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Blood and urine are historically the most frequent matrices used for measuring chemical levels in human biomonitoring studies. As biomonitoring programs are refreshed, consideration of specific priority substances and specific population targets provide opportunities for inclusion of alternative non- or minimally invasive matrices. This review describes methods used in health risk assessment to characterize exposure and risk based upon biomarkers from noninvasive matrices other than urine or blood, including human milk, hair, fingernails, toenails, exhaled breath, deciduous teeth, sweat, semen, meconium, and feces. Illustrative examples of these methods relevant to chemical management are provided. This review suggests that, although these alternative noninvasive biomarkers are not frequently used in human health risk assessment at present, these biomarkers may prove useful in (1) characterizing exposure and health risk in vulnerable populations, (2) cumulative risk assessments, and (3) community-based risk assessments, depending upon the substance of concern. To incorporate alternative noninvasive biomarkers into human health risk assessments with confidence, more research is needed to improve our knowledge of the relationships between external dose, internal dose, and biologic consequent effects in matrices other than blood and urine. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to address the lack of spatial dose comparisons of planned and delivered rectal doses during prostate radiotherapy by using dose‐surface maps (DSMs) to analyze dose delivery accuracy and comparing these results to those derived using DVHs. Methods: Two independent cohorts were used in this study: twenty patients treated with 36.25 Gy in five fractions (SBRT) and 20 treated with 60 Gy in 20 fractions (IMRT). Daily delivered rectum doses for each patient were retrospectively calculated using daily CBCT images. For each cohort, planned and average‐delivered DVHs were generated and compared, as were planned and accumulated DSMs. Permutation testing was used to identify DVH metrics and DSM regions where significant dose differences occurred. Changes in rectal volume and position between planning and delivery were also evaluated to determine possible correlation to dosimetric changes. Results: For both cohorts, DVHs and DSMs reported conflicting findings on how planned and delivered rectum doses differed from each other. DVH analysis determined average‐delivered DVHs were on average 7.1% ± 7.6% (p ≤ 0.002) and 5.0 ± 7.4% (p ≤ 0.021) higher than planned for the IMRT and SBRT cohorts, respectively. Meanwhile, DSM analysis found average delivered posterior rectal wall dose was 3.8 ± 0.6 Gy (p = 0.014) lower than planned in the IMRT cohort and no significant dose differences in the SBRT cohort. Observed dose differences were moderately correlated with anterior‐posterior rectal wall motion, as well as PTV superior‐inferior motion in the IMRT cohort. Evidence of both these relationships were discernable in DSMs. Conclusion: DSMs enabled spatial investigations of planned and delivered doses can uncover associations with interfraction motion that are otherwise masked in DVHs. Investigations of dose delivery accuracy in radiotherapy may benefit from using DSMs over DVHs for certain organs such as the rectum. [ABSTRACT FROM AUTHOR]

The Rocky Flats (RF) Plant was a weapons manufacturing facility that operated from the early 1950s to 1989. Its primary missions were the production of plutonium (Pu) pits for thermonuclear weapons and the processing of retired weapons for Pu recovery. The purpose of this study was to estimate radiation doses to a cohort of 4499 RF workers from an intake of 239Pu, the primary plutonium isotope handled at the site. The latest biokinetic models of the International Commission on Radiological Protection, or site-specific variations of those models, were used to estimate 239Pu intakes for each worker based on model fits to bioassay data often coupled with lung measurements. Urinary excretion and lung retention data for most 239Pu intakes could be fit reasonably well by a mixture of Pu dioxide and moderately soluble material. For some workers, better fits were obtained by application of other absorption types including Type S, 239Pu nitrate, or pure 239Pu dioxide, or by assuming intake via a wound. The lungs typically received the highest tissue doses, with fifty-year committed equivalent doses in the range of 0.5–1 Sv for 275 workers, 1–5 Sv for 115 workers, and greater than 5 Sv for 12 workers. RF was a unique site regarding a large number of lung measurements available for determining the appropriate absorption types for inhaled material. This provided higher confidence in reconstructed 239Pu doses than is generally gained from urinary data alone. [ABSTRACT FROM AUTHOR]

At our institution, patients diagnosed with choroidal melanoma requiring external beam radiation therapy are treated with two 6 MV volumetric-modulated arcs delivering 50 Gy over 5 daily fractions. The patient is immobilized using an Orfit head and neck mask and is directed to look at a light emitting diode (LED) during CT simulation and treatment to minimize eye movement. Patient positioning is checked with cone beam computed tomography (CBCT) daily. Translational and rotational displacements greater than 1 mm or 1° off the planned isocenter position are corrected using a Hexapod couch. The aim of this study is to verify that the mask system provides adequate immobilization and to verify our 2-mm planning target volume (PTV) margins are sufficient. Residual displacements provided by pretreatment verification and post-treatment CBCT data sets were used to assess the impact of patient mobility during treatment on the reconstructed delivered dose to the target and organs at risk. The PTV margin calculated using van Herk's method1 was used to assess patient motion plus other factors that affect treatment position, such as kV-MV isocenter coincidence. Patient position variations were small and were shown to not cause significant dose variations between the planned and reconstructed dose to the target and organs at risk. The PTV margin analysis showed patient translational motion alone required a PTV margin of 1 mm. Given other factors that affect treatment delivery accuracy, a 2-mm PTV margin was shown to be sufficient for treatment of 95% of our patients with 100% of dose delivered to the GTV. The mask immobilization with LED focus is robust and we showed a 2-mm PTV margin is adequate with this technique. [ABSTRACT FROM AUTHOR]

Purpose: Transcriptomic-based approaches are being developed to meet the needs for large-scale radiation dose and injury assessment and provide population triage following a radiological or nuclear event. This review provides background and definition of the need for new biodosimetry approaches, and summarizes the major advances in this field. It discusses some of the major model systems used in gene signature development, and highlights some of the remaining challenges, including individual variation in gene expression, potential confounding factors, and accounting for the complexity of realistic exposure scenarios. Conclusions: Transcriptomic approaches show great promise for both dose reconstruction and for prediction of individual radiological injury. However, further work will be needed to ensure that gene expression signatures will be robust and appropriate for their intended use in radiological or nuclear emergencies. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to evaluate the intrafractional prostate motion captured during gated magnetic resonance imaging (MRI)-guided online adaptive radiotherapy for prostate cancer and analyze its impact on the delivered dose as well as the effect of gating. Methods: Sagittal 2D cine-MRI scans were acquired at 4 Hz during treatment at a ViewRay MRIdian (ViewRay Inc., Oakwood Village, OH, USA) MR linac. Prostate shifts in anterior–posterior (AP) and superior–inferior (SI) directions were extracted separately. Using the static dose cloud approximation, the planned fractional dose was shifted according to the 2D gated motion (residual motion in gating window) to estimate the delivered dose by superimposing and averaging the shifted dose volumes. The dose of a hypothetical non-gated delivery was reconstructed similarly using the non-gated motion. For the clinical target volume (CTV), rectum, and bladder, dose–volume histogram parameters of the planned and reconstructed doses were compared. Results: In total, 174 fractions (15.7 h of cine-MRI) from 10 patients were evaluated. The average (±1 σ) non-gated prostate motion was 0.6 ± 1.0 mm in the AP and 0.0 ± 0.6 mm in the SI direction with respect to the centroid position of the gating boundary. 95% of the shifts were within [−3.5, 2.7] mm in the AP and [−2.9, 3.2] mm in the SI direction. For the gated treatment and averaged over all fractions, CTV D98% decreased by less than 2% for all patients. The rectum and the bladder D2% increased by less than 3% and 0.5%, respectively. Doses reconstructed for gated and non-gated delivery were similar for most fractions. Conclusion: A pipeline for extraction of prostate motion during gated MRI-guided radiotherapy based on 2D cine-MRI was implemented. The 2D motion data enabled an approximate estimation of the delivered dose. For the majority of fractions, the benefit of gating was negligible, and clinical dosimetric constraints were met, indicating safety of the currently adopted gated MRI-guided treatment workflow. [ABSTRACT FROM AUTHOR]

