosimetric parameters of a new Co-60 source used in high dose rate brachytherapy and manufactured by BEBIG (Eckert & Ziegler BEBIG GmbH, Germany). The Monte Carlo method has been used to obtain the dose rate distribution in the updated TG-43U1 formalism of the American Association of Physicists in Medicine. In addition, to aid the quality control process on treatment planning systems (TPS), a two-dimensional rectangular dose rate table, coherent with the TG-43U1 dose calculation formalism, is given. These dosimetric data sets can be used as input data of the TPS calculations and to validate them.

The feasibility of a recently designed metal-oxide-semiconductor field effect transistor (MOSFET) dosimetry system for dose verification of high dose rate (HDR) brachytherapy treatment planning was investigated. MOSFET detectors were calibrated with a 0.6 cm3 NE-2571 Farmer-type ionization chamber in water. Key characteristics of the MOSFET detectors, such as the energy dependence, that will affect phantom measurements with HDR 192Ir sources were measured. The MOS-FET detector was then applied to verify the dosimetric accuracy of HDR brachytherapy treatments in a custom-made water phantom. Three MOSFET detectors were calibrated independently, with the calibration factors ranging from 0.187 to 0.215 cGy/mV. A distance dependent energy response was observed, significant within 2 cm from the source. The new MOSFET detector has a good reproducibility (

The MCNP5 Monte Carlo code was used to simulate the dosimetry of an M-19 iridium-192 high dose rate brachytherapy source in both air/vacuum and water environments with the in-air photon spectrum filtered to remove low-energy photons below delta=10 keV. Dosimetric data was organized into an away-along table and was used to derive the updated AAPM Task Group Report No. 43 (TG-43U1) parameters including S(K), D(r, theta), lamda, gL(r), F(r, theta), phi an(r), and phi an, and their respective statistical uncertainties.

An ytterbium-169 high dose rate brachytherapy source, distinguished by an intensity-weighted average photon energy of 92.7 keV and a 32.015{+-}0.009 day half-life, is characterized in terms of the updated AAPM Task Group Report No. 43 specifications using the MCNP5 Monte Carlo computer code. In accordance with these specifications, the investigation included Monte Carlo simulations both in water and air with the in-air photon spectrum filtered to remove low-energy photons below 10 keV. TG-43 dosimetric data including S{sub K}, D(r,{theta}), {lambda}, g{sub L}(r), F(r,{theta}), {phi}{sub an}(r), and {phi}{sub an} were calculated and statistical uncertainties in these parameters were derived and calculated in the appendix.

For the purpose of evaluating the use of Yb 169 for prostate High Dose Rate brachytherapy (HDR), a hypothetical Yb 169 source is assumed with the exact same design of the new microSelectron source replacing the Ir 192 active core by pure Yb 169 metal.Monte Carlo simulation is employed for the full dosimetric characterization of both sources and results are compared following the AAPM TG-43 dosimetric formalism. Monte Carlo calculated dosimetry results are incorporated in a commercially available treatment planning system ( SWIFT TM ) , which features an inverse treatment planning option based on a multiobjective dose optimization engine. The quality of prostate HDR brachytherapy using the real Ir 192 and hypothetical Yb 169 source is compared in a comprehensive analysis of different prostate implants in terms of the multiobjective dose optimization solutions as well as treatment quality indices such as Dose Volume Histograms (DVH) and the Conformal Index (COIN). Given that scattering overcompensates for absorption in intermediate photon energies and distances in the range of interest to prostate HDR brachytherapy, Yb 169 proves at least equivalent to Ir 192 irrespective of prostate volume. This has to be evaluated in view of the shielding requirements for the Yb 169 energies that are minimal relative to that for Ir 192 .

Purpose: The purpose of this work is to develop a new applicator for administering high dose rate (HDR) brachytherapy using 3D printing technology. Primary advantages of using a 3D printed applicator will be to offer a more streamlined approach for therapists and patients while achieving better conformity, reproducibility, and patient specific applicators. Methods: A phantom study was conducted to measure the effectiveness of a 3D printed surface applicator by analyzing tumours on three locations of the body: the foot, nose, and scalp. The applicator was designed using Eclipse and further modified using Blender to create the catheter tunnels before being printed on a Lulzbot Taz 5 3D printer. A radiation plan was made using Oncentra Brachytherapy for a control treatment option using Freiburg Flaps and one with the novel method of a 3D printed applicator. A comparative analysis was made using D90, D100, V100, V150, and V200 Results: The 3D printed applicator showed comparable dose coverage with significant improvements on highly irregular surfaces when analyzed against a plan made using Freiburg Flaps. Although both plans exhibited complete tumour coverage, the 3D applicator showed improvements in D90 and V150 and the 3D applicator had a dose homogeneity index (DHI) of 0.99 compared to a DHI of 0.97 for the control. Therapist prep time also dropped significantly due to the lack of need for a thermoplastic mesh. Conclusions: 3D printed applicators for treatment of superficial sites proved to offer more patient convenience, less prep time, better conformity and tighter margins.

Purpose: To evaluate the improvement in plan quality when various combinations of 192Ir, 60Co, and 169Yb sources are used in combination with a novel direction modulated brachytherapy (DMBT) tandem applicator for high dose rate brachytherapy of cervical cancer. Methods: The proposed DMBT tandem applicator is designed for image-guided adaptive brachytherapy (IGABT), especially MRI, of cervical cancer. It has 6 peripheral holes of 1.3-mm width, grooved along a 5.4-mm diameter nonmagnetic tungsten alloy rod of density 18.0 g/cc, capable of generating directional dose profiles - leading to enhanced dose sculpting capacity through inverse planning. Monte Carlo simulations of the three HDR sources individually inside the DMBT applicator were performed and imported into an in-house developed inverse optimization code. We then performed inverse planning with 14 cervical cancer patients enrolled in EMBRACE study. In all patients, 3D MRI-based planning was performed while utilizing 1) tandem-ring and needles attached-to-ring (7 patients) and 2) tandem-ring and needles both attached-to-ring and free-hand-loaded (7 patients), in accordance with the GEC-ESTRO recommendations. All plans were normalized to receive the same HRCTV D90 and DVH parameters were evaluated. Results: The DMBT tandem was used in all cases. Overall, the combined use of two sources (192Ir-60Co and 192Ir-169Yb, but not 60Co-169Yb) generally produced better quality plans than with the 192Ir source alone in terms of sparing OARs. For example, up to 3.5, 4.4, and 3.9% individual reductions in D2cc were observed for the bladder, rectum, and sigmoid, respectively, between 192Ir-60Co and 192Ir-only plans for patient cases in #1. While up to 5.5, 2.0, and 5.7% individual reductions were observed for patient cases in #2. Conclusion: We have demonstrated that, in addition to “directional modulation” of DMBT, use of multiple sources with sufficient differences in energy can be utilized to achieve additional improvement in plan quality for IGABT of cervical cancer.