Background: Pencil beam scanning (PBS) proton therapy can provide highly conformal target dose distributions and healthy tissue sparing. However, proton therapy of hepatocellular carcinoma (HCC) is prone to dosimetrical uncertainties induced by respiratory motion. This study aims to develop intra-treatment tumor motion monitoring during respiratory gated proton therapy and combine it with motion-including dose reconstruction to estimate the delivered tumor doses for individual HCC treatment fractions. Methods: Three HCC-patients were planned to receive 58 GyRBE (n=2) or 67.5 GyRBE (n=1) of exhale respiratory gated PBS proton therapy in 15 fractions. The treatment planning was based on the exhale phase of a 4-dimensional CT scan. Daily setup was based on cone-beam CT (CBCT) imaging of three implanted fiducial markers. An external marker block (RPM) on the patient’s abdomen was used for exhale gating in free breathing. This study was based on 5 fractions (patient 1), 1 fraction (patient 2) and 6 fractions (patient 3) where a post-treatment control CBCT was available. After treatment, segmented 2D marker positions in the post-treatment CBCT projections provided the estimated 3D motion trajectory during the CBCT by a probability-based method. An external-internal correlation model (ECM) that estimated the tumor motion from the RPM motion was built from the synchronized RPM signal and marker motion in the CBCT. The ECM was then used to estimate intra-treatment tumor motion. Finally, the motion-including CTV dose was estimated using a dose reconstruction method that emulates tumor motion in beam’s eye view as lateral spot shifts and in-depth motion as changes in the proton beam energy. The CTV homogeneity index (HI) The CTV homogeneity index (HI) was calculated as D2% − D98%/D50% ×100%. Results: The tumor position during spot delivery had a root-mean-square error of 1.3 mm in left-right, 2.8 mm in cranio-caudal and 1.7 mm in anterior-posterior directions compared to the planned position. On average, the CTV HI was larger than planned by 3.7%-points (range: 1.0-6.6%-points) for individual fractions and by 0.7%-points (range: 0.3-1.1%-points) for the average dose of 5 or 6 fractions. Conclusions: A method to estimate internal tumor motion and reconstruct the motion-including fraction dose for PBS proton therapy of HCC was developed and demonstrated successfully clinically. [ABSTRACT FROM AUTHOR]

Background: It has been well-established that acute radiation exposures increase the risk of leukemia. However, it is still unknown whether these leukemia risk estimates could be extrapolated to occupational populations who receive repeated low-dose radiation exposure. The purpose of this study was to estimate quantified associations between low-dose radiation exposures and leukemia. Methods: The Chinese medical X-ray worker study (CMXW) included 27,011 medical X-ray workers employed at major hospitals in 24 provinces in China from 1950 to 1980, and a control population of 25,782 physicians matched by hospital, who were unexposed to X-ray equipment. Poisson regression models were used to estimate the excess relative risk (ERR) and excess absolute risk (EAR) for the incidence of leukemia associated with cumulative doses. A meta-analysis of the published literature on low-dose occupational radiation exposure and leukemia risk was also conducted. Results: The incidence rates of leukemia in X-ray workers and the control group were 6.70 and 3.39 per 100,000 person-years, respectively. Among X-ray workers, the average cumulative red bone marrow dose was 0.046 Gy. We found a positive relationship between 2-year lagged cumulative red bone marrow dose and risk of leukemia excluding chronic lymphocytic leukemia (CLL) (ERR = 0.66 per 100 mGy, 90% CI: 0.091.53; EAR = 0.29 per 104 PY-100 mGy, 90% CI: 0.070.56). The excess risk was largely driven by myeloid leukemia (ERR = 1.06 per 100 mGy, 90% CI: 0.22, 2.51). Based on the meta-analysis, the pooled ERR at 100 mGy was 0.19 (95% CI: 0.080.31). Conclusion: This study provides strong evidence of a positive and linear doseresponse relationship between cumulative red bone marrow dose and the incidence of non-CLL leukemia.

To estimate the physical dose of skin and key organs in a case of overexposure during a cardiac interventional procedure. Methods: The female patient aged 50 suffered from overexposure during cardiac interventional therapy in a hospital, Xinxiang city, Henan province, China in January 2020. The mesh-type phantom for the patient was constructed based on the adult mesh-type reference computational phantoms (MRCPs) released by the International Commission on Radiological Protection Publication 145 (ICRP145) and phantom deformation technology. Models of exposure scenario were constructed and simulated with particle and heavy ion transport code system (PHITS) according to exposure conditions. Results: The maximum absorbed dose of key organs/tissues under irradiation in posteroanterior (PA) and 30° left anterior oblique directions(LOA) was 632.4 and 305.6 ​mGy, respectively. The left lung, heart, and left mammary gland received a larger dose under both irradiation conditions. The ratio of the absorbed dose with and without shielding was calculated, and the relative difference in most organs was

BackgroundPencil beam scanning (PBS) proton therapy can provide highly conformal target dose distributions and healthy tissue sparing. However, proton therapy of hepatocellular carcinoma (HCC) is prone to dosimetrical uncertainties induced by respiratory motion. This study aims to develop intra-treatment tumor motion monitoring during respiratory gated proton therapy and combine it with motion-including dose reconstruction to estimate the delivered tumor doses for individual HCC treatment fractions.MethodsThree HCC-patients were planned to receive 58 GyRBE (n=2) or 67.5 GyRBE (n=1) of exhale respiratory gated PBS proton therapy in 15 fractions. The treatment planning was based on the exhale phase of a 4-dimensional CT scan. Daily setup was based on cone-beam CT (CBCT) imaging of three implanted fiducial markers. An external marker block (RPM) on the patient’s abdomen was used for exhale gating in free breathing. This study was based on 5 fractions (patient 1), 1 fraction (patient 2) and 6 fractions (patient 3) where a post-treatment control CBCT was available. After treatment, segmented 2D marker positions in the post-treatment CBCT projections provided the estimated 3D motion trajectory during the CBCT by a probability-based method. An external-internal correlation model (ECM) that estimated the tumor motion from the RPM motion was built from the synchronized RPM signal and marker motion in the CBCT. The ECM was then used to estimate intra-treatment tumor motion. Finally, the motion-including CTV dose was estimated using a dose reconstruction method that emulates tumor motion in beam’s eye view as lateral spot shifts and in-depth motion as changes in the proton beam energy. The CTV homogeneity index (HI) The CTV homogeneity index (HI) was calculated as D2% − D98%D50% ×100%.ResultsThe tumor position during spot delivery had a root-mean-square error of 1.3 mm in left-right, 2.8 mm in cranio-caudal and 1.7 mm in anterior-posterior directions compared to the planned position. On average, the CTV HI was larger than planned by 3.7%-points (range: 1.0-6.6%-points) for individual fractions and by 0.7%-points (range: 0.3-1.1%-points) for the average dose of 5 or 6 fractions.ConclusionsA method to estimate internal tumor motion and reconstruct the motion-including fraction dose for PBS proton therapy of HCC was developed and demonstrated successfully clinically.

• Developed a colorectal model that includes anatomical variations of 103 individuals. • Colorectal model is age-scalable (0.1–18 years) across the pediatric age range. • Integrated colorectal model into the age-scalable in-house phantom. • The colorectal model can be integrated into any computational phantom. • The colorectal model will be used for dose reconstruction in late effects studies. The purposes of this study were to develop and integrate a colorectal model that incorporates anatomical variations of pediatric patients into the age-scalable MD Anderson Late Effects (MDA-LE) computational phantom, and validate the model for pediatric radiation therapy (RT) dose reconstructions. Colorectal contours were manually derived from whole-body non-contrast computed tomography (CT) scans of 114 pediatric patients (age range: 2.1–21.6 years, 74 males, 40 females). One contour was used for an anatomical template, 103 for training and 10 for testing. Training contours were used to create a colorectal principal component analysis (PCA)-based statistical shape model (SSM) to extract the population's dominant deformations. The SSM was integrated into the MDA-LE phantom. Geometric accuracy was assessed between patient-specific and SSM contours using several overlap metrics. Two alternative colorectal shapes were generated using the first 17 dominant modes of the PCA-based SSM. Dosimetric accuracy was assessed by comparing colorectal doses from test patients' CT-based RT plans (ground truth) with reconstructed doses for the mean and two alternative models in age-matched MDA-LE phantoms. When using all 103 PCA modes, the mean (min–max) Dice similarity coefficient, distance-to-agreement and Hausdorff distance between the patient-specific and reconstructed contours for the test patients were 0.89 (0.85–0.91), 2.1 mm (1.7–3.0), and 8.6 mm (5.7–14.3), respectively. The average percent difference between reconstructed and ground truth mean and maximum colorectal doses for the mean (alternative 1, 2) model were 6.3% (8.1%, 6.1%) and 4.4% (4.3%, 4.7%), respectively. We developed, validated and integrated a colorectal PCA-based SSM into the MDA-LE phantom and demonstrated its dosimetric performance for accurate pediatric RT dose reconstruction. [ABSTRACT FROM AUTHOR]