Purpose: To investigate quantitatively the accuracy of dose distributions for the Ir-192 high-dose-rate (HDR) brachytherapy source calculated by the Brachytherapy-Planning system (BPS) and measured using a multiple-array-diode-detector in a heterogeneous medium. Methods: A two-dimensional diode-array-detector system (MapCheck2) was scanned with a catheter and the CT-images were loaded into the Varian-Brachytherapy-Planning which uses TG-43-formalism for dose calculation. Treatment plans were calculated for different combinations of one dwell-position and varying irradiation times and different-dwell positions and fixed irradiation time with the source placed 12mm from the diode-array plane. The calculated dose distributions were compared to the measured doses with MapCheck2 delivered by an Ir-192-source from a Nucletron-Microselectron-V2-remote-after-loader. The linearity of MapCheck2 was tested for a range of dwell-times (2–600 seconds). The angular effect was tested with 30 seconds irradiation delivered to the central-diode and then moving the source away in increments of 10mm. Results: Large differences were found between calculated and measured dose distributions. These differences are mainly due to absence of heterogeneity in the dose calculation and diode-artifacts in the measurements. The dose differences between measured and calculated due to heterogeneity ranged from 5%–12% depending on the position of the source relative to the diodes in MapCheck2 and different heterogeneities in the beam path. The linearity test of the diode-detector showed 3.98%, 2.61%, and 2.27% over-response at short irradiation times of 2, 5, and 10 seconds, respectively, and within 2% for 20 to 600 seconds (p-value=0.05) which depends strongly on MapCheck2 noise. The angular dependency was more pronounced at acute angles ranging up to 34% at 5.7 degrees. Conclusion: Large deviations between measured and calculated dose distributions for HDR-brachytherapy with Ir-192 may be improved when considering medium heterogeneity and dose-artifact of the diodes. This study demonstrates that multiple-array-diode-detectors provide practical and accurate dosimeter to verify doses delivered from the brachytherapy Ir-192-source.

High dose rate (HDR) 192 Ir sources are currently used in intravascular brachytherapy (IVB) for the peripheral arterial system. This poses a demand on evaluating accurate dose parameters in the near-source region for such sources. The purpose of this work is to calculate the dose parameters for the old VariSource HDR 192 Ir source and the new microSelectron HDR 192 Ir source, using Monte Carlo electron and photontransport simulation. The two-dimensional (2D) dose rate distributions and the air kerma strengths for the two HDR sources were calculated by EGSnrc and EGS4Monte Carlo codes. Based on these data, the dose parameters proposed in the AAPM TG-60 protocol were derived. The dose rate constants obtained are 13.119±0.028 cGy h −1 U −1 for the old VariSource source, and 22.751±0.031 cGy h −1 U −1 for the new microSelectron source at the reference point (r 0 =2 mm , θ=π/2). The 2D dose rate distributions, the radial dose functions, and the anisotropy functions presented for the two sources cover radial distances ranging from 0.5 to 10 mm. In the near-source region on the transverse plane, the doseeffects of the charged particle nonequilibrium and the beta-particle dose contribution were studied. It is found that at radial distances ranging from 0.5 to 2 mm, these effects increase the calculated dose rates by up to 29% for the old VariSource source, and by up to 12% for the new microSelectron source, which, in turn, change values of the radial dose function and the anisotropy function. The present dose parameters, which account for the charged particle nonequilibrium and the beta particle contribution, may be used for accurate IVB dose calculation.

Quantification of transit time of a remote after-loading high dose rate (HDR) brachytherapy source is important both for accurate treatment planning and for quality assurance checks. In this investigation, an HDR-1000 well ionization chamber and a precision electrometer are used to measure the transit time of the Ir-192 source of a Nucletron Micro-Selectron HDR brachytherapy unit. The charge generated both during source dwelling at a selected position in an endobronchial catheter inserted into the chamber and during source travel to this position from another location at a distance of 0.5 to 10 cm from it was measured. A linear regression analysis of the measured charge as a function of dwell time was made. The interdwell position transit time was calculated from the ratio of the charge intercept and the slope of the straight line obtained from the regression analysis. The values of the effective transit time, which is a combination of interdwell position transit time and dwell time error of the after-loading unit, were found to be 0.03 and 0.45 s for 0.5 and 10 cm separation between two dwell positions, respectively. The average time for 1 cm travel of the source between two dwell positions was found to be 0.022 s, resulting in an average speed of 45.5 cm/s. This simple procedure has the potential to be utilized for routine quality assurance check of the interdwell position transit time of any remote after-loading HDR brachytherapy source.