Objective . The primary purpose of this work is to demonstrate the feasibility of a deep convolutional neural network (dCNN) based algorithm that uses two-dimensional (2D) electronic portal imaging device (EPID) images and CT images as input to reconstruct 3D dose distributions inside the patient. Approach . To generalize dCNN training and testing data, geometric and materials models of a VitalBeam accelerator treatment head and a corresponding EPID imager were constructed in detail in the GPU-accelerated Monte Carlo dose computing software, ARCHER. The EPID imager pixel spatial resolution ranging from 1.0 mm to 8.5 mm was studied to select optimal pixel size for simulation. For purposes of training the U-Net-based dCNN, a total of 101 clinical intensive modulated radiation treatment cases-81 for training, 10 for validation, and 10 for testing-were simulated to produce comparative data of 3D dose distribution versus 2D EPID image data. The model's accuracy was evaluated by comparing its predictions with Monte Carlo dose. Main Results . Using the optimal EPID pixel size of 1.5 mm, it took about 18 min to simulate the particle transport in patient-specific CT and EPID imager per a single field. In contrast, the trained dCNN can predict 3D dose distributions in about 0.35 s. The average 3D gamma passing rates between ARCHER and predicted doses are 99.02 ± 0.57% (3%/3 mm) and 96.85 ± 1.22% (2%/2 mm) for accumulated fields, respectively. Dose volume histogram data suggest that the proposed dCNN 3D dose prediction algorithm is accurate in evaluating treatment goals. Significance . This study has proposed a novel deep-learning model that is accurate and rapid in predicting 3D patient dose from 2D EPID images. The computational speed is expected to facilitate clinical practice for EPID-based in-vivo patient-specific quality assurance towards adaptive radiation therapy., (© 2025 Institute of Physics and Engineering in Medicine. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

• Evaluation of MR-guided beam gating based on patient data. • Estimation of residual motion during gating and its dosimetric effect. • Dose reconstruction workflow for individual patient motion. This study aims to investigate the efficiency and the geometric as well as the dosimetric benefit of magnetic-resonance guided beam gating for stereotactic treatments in moving organs. Patients treated with MR-guided (MRIdian system) SBRT for lung (n = 10) and liver (n = 10) targets were analyzed. Breath-hold gating was performed based on lesion tracking in sagittal cine MRI images. The target offset from the geometric center of the gating window with and without gating was evaluated. A dose reconstruction workflow based on convolution of these 2D position-probability maps and the daily 3D dose distribution was used to estimate the daily delivered dose including motion. The dose to the clinical target volume (CTV) and to a 2-cm ring structure around the planning target volume were evaluated. The applied gating protocol resulted in a mean (±standard deviation) gating efficiency of 55%±16%. Over all patients, the mean target offset (2D-root-mean-square error) was 8.3 ± 4.3 mm, which reduced to 2.4 ± 0.6 mm during gating. The dose reconstruction showed a mean deviation in CTV coverage (D95) from the static plans of −1.7%±1.8% with gating and −12.0%±8.4% if no gating would have been used. The mean dose (Dmean) in the ring structure, with respect to the static plans, showed mean deviations of −0.1%±0.3% with gating and −1.6%±1.8% without gating. The MRIdian system enables gating based on the inner anatomy and the implemented dose reconstruction workflow demonstrated geometric robust delivery of the planned radiation doses. [ABSTRACT FROM AUTHOR]

Objective. A retrospective study on secondary cancer risk on carbon ion radiotherapy (CIRT) is ongoing at the Heavy Ion Medical Accelerator in Chiba (HIMAC). The reconstruction of the whole-body patient dose distribution is the key issue in the study because dose distribution only around the planning target volume was evaluated in the treatment planning system. Approach. We therefore developed a new dose reconstruction system based on the Particle and Heavy Ion Transport code System (PHITS) coupled with the treatment plan DICOM data set by extending the functionalities of RadioTherapy package based on PHITS (RT-PHITS). In the system, the geometry of patient-specific beam devices such as the range shifter, range compensator, and collimators as well as the individual patient’s body are automatically reconstructed. Various functions useful for retrospective analysis on the CIRT are implemented in the system, such as those for separately deducing dose contributions from different secondary particles and their origins. Main results. The accuracy of the developed system was validated by comparing the dose distribution to the experimental data measured in a water tank and using a treatment plan on an anthropomorphic phantom. Significance. The extended RT-PHITS will be used in epidemiological studies based on clinical data from HIMAC. [ABSTRACT FROM AUTHOR]

As part of the Million Person Study (MPS), dose reconstructions for internal emitters have been performed for several U.S. facilities where large quantities of radionuclides were handled. The main challenges and dominant sources of potential error in retrospective dose estimates for internally exposed workers have been found to vary from site to site. This article discusses some important issues encountered in dose reconstructions performed for selected MPS sites and the approaches used to address those issues. The focus is on some foundational components of retrospective dose assessments that have received little attention in the literature. The discussion is built around illustrative exposure data and dose reconstructions for workers at selected facilities addressed in the MPS. Related findings at some non-MPS sites are also discussed. Each of the following items has been found to be a major source of potential error in reconstructed tissue doses for some MPS sites: identification of all dosimetrically important internal emitters; the time pattern of intake; the mode(s) of intake; reliability of bioassay measurements; application of surrogate (coworker) information in lieu of, or in conjunction with, worker-specific monitoring data; the chemical and physical forms of inhaled radionuclides; and the relation of air monitoring data to actual intake. (1) Much of the dose reconstruction effort for internal emitters should be devoted to development of best feasible exposure scenarios. (2) Coworker data should be used to assign exposure scenarios or dose estimates to workers with missing exposure data only if there is compelling evidence of similar coworker exposure. (3) Bioassay data for some radionuclides and periods of operation at MPS sites are of questionable reliability due to sizable uncertainties associated with contamination, recovery, or background issues. (4) Dose estimates derived solely from air monitoring data should be treated as highly uncertain values in the absence of site-specific information demonstrating that the data are reasonably predictive of intake. (5) For intakes known or assumed to be via inhalation, the uncertainty in lung dose typically is much greater than the uncertainty in dose to systemic tissues, when dose estimates are based on urinary excretion data. (6) The lung dose estimate often can be improved through development of site-specific respiratory absorption parameter values. (7) There is generally insufficient site-specific information to justify development of site-specific systemic models. [ABSTRACT FROM AUTHOR]

Abstract There is no ideal detector-phantom combination to perform patient specific quality assurance (PSQA) for Total Marrow (TMI) and Lymphoid (TMLI) Irradiation plan. In this study, 3D dose reconstruction using mega voltage computed tomography detectors measured Leaf Open Time Sinogram (LOTS) was investigated for PSQA of TMI/TMLI patients in helical tomotherapy. The feasibility of this method was first validated for ten non-TMI/TMLI patients, by comparing reconstructed dose with (a) ion-chamber (IC) and helical detector array (ArcCheck) measurement and (b) planned dose distribution using 3Dγ analysis for 3%@3mm and dose to 98% (D98%) and 2% (D2%) of PTVs. Same comparison was extended for ten treatment plans from five TMI/TMLI patients. In all non-TMI/TMLI patients, reconstructed absolute dose was within ± 1.80% of planned and IC measurement. The planned dose distribution agreed with reconstructed and ArcCheck measured dose with mean (SD) 3Dγ of 98.70% (1.57%) and 2Dγ of 99.48% (0.81%). The deviation in D98% and D2% were within 1.71% and 4.10% respectively. In all 25 measurement locations from TMI/TMLI patients, planned and IC measured absolute dose agreed within ± 1.20%. Although sectorial fluence verification using ArcCHECK measurement for PTVs chest from the five upper body TMI/TMLI plans showed mean ± SD 2Dγ of 97.82% ± 1.27%, the reconstruction method resulted poor mean (SD) 3Dγ of 92.00% (± 5.83%), 64.80% (± 28.28%), 69.20% (± 30.46%), 60.80% (± 19.37%) and 73.2% (± 20.36%) for PTVs brain, chest, torso, limb and upper body respectively. The corresponding deviation in median D98% and D2% of all PTVs were