We investigated a pinhole imaging system for independent in vivo monitoring and verification of high dose rate (HDR) brachytherapy treatment. The system consists of a high-resolution pinhole collimator, an x-ray fluoroscope, and a standard radiographic screen-film combination. Autofluoroscopy provides real-time images of the in vivo Ir-192 HDR source for monitoring the source location and movement, whereas autoradiography generates a permanent record of source positions on film. Dual-pinhole autoradiographs render stereo-shifted source images that can be used to reconstruct the source dwell positions in three dimensions. The dynamic range and spatial resolution of the system were studied with a polystyrene phantom using a range of source strengths and dwell times. For the range of source activity used in HDR brachytherapy, a 0.5 mm diameter pinhole produced sharp fluoroscopic images of the source within the dynamic range of the fluoroscope. With a source-to-film distance of 35 cm and a 400 speed screen-film combination, the same pinhole yielded well recognizable images of a 281.2 GBq (7.60 Ci) Ir-192 source for dwell times in the typical clinical range of 2 to 400 s. This 0.5 mm diameter pinhole could clearly resolve source positions separated by lateral displacements as small as 1 mm. Using a simple reconstruction algorithm, dwell positions in a phantom were derived from stereo-shifted dual-pinhole images and compared to the known positions. The agreement was better than 1 mm. A preliminary study of a patient undergoing HDR treatment for cervical cancer suggests that the imaging method is clinically feasible. Based on these studies we believe that the pinhole imaging method is capable of providing independent and reliable real-time monitoring and verification for HDR brachytherapy.

An analytical Monte Carlo simulation code, incorporating in detail source construction and dimensions, was used to investigate the dosimetric characteristics of the VariSource 192 Ir high dose rate brachytherapysource.Dose-rate constant, radial dose functions, and anisotropy functions, utilized in the AAPM Task Group 43 dose estimation formalism, were calculated with the source centered in a spherical water phantom of 30 cm in diameter. The results, which are in agreement with the corresponding data available in the literature, are compared to those obtained in our previous study for the widely used microSelectron 192 Ir high dose-ratebrachytherapysource. The dose-rate constant was found to be equal to 1.043±0.005 cGy h−1 U−1 for the VariSource, compared to a value of 1.116±0.006 cGy h−1 U−1 calculated for the microSelectron. Significant differences in the anisotropy of the two sources are observed only for polar angles close to their long axis and are due to their different dimensions.

Purpose: Surface mold applicators can be customized to fit irregular skin surfaces that are difficult to treat with other radiation therapy techniques. Optimal design of customized HDR skin brachytherapy is not well-established. We evaluated the impact of applicator thickness (source to skin distance) on target dosimetry. Methods: 27 patients had 34 treated sites: scalp 4, face 13, extremity 13, and torso 4. Custom applicators were constructed from 5–15 mm thick thermoplastic bolus molded over the skin lesion. A planar array of plastic brachytherapy catheters spaced 5–10 mm apart was affixed to the bolus. CT simulation was used to contour the target volume and to determine the prescription depth. Inverse planning simulated annealing followed by graphical optimization was used to plan and deliver 40–56 Gy in 8–16 fractions. Target coverage parameters (D90, Dmean, and V100) and dose uniformity (V110–200, D0.1cc, D1cc, and D2cc) were studied according to target depth (

In this article we introduce a new high-intensity 192 Ir source design for use in a recently reengineered microSelectron-HDR remote afterloading device for high dose-rate (HDR) brachytherapy. The maximum rigid length and outer diameter of the new source are reduced to 4.95 and 0.90 mm, respectively, compared to 5.50 and 1.10 mm for the previous source design introduced in 1991. In addition, a smaller diameter and more flexible steel cable are used, allowing the source cable to negotiate smaller diameter catheters or more tortuously curved catheters. Using Monte Carlophotontransport simulation, the complete two-dimensional (2-D) dose-rate distribution is calculated over the 0.1–7 cm distance range and are presented both as conventional 2-D Cartesian lookup tables and in the formalism recommended by the American Association of Physicists in Medicine Task Group 43 (TG-43) Report. The dose distribution of this source is very similar to that of its predecessor, except near the source tip and in the shadow of the cable assembly, where differences of 5%–8% are apparent. The accuracy of various methods for extrapolating beyond the tabulated anisotropy functions to short distances is evaluated. It is demonstrated that linear extrapolation from the anisotropy functions defined by TG-43 accurately (±2%) estimates dose rate at short and long distances lying outside the radial distance range of the original measured data from which the anisotropy and radial dose functions were derived. In contrast, the algorithm used on the vendor’s planning system results in large calculation errors at distances less than 5 mm.