Purpose: Gamma Knife Icon (GKI) enables a user‐defined gating threshold for intrafraction motion during stereotactic radiosurgery (SRS). An optimal threshold would ensure dosimetric fidelity of the planned distribution and minimize treatment time extension by gating. A prediction of motion characteristics for a patient based on a retrospective database of motion traces could be beneficial to evaluating the choice of gating threshold. A short acquisition of motion may help to define a personalized threshold that balances dosimetric accuracy and treatment length. This study aims to evaluate the performance of a prediction of motion and the resultant dosimetric consequences for a range of motion gating thresholds. Methods: A database of 2552 motion traces (776 patients) was analyzed using previously published methods to characterize patient intrafraction motion on the GKI. For a selection of six fractionated SRS patient cases (two patients with single brain metastasis, four vestibular schwannomas), a 10‐min sample of motion was used to classify motion and identify traces in the database with similar metrics. The similar motion traces were used to perform a predictive reconstruction of the selected patient's delivered dose for a range of motion thresholds. The remaining fractions were reconstructed and compared to that predicted. From the six cases, 26 fractions were used to predict the number of interruptions (n = 26), change in target coverage (n = 26), and change in brainstem maximum dose (vestibular cases only, n = 20). The difference between mean predicted and reconstructed values was compared for accuracy. Results: The difference between mean prediction and reconstructed values was 0.32 ± 0.38% in target coverage, 2.36 ± 5.06 interruptions, and 0.15 ± 0.24 Gy for the brainstem maximum dose. Sixty‐seven of the 72 predictions (26 coverage, 26 interruptions, and 20 brainstem maximum dose) were within one standard deviation of the predicted mean. Conclusions: Large databases of motion traces were used to characterize patient performance and predict motion performance. Dosimetric deterioration due to motion and extension of treatment duration can be predicted in some cases using only a short acquisition of motion and the treatment plan. This reconstruction may provide benefit in generating a patient‐specific motion threshold. [ABSTRACT FROM AUTHOR]

Abstract Objectives To derive conversions of antiquated exposure data into modern equivalents and to apply these in the assessment of the skin dose of pelvic radiographs since 1896. Methods The literature 1896–2018 was searched for implicit and explicit dose information. The early implicit dose data contained now obsolete descriptions of radiation quality and quantity for long since disappeared X-ray systems of limited efficiency. Converting the old information into modern specifications was achieved using contemporary data and computer simulations. Final dose calculations were done with modern software. Explicit radiation doses of later date reported in old quantities and units were adapted according to current recommendations. Results For the period before 1927 conversion algorithms for spark gap data and penetrometer hardnesses to high voltage could be derived. Electrical and X-ray efficiencies of several old röntgen systems were determined. Together they allowed reconstruction of 53 doses. After 1927 doses were generally explicitly specified; 114 were retrieved. Although an enormous spread was observed, the average skin dose was reduced by a factor of about 400. Conclusions Antiquated exposure data were successfully used for dose reconstruction. Extreme dose variability was a constant. Efforts to cut down doses were effective as skin doses went down from sub-erythema values to about one milligray.

• 15 prostate cancer patients were treated with a single SBRT fraction of 19 Gy. • Intrafraction motion was tracked with intraprostatic electromagnetic transponders. • Intrafraction target motion was simulated in the original treatment plans. • Intrafraction motion did not impair target coverage or treatment safety. • Protocol violations were minimal despite prostate motion. To reconstruct the dose delivered during single-fraction urethra-sparing prostate stereotactic body radiotherapy (SBRT) accounting for intrafraction motion monitored by intraprostatic electromagnetic transponders (EMT). We analyzed data of 15 patients included in the phase I/II "ONE SHOT" trial and treated with a single fraction of 19 Gy to the planning target volume (PTV) and 17 Gy to the urethra planning risk volume. During delivery, prostate motion was tracked with implanted EMT. SBRT was interrupted when a 3-mm threshold was trespassed and corrected unless the offset was transient. Motion-encoded reconstructed (MER) plans were obtained by splitting the original plans into multiple sub-beams with isocenter shifts based on recorded EMT positions, mimicking prostate motion during treatment. We analyzed intrafraction motion and compared MER to planned doses. The median EMT motion range (±SD) during delivery was 0.26 ± 0.09, 0.22 ± 0.14 and 0.18 ± 0.10 cm in the antero-posterior, supero-inferior, and left–right axes, respectively. Treatment interruptions were needed for 8 patients because of target motion beyond limits in the antero-posterior (n = 6) and/or supero-inferior directions (n = 4). Comparing MER vs. original plan there was a median relative dose difference of −1.9% (range, −7.9 to −1.0%) and of +0.5% (−0.3–1.7%) for PTV D 98% and D 2% , respectively. The clinical target volume remained sufficiently covered with a median D 98% difference of −0.3% (−1.6–0.5%). Bladder and rectum dosimetric parameters showed significant differences between original and MER plans, but mostly remained within acceptable limits. The dosimetric impact of intrafraction prostate motion was minimal for target coverage for single-fraction prostate SBRT with real-time electromagnetic tracking combined with beam gating. [ABSTRACT FROM AUTHOR]

Biokinetic models have been employed in internal dosimetry (ID) to model the human body's time-dependent retention and excretion of radionuclides. Consequently, biokinetic models have become instrumental in modelling the body burden from biological processes from internalized radionuclides for prospective and retrospective dose assessment. Solutions to biokinetic equations have been modelled as a system of coupled ordinary differential equations (ODEs) representing the time-dependent distribution of materials deposited within the body. In parallel, several mathematical algorithms were developed for solving general kinetic problems, upon which biokinetic solution tools were constructed. This paper provides a comprehensive review of mathematical solving methods adopted by some known internal dose computer codes for modelling the distribution and dosimetry for internal emitters, highlighting the mathematical frameworks, capabilities, and limitations. Further discussion details the mathematical underpinnings of biokinetic solutions in a unique approach paralleling advancements in ID. The capabilities of available mathematical solvers in computational systems were also emphasized. A survey of ODE forms, methods, and solvers was conducted to highlight capabilities for advancing the utilization of modern toolkits in ID. This review is the first of its kind in framing the development of biokinetic solving methods as the juxtaposition of mathematical solving schemes and computational capabilities, highlighting the evolution in biokinetic solving for radiation dose assessment., (© 2024 Society for Radiological Protection. Published on behalf of SRP by IOP Publishing Limited. All rights reserved.)

Background and purpose: To evaluate the feasibility of dose-guided adaptive radiotherapy (ART) based on deformable image registration (DIR) using fractional megavoltage cone-beam CT (MVCBCT) images from Halcyon system that uses identical beams for treatment and imaging and to retrospectively investigate the influence of anatomic changes on target coverage and organ-at-risk (OAR) sparing across various tumor sites.Materials and Methods: Four hundred twenty-two MVCBCT images from 16 patients (three head and neck, seven thoracic, three abdominal, and three pelvic cases) treated in a phase II clinical trial for Halcyon were selected. DIR between the planning CT and daily MVCBCT image was implemented by Velocity software to create pseudo CT. To investigate the accuracy of dose calculation on pseudo CT, three evaluation patients with rescanned CT and adaptive plans were selected. Dose distribution of adaptive plans calculated on pseudo CT was compared with that calculated on the rescanned planning CT on the three evaluation patients. To investigate the impact of inter-fractional anatomic changes on target dose coverage and dose to OARs of the 16 patients, fractional dose was calculated and accumulated incrementally based on deformable registration between planning CT and daily MVCBCT images.Results: Passing rates using 3 mm/3%/10% threshold local gamma analysis were 93.04, 96.00, and 91.68%, respectively, for the three evaluation patients between the reconstructed dose on pseudo CT (MVCBCT) and rescanned CT, where accumulated dose deviations of over 97% voxels were smaller than 0.5 Gy. Planning target volume (PTV) D95% and D90% (the minimum dose received by at least 95/90% of the volume) of the accumulated dose could be as low as 93.8 and 94.5% of the planned dose, respectively. OAR overdose of various degrees were observed in the 16 patients relative to the planned dose. In most cases, OARs' dose volume histogram (DVH) lines of accumulated and planned dose were very close to each other if not overlapping. Among cases with visible deviations, the differences were bilateral without apparent patterns specific to tumor sites or organs.Conclusion: As a confidence building measure, this simulation study suggested the possibility of ART for Halcyon based on DIR between planning CT and MVCBCT. Preliminary clinical data suggested the benefit of patient-specific dose reconstruction and ART to avoid unacceptable target underdosage and OAR overdosage.

Abstract Background Conventional phantom-based planar dosimetry (2D-PBD) quality assurance (QA) using gamma pass rate (GP (%)) is inadequate to reflect clinically relevant dose error in intensity-modulated radiation therapy (IMRT), owing to a lack of information regarding patient anatomy and volumetric dose distribution. This study aimed to evaluate the dose distribution accuracy of IMRT delivery for nasopharyngeal carcinoma (NPC), which passed the 2D-PBD verification, using a measurement-guided 3D dose reconstruction (3D-MGR) method. Methods Radiation treatment plans of 30 NPC cases and their pre-treatment 2D-PBD data were analyzed. 3D dose distribution was reconstructed on patient computed tomography (CT) images using the 3DVH software and compared to the treatment plans. Global and organ-specific dose GP (%), and dose-volume histogram (DVH) deviation of each structure was evaluated. Interdependency between GP (%) and the deviation of the volumetric dose was studied through correlation analysis. Results The 3D-MGR achieved global GP (%) similar to conventional 2D-PBD in the same criteria. However, structure-specific GP (%) significantly decreased under stricter criteria, including the planning target volume (PTV). The average deviation of all inspected dose volumes (DV) and volumetric dose (VD) parameters ranged from − 2.93% to 1.17%, with the largest negative deviation in V100% of the PTVnx of − 15.66% and positive deviation in D1cc of the spinal cord of 6.66%. There was no significant correlation between global GP (%) of 2D-PBD or 3D-MGR and the deviation of the most volumetric dosimetry parameters (DV or VD), when the Pearson’s coefficient value of 0.8 was used for correlation evaluation. Conclusion Even upon passing the pre-treatment phantom based dosimetric QA, there could still be risk of dose error like under-dose in PTVnx and overdose in critical structures. Measurement-guided 3D volumetric dosimetry QA is recommended as the more clinically efficient verification for the complicated NPC IMRT.

Abstract Background Volumetric-modulated Dynamic WaveArc therapy (VMDWAT) is a non-coplanar continuous volumetric modulated radiation therapy (VMAT) delivery technique. Here, we monitored mechanical errors and their impact on dose distributions in VMDWAT using logfiles throughout the course of treatment. Methods Fifteen patients were enrolled (2 skull base tumor patients and 13 prostate cancer patients). VMDWAT plans were created for the enrolled patients. The prescribed dose for the skull base tumor was set as 54 Gy at 1.8 Gy per fraction, and that for the prostate cancer was set as 72 to 78 Gy at 2 Gy per fraction. We acquired logfiles to monitor mechanical errors and their impact on dose distribution in each fraction. The root mean square error (RMSE) in the multi-leaf collimator (MLC), gantry angle, O-ring angle and monitor unit (MU) were calculated using logfiles throughout the course of VMDWAT for each patient. The dosimetric impact of mechanical errors throughout the course of VMDWAT was verified using a logfile-based dose reconstruction method. Dosimetric errors between the reconstructed plans and the original plans were assessed. Results A total of 517 datasets, including 55 datasets for the 2 skull base tumor patients and 462 datasets for the 13 prostate cancer patients, were acquired. The RMSE values were less than 0.1 mm, 0.2°, 0.1°, and 0.4 MU for MLC position, gantry angle, O-ring angle, and MU, respectively. For the skull base tumors, the absolute mean dosimetric errors and two standard deviations throughout the course of treatment were less than 1.4% and 1.1%, respectively. For prostate cancer, these absolute values were less than 0.3% and 0.5%, respectively. The largest dosimetric error of 2.5% was observed in a skull base tumor patient. The resultant dosimetric error in the accumulated daily delivered dose distribution, in the patient with the largest error, was up to 1.6% for all dose-volumetric parameters relative to the planned dose distribution. Conclusions MLC position, gantry rotation, O-ring rotation and MU were highly accurate and stable throughout the course of treatment. The daily dosimetric errors due to mechanical errors were small. VMDWAT provided high delivery accuracy and stability throughout the course of treatment. Trial registration UMIN000023870. Registered: 1 October 2016.

There is no ideal detector-phantom combination to perform patient specific quality assurance (PSQA) for Total Marrow (TMI) and Lymphoid (TMLI) Irradiation plan. In this study, 3D dose reconstruction using mega voltage computed tomography detectors measured Leaf Open Time Sinogram (LOTS) was investigated for PSQA of TMI/TMLI patients in helical tomotherapy. The feasibility of this method was first validated for ten non-TMI/TMLI patients, by comparing reconstructed dose with (a) ion-chamber (IC) and helical detector array (ArcCheck) measurement and (b) planned dose distribution using 3Dγ analysis for 3%@3mm and dose to 98% (D98%) and 2% (D2%) of PTVs. Same comparison was extended for ten treatment plans from five TMI/TMLI patients. In all non-TMI/TMLI patients, reconstructed absolute dose was within ± 1.80% of planned and IC measurement. The planned dose distribution agreed with reconstructed and ArcCheck measured dose with mean (SD) 3Dγ of 98.70% (1.57%) and 2Dγ of 99.48% (0.81%). The deviation in D98% and D2% were within 1.71% and 4.10% respectively. In all 25 measurement locations from TMI/TMLI patients, planned and IC measured absolute dose agreed within ± 1.20%. Although sectorial fluence verification using ArcCHECK measurement for PTVs chest from the five upper body TMI/TMLI plans showed mean ± SD 2Dγ of 97.82% ± 1.27%, the reconstruction method resulted poor mean (SD) 3Dγ of 92.00% (± 5.83%), 64.80% (± 28.28%), 69.20% (± 30.46%), 60.80% (± 19.37%) and 73.2% (± 20.36%) for PTVs brain, chest, torso, limb and upper body respectively. The corresponding deviation in median D98% and D2% of all PTVs were < 3.80% and 9.50%. Re-optimization of all upper body TMI/TMLI plans with new pitch and modulation factor of 0.3 and 3 leads significant improvement with 3Dγ of 100% for all PTVs and median D98% and D2% < 1.6%. LOTS based PSQA for TMI/TMLI is accurate, robust and efficient. A field width, pitch and modulation factor of 5 cm, 0.3 and 3 for upper body TMI/TMLI plan is suggested for better dosimetric outcome and PSQA results. [ABSTRACT FROM AUTHOR]