GAFChromic film has become increasingly popular for radiationdosimetry. In this study we explore the use of GAFChromic film as an in vivodosimeter for quality assurance (QA) of fractionated high dose rate 192 Ir treatments. Accuracy of dose distribution is explored for the simple vaginal cylinder geometry for which the dose can be easily calculated for comparison. Source dwell times for several patients were optimized to deliver 500 cGy at 0.5 cm from the surface of the vaginal cylinder applicator using a commercial treatment planning system. GAFChromic film was taped to the vaginal cylinder applicator and was enclosed in a leak proof rubber sleeve prior to its insertion. Optical densities were measured along the film at 2 mm spacing, using a densitometer with filtered red light. Density corrections for transient film darkening effects were made and optical densities were converted to absorbed dose in cGy. In vivo patient dose distribution measured for different patients and different fractions were compared with the calculated values along the applicator surface. The variation between the calculated and measureddose was ±10%. The reproducibility of dosemeasurement for different fractions was within ±5%. This study demonstrates the potential usefulness of the film as an in vivo for brachytherapy QA.

We have developed a system for source localization and real-time planning of interstitial volume implants for intraoperative radiation therapy (IORT) using high dose rate remote afterloading techniques. Source localization is realized by using an electromagnetic tracking device, which consists of a transmitter coil, a receiver coil, and a signal processing unit, to generate the coordinates and orientation of the receiver. A drawback of the device is its sensitivity to adjacent metallic objects. Localization accuracy was evaluated in an operating room environment, where the metallic objects closest to the receiver are surgical retractors (that, incidentally, preclude radiographic localization). For achievable separation distances, we found an rms error of 0.7 mm in determining the distance between points 2 cm apart, thereby demonstrating the feasibility of the method. The receiver is mounted on a plastic block from which projects a long stylet and the transmitter is located at about 50 cm from the receiver. The stylet is inserted sequentially into source catheters to obtain the location and orientation data that serve as input to treatment planning software. The planning program optimizes source dwell time to make calculated dose conform to the dose prescribed on an ellipsoidal surface to an extent consistent with a certain level of dose uniformity inside the target volume. A least squares method is used that involves minimizing the objective function by a matrix method (nonnegative least squares). We have demonstrated that dwell time optimization can be performed in a short time and that the approach is adequate for the IORT application.

An Eckert & Ziegler Bebig Co0.A86 cobalt 60 high dose rate (HDR) brachytherapy source was commissioned for clinical use. Long-lived Co-60 HDR sources offer potential logistical and economic advantages over Ir-192 sources, and should be considered for low to medium workload brachytherapy departments where modest increases in treatment times are not a factor. In optimized plans, the Co-60 source provides a similar dose distribution to Ir-192 despite the difference in radiation energy. By switching to Co-60, source exchange frequency can be reduced by a factor of 20, resulting in overall financial savings of more than 50% compared to Ir-192 sources. In addition, a reduction in Physicist QA workload of roughly 200 hours over the 5 year life of the Co-60 source is also expected. These benefits should be considered against the modest increases in average treatment time compared to those of Ir-192 sources, as well as the centre-specific needs for operating room shielding modification.