Background and purpose: To evaluate the feasibility of dose-guided adaptive radiotherapy (ART) based on deformable image registration (DIR) using fractional megavoltage cone-beam CT (MVCBCT) images from Halcyon system that uses identical beams for treatment and imaging and to retrospectively investigate the influence of anatomic changes on target coverage and organ-at-risk (OAR) sparing across various tumor sites. Materials and Methods: Four hundred twenty-two MVCBCT images from 16 patients (three head and neck, seven thoracic, three abdominal, and three pelvic cases) treated in a phase II clinical trial for Halcyon were selected. DIR between the planning CT and daily MVCBCT image was implemented by Velocity software to create pseudo CT. To investigate the accuracy of dose calculation on pseudo CT, three evaluation patients with rescanned CT and adaptive plans were selected. Dose distribution of adaptive plans calculated on pseudo CT was compared with that calculated on the rescanned planning CT on the three evaluation patients. To investigate the impact of inter-fractional anatomic changes on target dose coverage and dose to OARs of the 16 patients, fractional dose was calculated and accumulated incrementally based on deformable registration between planning CT and daily MVCBCT images. Results: Passing rates using 3 mm/3%/10% threshold local gamma analysis were 93.04, 96.00, and 91.68%, respectively, for the three evaluation patients between the reconstructed dose on pseudo CT (MVCBCT) and rescanned CT, where accumulated dose deviations of over 97% voxels were smaller than 0.5 Gy. Planning target volume (PTV) D95% and D90% (the minimum dose received by at least 95/90% of the volume) of the accumulated dose could be as low as 93.8 and 94.5% of the planned dose, respectively. OAR overdose of various degrees were observed in the 16 patients relative to the planned dose. In most cases, OARs' dose volume histogram (DVH) lines of accumulated and planned dose were very close to each other if not overlapping. Among cases with visible deviations, the differences were bilateral without apparent patterns specific to tumor sites or organs. Conclusion: As a confidence building measure, this simulation study suggested the possibility of ART for Halcyon based on DIR between planning CT and MVCBCT. Preliminary clinical data suggested the benefit of patient-specific dose reconstruction and ART to avoid unacceptable target underdosage and OAR overdosage. [ABSTRACT FROM AUTHOR]

This study aimed to reconstruct the dose distribution of single fraction of stereotactic body radiotherapy for patients with prostate cancer using cone-beam computed tomography (CBCT) and a log file during volumetric-modulated arc therapy (VMAT) delivery with flattening-filter-free (FFF) mode. Twenty patients with clinically localized prostate cancer were treated with FFF-VMAT, and projection images for in-treatment CBCT (iCBCT) imaging were concomitantly acquired with a log file. A D95 dose of 36.25 Gy in five fractions was prescribed to each planning target volume (PTV) on each treatment planning CT (pCT). Deformed pCT (dCT) was obtained from the iCBCT using a hybrid deformable image registration algorithm. Dose distributions on the dCT were calculated using Pinnacle3 v9.10 by converting the log file data to Pinnacle3 data format using an in-house software. Dose warping was performed by referring to deformation vector fields calculated from pCT and dCT. Reconstructed dose distribution was compared with that of the original plan. Dose differences between the original and reconstructed dose distributions were within 3% at the isocenter and observed in PTV and organ-at-risk (OAR) regions. Differences in OAR regions were relatively larger than those in the PTV, presumably because OARs were more deformed than the PTV. Therefore, our method can be used successfully to reconstruct the dose distributions of one fraction using iCBCT and a log file during FFF-VMAT delivery. [ABSTRACT FROM AUTHOR]

• CBCT-guided pre-treatment localization strategy may lead to inaccurate treatment delivery. • Additional pre-treatment position correction increases the accuracy of treatment delivery. • Continuous motion monitoring ensures correct target coverage and minimizes OAR doses for every fraction. The aim of this study was to evaluate the dosimetric effect of continuous motion monitoring based localization (Calypso, Varian Medical Systems), gating and intrafraction motion correction in prostate SBRT. Delivered doses were modelled by reconstructing motion inclusive dose distributions for different localization strategies. Actually delivered dose (strategy A) utilized initial Calypso localization, CBCT and additional pre-treatment motion correction by kV-imaging and Calypso, and gating during the irradiation. The effect of gating was investigated by simulating non-gated treatments (strategy B). Additionally, non-gated and single image-guided (CBCT) localization was simulated (strategy C). A total of 308 fractions from 22 patients were reconstructed. The dosimetric effect was evaluated by comparing motion inclusive target and risk organ dose-volume parameters to planned values. Motion induced dose deficits were seen mainly in PTV and CTV to PTV margin regions, whereas CTV dose deficits were small in all strategies: mean ± SD difference in CTVD99% was –0.3 ± 0.4%, −0.4 ± 0.6% and –0.7 ± 1.2% in strategies A, B and C, respectively. Largest dose deficits were seen in individual fractions for strategy C (maximum dose reductions were −29.0% and –7.1% for PTVD95% and CTVD99%, respectively). The benefit of gating was minor, if additional motion correction was applied immediately prior to irradiation. Continuous motion monitoring based localization and motion correction ensured the target coverage and minimized the OAR exposure for every fraction and is recommended to use in prostate SBRT. The study is part of clinical trial NCT02319239. [ABSTRACT FROM AUTHOR]

• Novel dose reconstruction workflow based on log files and online MR imaging. • Intrafractional motion and dose changes were clinically meaningless in most fractions. • Rarely, large shifts caused the delivered dose to deviate from the treatment plan. • Blueprint for dose reconstruction on MR-linacs for other cancer sites. Anatomical changes during external beam radiotherapy prevent the accurate delivery of the intended dose distribution. Resolving the delivered dose, which is currently unknown, is crucial to link radiotherapy doses to clinical outcomes and ultimately improve the standard of care. In this study, we present a dose reconstruction workflow based on data routinely acquired during MR-guided radiotherapy. It employs 3D MR images, 2D cine MR images and treatment machine log files to calculate the delivered dose taking intrafractional motion into account. The developed pipeline was used to measure anatomical changes and assess their dosimetric impact in 89 prostate radiotherapy fractions delivered with a 1.5 T MR-linac at our institute. Over the course of radiation delivery, the CTV shifted 0.6 mm ± 2.1 mm posteriorly and 1.3 mm ± 1.5 mm inferiorly. When extrapolating the dose changes in each case to 20 fractions, the mean clinical target volume D 98 % and clinical target volume D 50 % dose-volume metrics decreased by 1.1 Gy ± 1.6 Gy and 0.1 Gy ± 0.2 Gy, respectively. Bladder D 3 % did not change (0.0 Gy ± 1.2 Gy), while rectum D 3 % decreased by 1.0 Gy ± 2.0 Gy. Although anatomical changes and their dosimetric impact were small in the majority of cases, large intrafractional motion caused the delivered dose to substantially deviate from the intended plan in some fractions. The presented end-to-end workflow is able to reliably, non-invasively and automatically reconstruct the delivered prostate radiotherapy dose by processing MR-linac treatment log files and online MR images. In the future, we envision this workflow to be adapted to other cancer sites and ultimately to enter widespread clinical use. [ABSTRACT FROM AUTHOR]

• This study investigates the accuracy of DIR based dose accumulation. • This study used an in silico ground truth based on clinically observed deformations. • The dose accumulation uncertainty was determined for individual structure types. • Uncertainties were separately determined for inverse (in)consistent voxels. • These results can be prospectively used to assess dose reconstruction accuracy. Deformable image registration (DIR) facilitated dose reconstruction and accumulation can be applied to assess delivered dose and verify the validity of the treatment plan during treatment. This retrospective study used in silico deformations based on clinically observed anatomical changes as ground truth to investigate the uncertainty of reconstructed and accumulated dose in head-and-neck radiotherapy (HNRT). A planning CT (pCT), cone beam CT (CBCT) from week one of treatment and three later CBCTs were selected for 12 HNRT patients. These images were used to generate in silico reference CBCTs and deformation vector fields (DVFs) as ground truth with B-spline DIR. Inverse consistency (IC) of voxels was assessed by determining their net displacement after successive application of the forward and backward DVF. The reconstructed dose based on demons DIR was compared to the ground truth to assess the structure-specific uncertainties of this DIR algorithm for inverse consistent and inverse in consistent voxels. Overall, 98.5% of voxels were inverse consistent with the 95% level of confidence range for dose reconstruction of a single fraction equal to [−2.3%; +2.1%], [−10.2%; +15.2%] and [−9.5%; +12.5%] relative to their planned dose for target structures, critical organs at risk (OARs) and non-critical OARs, respectively. Inverse in consistent voxels generally showed a higher level of uncertainty. The uncertainty in accumulated dose using DIR can be accurately quantified and incorporated in dose-volume histograms (DVHs). This method can be used to prospectively assess the adequacy of target coverage during treatment in an objective manner. [ABSTRACT FROM AUTHOR]