Purpose: To apply surface collimation for superficial flap HDR skin brachytherapy utilizing common clinical resources and to demonstrate the potential for OAR dose reduction within a clinically relevant setting. Methods: Two phantom setups were used. 3 mm lead collimation was applied to a solid slab phantom to determine appropriate geometries relating to collimation and dwell activation. The same collimation was applied to the temple of an anthropomorphic head phantom to demonstrate lens dose reduction. Each setup was simulated and planned to deliver 400 cGy to a 3 cm circular target to 3 mm depth. The control and collimated irradiations were sequentially measured using calibrated radiochromic films. Results: Collimation for the slab phantom attenuated the dose beyond the collimator opening, decreasing the fall-off distances by half and reducing the area of healthy skin irradiated. Target coverage can be negatively impacted by a tight collimation margin, with the required margin approximated by the primary beam geometric penumbra. Surface collimation applied to the head phantom similarly attenuated the surrounding normal tissue dose while reducing the lens dose from 84 to 68 cGy. To ensure consistent setup between simulation and treatment, additional QA was performed including collimator markup, accounting for collimator placement uncertainties, standoff distance verification, and in vivo dosimetry. Conclusions: Surface collimation was shown to reduce normal tissue dose without compromising target coverage. Lens dose reduction was demonstrated on an anthropomorphic phantom within a clinical setting. Additional QA is proposed to ensure treatment fidelity.

The data from Meisberger et al. [Radiology 90, 953-957 (1968)] are often used as a basis for dose calculations in brachytherapy. In order to describe the absorbed dose in water around a brachytherapy point source, Meisberger provided a polynomial fit for different isotopes taking into account the effect of attenuation and scattering. The validity of the Meisberger coefficients is restricted to distances up to 10 cm from the source, which is regarded to be satisfactory for most brachytherapy applications. However, for more distant organs it may lead to errors in calculated absorbed dose. For this reason dose measurements have been performed in air and in water around a high activity 60Co source used in high dose rate brachytherapy. Measurements were carried out to distances of 20 cm, using ionization chambers. These data show that at a distance of about 15 cm the amount of scattered radiation virtually equals the amount of primary radiation. This emphasizes the contribution of scattered radiation to the dose in healthy tissue far from the target volume, even with relatively high energy photon radiation of 60Co. It is also shown that the Meisberger data as well as the approach of Van Kleffens and Star [Int. J. Radiat. Oncol. Phys. 5, 557-563 (1979)] lead to significant errors in absorbed dose between distances of 10 and 20 cm from the source. In addition to these measurements, the Monte Carlo code has been used to calculate separately primary dose and scattered dose from a cobalt point source. The calculated results agree with the experimental data within 1% for a most distant dose scoring region.

Purpose: Accuracy of positioning, timing and activity is of critical importance for High Dose Rate (HDR) brachytherapy delivery. Respective measurements via film autoradiography, stop-watches and well chambers can be cumbersome, crude or lack dynamic source evaluation capabilities. To address such limitations, a single device radioluminescent detection system enabling automated real-time quantification of activity, position and timing accuracy is presented and experimentally evaluated. Methods: A radioluminescent sheet was fabricated by mixing Gd?O?S:Tb with PDMS and incorporated into a 3D printed device where it was fixated below a CMOS digital camera. An Ir-192 HDR source (VS2000, VariSource iX) with an effective active length of 5 mm was introduced using a 17-gauge stainless steel needle below the sheet. Pixel intensity values for determining activity were taken from an ROI centered on the source location. A calibration curve relating intensity values to activity was generated and used to evaluate automated activity determination with data gathered over 6 weeks. Positioning measurements were performed by integrating images for an entire delivery and fitting peaks to the resulting profile. Timing measurements were performed by evaluating source location and timestamps from individual images. Results: Average predicted activity error over 6 weeks was .35 ± .5%. The distance between four dwell positions was determined by the automated system to be 1.99 ± .02 cm. The result from autoradiography was 2.00 ± .03 cm. The system achieved a time resolution of 10 msec and determined the dwell time to be 1.01 sec ± .02 sec. Conclusion: The system was able to successfully perform automated detection of activity, positioning and timing concurrently under a single setup. Relative to radiochromic and radiographic film-based autoradiography, which can only provide a static evaluation positioning, optical detection of temporary radiation induced luminescence enables dynamic detection of position enabling automated quantification of timing with millisecond accuracy.