• A method was developed to simultaneously acquire cine imaging and isotropic 4D-MRI. • Super-resolution methods improve the resolution of the 4D-MRIs along the slice dimensions. • Preliminary testing was performed structural and dynamic phantoms and in vivo. • The promising results merit further investigation for use during MR-guided radiotherapy. Effective management of intrafraction motion is critical to the success of MR-guided radiation therapy (MR-gRT) of abdominal or thoracic tumors. Recent developments have proposed the use of cine MRI to monitor motion and 4D-MRI to aid in the reconstruction of dose actually delivered to patients. The present work aims to develop and perform preliminary testing of an imaging framework capable of simultaneously acquiring orthogonal plane cine imaging and isotropic resolution 4D-MRI volumes using super-resolution methods. A pulse sequence was developed to acquire time-locked cine imaging in sagittal and coronal planes while additionally acquiring 4D-MRIs in both planes simultaneously. Isotropic resolution 4D-MRIs were reconstructed by combining information from the orthogonal volumes using super-resolution methods. This method was tested in phantoms and in liver cancer patients. Simultaneous cine imaging in sagittal and coronal planes allowed monitoring of respiratory motion and an accurate binning of concurrently acquired 4D imaging slices into the appropriate respiratory phases. The super-resolution reconstruction methods improved the resolution of the 4D-MRI along both of the low-resolution slice-select dimensions. The development and preliminary testing of an imaging framework capable of acquiring simultaneous orthogonal cine imaging and super-resolution 4D-MRI was performed. The promising results merit further investigation for use in dose reconstruction during MR-guided radiation therapy. [ABSTRACT FROM AUTHOR]

Objectives: To derive conversions of antiquated exposure data into modern equivalents and to apply these in the assessment of the skin dose of pelvic radiographs since 1896. Methods: The literature 1896–2018 was searched for implicit and explicit dose information. The early implicit dose data contained now obsolete descriptions of radiation quality and quantity for long since disappeared X-ray systems of limited efficiency. Converting the old information into modern specifications was achieved using contemporary data and computer simulations. Final dose calculations were done with modern software. Explicit radiation doses of later date reported in old quantities and units were adapted according to current recommendations. Results: For the period before 1927 conversion algorithms for spark gap data and penetrometer hardnesses to high voltage could be derived. Electrical and X-ray efficiencies of several old röntgen systems were determined. Together they allowed reconstruction of 53 doses. After 1927 doses were generally explicitly specified; 114 were retrieved. Although an enormous spread was observed, the average skin dose was reduced by a factor of about 400. Conclusions: Antiquated exposure data were successfully used for dose reconstruction. Extreme dose variability was a constant. Efforts to cut down doses were effective as skin doses went down from sub-erythema values to about one milligray. [ABSTRACT FROM AUTHOR]

Objective. To experimentally validate a method to create continuous time-resolved estimated synthetic 4D-computed tomography datasets (tresCTs) based on orthogonal cine MRI data for lung cancer treatments at a magnetic resonance imaging (MRI) guided linear accelerator (MR-linac). Approach. A breathing porcine lung phantom was scanned at a CT scanner and 0.35 T MR-linac. Orthogonal cine MRI series (sagittal/coronal orientation) at 7.3 Hz, intersecting tumor-mimicking gelatin nodules, were deformably registered to mid-exhale 3D-CT and 3D-MRI datasets. The time-resolved deformation vector fields were extrapolated to 3D and applied to a reference synthetic 3D-CT image (sCT ref ), while accounting for breathing phase-dependent lung density variations, to create 82 s long tresCTs at 3.65 Hz. Ten tresCTs were created for ten tracked nodules with different motion patterns in two lungs. For each dataset, a treatment plan was created on the mid-exhale phase of a measured ground truth (GT) respiratory-correlated 4D-CT dataset with the tracked nodule as gross tumor volume (GTV). Each plan was recalculated on the GT 4D-CT, randomly sampled tresCT, and static sCT ref images. Dose distributions for corresponding breathing phases were compared in gamma (2%/2 mm) and dose-volume histogram (DVH) parameter analyses. Main results. The mean gamma pass rate between all tresCT and GT 4D-CT dose distributions was 98.6%. The mean absolute relative deviations of the tresCT with respect to GT DVH parameters were 1.9%, 1.0%, and 1.4% for the GTV D 98% , D 50% , and D 2% , respectively, 1.0% for the remaining nodules D 50% , and 1.5% for the lung V 20Gy . The gamma pass rate for the tresCTs was significantly larger ( p < 0.01), and the GTV D 50% deviations with respect to the GT were significantly smaller ( p < 0.01) than for the sCT ref . Significance. The results suggest that tresCTs could be valuable for time-resolved reconstruction and intrafractional accumulation of the dose to the GTV for lung cancer patients treated at MR-linacs in the future., (Creative Commons Attribution license.)

Otoliths are the organs which fish use for hearing and keeping balance. Otoliths are the most calcified tissues in the fish body. In contrast to bones, otoliths are not affected by remodeling and, therefore, they are expected to accumulate any dose from ionizing radiation during lifetime. Therefore, EPR dosimetry with fish otoliths could be an important tool for dose reconstruction in radiobiology and radioecology. It could also provide useful information remediation actions to de-contaminate waterbodies. Consequently, in the present study, otoliths of three contaminated fish species (roach (Rutilus rutilus), pike (Esox lucius) and perch (Perca Fluviatilis)) were examined with Electron Paramagnetic Resonance (EPR) spectroscopy. The fish were caught at storage reservoirs of liquid radioactive waste from Mayak PA and from the upper reach of the Techa River, which have been contaminated with different levels of radionuclide activity concentrations. It is shown that the radiation-induced EPR signal of otolith is stable and characterized by a linear dose response. However, the slope of the calibration curve (corresponding to the radiation sensitivity of the material) is not the same for different species; this may be caused by differences in mineralization. The reconstructed doses were found to be in the range from undetectable (in fish from the upper stream of the Techa River) up to 265 Gy (in roach from the most contaminated waterbody). In parallel, otoliths were measured with β-counter to detect 90Sr/90Y. Samples were also tested on the presence of alpha-emitters, but no alpha activity above background could be detected. However, a significant activity concentration of 90Sr was detected (from 1 × 101 to 2 × 104 Bq/g). The EPR doses measured correlated with the 90Sr activity concentration measured in the otolith samples. [ABSTRACT FROM AUTHOR]

Neutron dose coefficients for standard irradiation geometries have been reported in International Commission on Radiological Protection (ICRP) Publication 116 for the ICRP Publication 110 adult reference phantoms. In the present work, organ and effective dose coefficients have been calculated for a receptor in both upright and articulated (bent) postures representing more realistic working postures exposed to a mono-energetic neutron radiation field. This work builds upon prior work by Dewji and co-workers comparing upright and bent postures for exposure to mono-energetic photon fields. Simulations were conducted using the Oak Ridge National Laboratory’s articulated stylized adult phantom, “Phantom wIth Moving Arms and Legs” (PIMAL) software package, and the Monte Carlo N-Particle (MCNP) version 6.1.1 radiation transport code. Organ doses were compared for the upright and bent (45° and 90°) phantom postures for neutron energies ranging from 1 × 10− 9 to 20 MeV for the ICRP Publication 116 external exposure geometries—antero-posterior (AP), postero-anterior (PA), and left and right lateral (LLAT, RLAT). Using both male and female phantoms, effective dose coefficients were computed using ICRP Publication 103 methodology. The resulting coefficients for articulated phantoms were compared to those of the upright phantom. Computed organ and effective dose coefficients are discussed as a function of neutron energy, phantom posture, and source irradiation geometry. For example, it is shown here that for the AP and PA irradiation geometries, the differences in the organ coefficients between the upright and bent posture become more pronounced with increasing bending angle. In the AP geometry, the brain dose coefficients are expectedly higher in the bent postures than in the upright posture, while all other organs have lower dose coefficients, with the thyroid showing the greatest difference. Overall, the effective dose estimated for the upright phantom is more conservative than that for the articulated phantom, which may have ramifications in the estimation or reconstruction of radiation doses. [ABSTRACT FROM AUTHOR]

Although corporate sponsorship of research does not necessarily lead to biased results, in some industries, it has resulted in the publication of inaccurate and misleading data. Some companies have hired scientific consulting firms to retrospectively calculate exposures to hazardous products during use that are no longer manufactured or sold. As an example, this paper reviews one such study—a litigation-generated study of Union Carbide Corporation’s asbestos-containing product, Bakelite®. This analysis is based on previously secret documents, produced as a result of litigation. The study generated asbestos fiber exposure measurements which resulted in underestimates of actual exposures to create doubt about the hazards associated with manufacture and manipulation of Bakelite®. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this work was to assess the feasibility of using surrogate CT scans of matched patients for organ dose reconstructions for childhood cancer (CC) survivors, treated in the past with only 2D imaging data available instead of 3D CT data, and in particular using the current literature standard of matching patients based on similarity in age and gender. Methods: Thirty‐one recently treated CC patients with abdominal CT scans were divided into six age‐ and gender‐matched groups. From each group, two radiotherapy plans for Wilms’ tumor were selected as reference plans and applied to the age‐ and gender‐matched patients’ CTs in the respective group. Two reconstruction strategies were investigated: S1) without field adjustments; S2) with manual field adjustments according to anatomical information, using a visual check in digitally reconstructed radiographs. To assess the level of agreement between the reconstructed and the reference dose distributions, we computed (using a collapsed cone algorithm) and compared the absolute deviation in mean and maximum dose normalized by the prescribed dose (i.e., normalized errors |NEmean| and |NE2cc|) in eight organs at risk (OARs): heart, lungs, liver, spleen, kidneys, and spinal cord. Furthermore, we assessed the quality of a reconstruction case by varying acceptance thresholds for |NEmean| and |NE2cc|. A reconstruction case was accepted (i.e., considered to pass) if the errors in all OARs are smaller than the threshold. The pass fraction for a given threshold was then defined as the percentage of reconstruction cases that were classified as a pass. Furthermore, we consider the impact of allowing to use a different CT scan for each OAR. Results: Slightly smaller reconstruction errors were achieved with S2 in multiple OARs than with S1 (P < 0.05). Among OARs, the best reconstruction was found for the spinal cord (average |NEmean| and |NE2cc| ≤ 4%). The largest average |NEmean| was found in the spleen (18%). The largest average |NE2cc| was found in the left lung (26%). Less than 30% of the reconstruction cases (i.e., pass fraction) meet the criteria that |NEmean| < 20% and |NE2cc| < 20% in all OARs when using age and gender matching and a single CT to do reconstructions. Allowing other matchings and combining reconstructions for OARs from multiple patients, the pass fraction increases substantially to more than 60%. Conclusions: To conclude, reconstructions with small deviations can be obtained by using CC patients’ CT scans, making the general approach promising. However, using age and gender as the only matching criteria to select a CT scan for the reconstruction is not sufficient to guarantee sufficiently low reconstruction errors. It is therefore suggested to include more features (e.g., height, features extracted from 2D radiographs) than only age and gender for dose reconstruction for CC survivors treated in the pre‐3D radiotherapy planning era and to consider ways to combine multiple reconstructions focused on different OARs. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study is to establish the first step toward a novel and highly individualized three‐dimensional (3D) dose distribution reconstruction method, based on CT scans and organ delineations of recently treated patients. Specifically, the feasibility of automatically selecting the CT scan of a recently treated childhood cancer patient who is similar to a given historically treated child who suffered from Wilms’ tumor is assessed. Methods: A cohort of 37 recently treated children between 2‐ and 6‐yr old are considered. Five potential notions of ground‐truth similarity are proposed, each focusing on different anatomical aspects. These notions are automatically computed from CT scans of the abdomen and 3D organ delineations (liver, spleen, spinal cord, external body contour). The first is based on deformable image registration, the second on the Dice similarity coefficient, the third on the Hausdorff distance, the fourth on pairwise organ distances, and the last is computed by means of the overlap volume histogram. The relationship between typically available features of historically treated patients and the proposed ground‐truth notions of similarity is studied by adopting state‐of‐the‐art machine learning techniques, including random forest. Also, the feasibility of automatically selecting the most similar patient is assessed by comparing ground‐truth rankings of similarity with predicted rankings. Results: Similarities (mainly) based on the external abdomen shape and on the pairwise organ distances are highly correlated (Pearson rp ≥ 0.70) and are successfully modeled with random forests based on historically recorded features (pseudo‐R2 ≥ 0.69). In contrast, similarities based on the shape of internal organs cannot be modeled. For the similarities that random forest can reliably model, an estimation of feature relevance indicates that abdominal diameters and weight are the most important. Experiments on automatically selecting similar patients lead to coarse, yet quite robust results: the most similar patient is retrieved only 22% of the times, however, the error in worst‐case scenarios is limited, with the fourth most similar patient being retrieved. Conclusions: Results demonstrate that automatically selecting similar patients is feasible when focusing on the shape of the external abdomen and on the position of internal organs. Moreover, whereas the common practice in phantom‐based dose reconstruction is to select a representative phantom using age, height, and weight as discriminant factors for any treatment scenario, our analysis on abdominal tumor treatment for children shows that the most relevant features are weight and the anterior–posterior and left–right abdominal diameters. [ABSTRACT FROM AUTHOR]

Purpose Until now, real-time image guided adaptive radiation therapy (IGART) has been the domain of dedicated cancer radiotherapy systems. The purpose of this study was to clinically implement and investigate real-time IGART using a standard linear accelerator. Materials/methods We developed and implemented two real-time technologies for standard linear accelerators: (1) Kilovoltage Intrafraction Monitoring (KIM) that finds the target and (2) multileaf collimator (MLC) tracking that aligns the radiation beam to the target. Eight prostate SABR patients were treated with this real-time IGART technology. The feasibility, geometric accuracy and the dosimetric fidelity were measured. Results Thirty-nine out of forty fractions with real-time IGART were successful (95% confidence interval 87–100%). The geometric accuracy of the KIM system was −0.1 ± 0.4, 0.2 ± 0.2 and −0.1 ± 0.6 mm in the LR, SI and AP directions, respectively. The dose reconstruction showed that real-time IGART more closely reproduced the planned dose than that without IGART. For the largest motion fraction, with real-time IGART 100% of the CTV received the prescribed dose; without real-time IGART only 95% of the CTV would have received the prescribed dose. Conclusion The clinical implementation of real-time image-guided adaptive radiotherapy on a standard linear accelerator using KIM and MLC tracking is feasible. This achievement paves the way for real-time IGART to be a mainstream treatment option. [ABSTRACT FROM AUTHOR]

• The framework for a Monte Carlo based 4D dose reconstruction method is presented. • This method is demonstrated on 2 patients receiving curative lung cancer treatments. • Respiratory traces and log files were collected for 5 fractions for each patient. • Small differences were noted between the reconstructed doses and the planned doses. To investigate the feasibility of a 4D Monte Carlo based dose reconstruction method to study the dosimetric impact of respiratory motion using surface motion measurements for patients undergoing VMAT treatments for Non-Small Cell Lung Cancer. The 4Ddefdosxyznrc/EGSnrc algorithm was used to reconstruct VMAT doses delivered to the patients using machine log files and respiratory traces measured with the RADPOS 4D dosimetry system. The RADPOS sensor was adhered to the patient's abdomen prior to each treatment fraction and its position was used as a surrogate for tumour motion. Treatment log files were synchronized with the patient respiratory traces. Patient specific respiratory models were generated from deformable registration of the inhale and exhale 4DCT images and the respiratory traces. The reconstructed doses were compared to planned doses calculated with DOSXYZnrc/EGSnrc on the average-intensity and the exhale phase CT images. Respiratory motion measurements and log files were acquired for 2 patients over 5 treatment fractions each. The motion was predominantly along the anterior/posterior direction (A/P). The average respiratory amplitudes were 8.7 ± 2.7 mm and 10.0 ± 1.2 mm for Patient 1 and 2, respectively. Both patients displayed inter- and intra-fractional variations in the baseline position. Small inter-fractional differences were observed in the reconstructed doses for each patient. Differences between the reconstructed and planned doses were attributed to differences in organ volumes. The 4D reconstruction method was successfully implemented for the two patients studied. Small differences between the planned and reconstructed doses were observed due to the small tumour motion of these patients. [ABSTRACT FROM AUTHOR]