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A method for performing film dosimetry as part of a postal audit service by a recalibration process
No full textA method for performing film dosimetry as part of a postal audit service by a recalibration process TOTAL CHARACTERS TITLE: 99 (limit 100 characters) TOTAL CHARACTERS ABSTRACT INCLUDING SPACE: 578+946+769+609 = 2902 (limit 3000 characters including space) Purpose/Objective (578 characters with space) We perform postal dosimetry audits using alanine/EPR and film dosimetry. For postal audits, it is very difficult to control the time window between scanning and irradiation. The films should also be possible to rescan if required even after very long times (order of years). This work evaluates our procedure wherein we compensate for the time delay and various scanner effects using the "one-scan" method (1). We investigated for post-exposure changes, lot-to-lot variability, different dose-response functions and the necessity of accuracy of the delivered dose for rescaling. Material and Methods (946 characters with space) In the context of an audit, the centres irradiated an anthropomorphic phantom that contained EBT3 film and alanine detectors with an IMRT/VMAT plan. Besides, they irradiated a PMMA plate containing film and alanine detectors in contact with each other using a uniform field at a dose similar to the dose prescribed in the VMAT plan. This film was used to rescale the film calibration curve. Films from previous audits were rescanned multiple times and compared to the patient plans and the dose maps of the original scans. Dose maps were generated from films of 4 different lots with one of the lots having a different marker dye. Two dose-response functions were used for the calibration of 3 of the 4 lots. The calibration curve of the last lot was only possible to fit with one of the functions. The sensitivity of the rescaling dose was investigated by recalculating the dose maps with artificially altered doses for the rescaling films. Results (769 characters with space) For the comparison to the patient plans, the passing rates are nearly unchanged (≥ 99%) using gamma analysis with 3%/3mm (Table 1) for the different scan times and using different lots. The only exception is lot C3 that could only be fitted with a cubic function. Some deviations are observed when the cubic function is used and when the marker dye of the calibration and test films is different. The passing rates were unchanged when the rescaling dose was altered by 1% but started to fluctuate when the dose was altered by 2%. The dose maps were compared with each other using gamma analysis with 2%/2mm. The passing rates are ≥ 99% with the exception of lot C3 and using the cubic function with lots having a different marker dye for the calibration and test films. Conclusion (609 characters with space) We showed that it is possible to use film dosimetry for postal audit services using a rescaling method. These results show that it might be possible to use a generic calibration curve for EBT3 films in combination with the rescaling method. Users must however be careful not to mix film lots that have a different marker dye and a different dose-response function. The delivered dose to the calibration films should be determined with an accuracy of ≤1%
Results of the remote Belgian dosimetry audits for lung SBRT
No full textFor Eclipse users only TGI correlated with the dosimetry audit data, where a higher TGI gave poorer QA results (see Figure 2). The Pearson correlation coefficients of alanine and film dose vs TGI were r = 0.491 and 0.564 respectively. Conclusion In general, the complexity of benchmark and audit plans was found to be comparable, with no statistically significant difference in complexity observed for 4 of the 5 CMs evaluated. MDLG was significantly higher in the benchmark plans, which may be attributed to the larger target volume in this plan. This indicates the audit programme is testing plans of comparable complexity to the clinical benchmark case. TGI showed moderate correlation with the dosimetry audit results. This may be used to assess the dosimetry audit plan before measurements are undertaken to ensure that potential outliers are identified before audit measurements are undertaken. MO-0307 Results of the remote Belgian dosimetry audits for lung SBRT Purpose or Objective NuTeC is performing remote dosimetry audits for lung SBRT in Belgium using alanine/EPR and radiochromic film dosimetry. The goal is to provide an independent assessment of the dosimetric accuracy for the SBRT practice of the hospitals in Belgium. Materials and Methods The centres receive the audit material and the DICOM data beforehand. The audit consists of a series of basic tests in water and solid water and an E2E test for a lung SBRT case on a commercial lung phantom preloaded with detectors. The alanine detectors had an uncertainty of 1 %. Both detectors are calibrated in dose-to-water (Dw). Consequently the centres using Acuros had to provide the dose calculations in Dw instead of dose-to-medium (Dm). The tumour volume is simulated using a 3D printed mould filled with a silicone mixture. An alanine pellet is placed in the centre of this tumour volume. Large film detectors (EBT-XD) are placed through the target in the lung equivalent material and also on top of the lungs. The comparisons of film to plans were done using gamma analysis with global normalisation and 10 % threshold. Our alanine/EPR dosimetry was also validated by the IAEA for multiple photon beams. Result
Early results of a remote dosimetry audit program for lung stereotactic body radiation therapy
No full textBackground and purpose: A dosimetry audit program based on alanine electron paramagnetic resonance (EPR) and radiochromic film dosimetry, may be a valuable tool for monitoring and improving the quality of lung stereotactic body radiotherapy (SBRT). The aim of this study was to report the initial, independent assessment of the dosimetric accuracy for lung SBRT practice using these dosimeters in combination with a novel phantom design. Materials and Methods: The audit service was a remote audit program performed on a commercial lung phantom preloaded with film and alanine detectors. An alanine pellet was placed in the centre of the target simulated using silicone in a 3D-printed mould. Large film detectors were placed coronally through the target and the lung/ tissue interface and analysed using gamma analysis. The beam output was always checked on the same day with alanine dosimetry in water. We audited 29 plans from 14 centres up to now. Results: For the alanine results 28/29 plans were within 5 % with 19/29 plans being within 3 %. The passing rates were > 95 % for the film through the target for 27/29 plans and 17/29 plans for the film at the lung/tissue interface. For three plans the passing rate was < 90 % for the film on top of the lungs. Conclusions: The preliminary results were very satisfactory for both detectors. The high passing rates for the film in the interface region indicate good performance of the treatment planning systems. The phantom design was robust and performed well on several treatment systems.The BELdART project is sponsored by the Cancer Plan and was monitored by the Belgian College of Radiation Oncology between 2009- 2022
BELgian dosimetry Audits in RadioTherapy
No full textPurpose: Independent dosimetry audits are crucial for the QA of radiotherapy departments. The Nuclear Technology Centre (NuTeC) is performing dosimetry audits since 2009 in Belgium and occasionally in some neighbouring countries. The BELdART project started when the Belgian Federal Agency for Nuclear Control (FANC/AFCN) requested a national audit program for reference and non-reference conditions with support from the Cancer plan. During 2009-2011, all Belgian clinics participated in the dosimetry audits for standard static fields. Then in 2012, auditing of more sophisticated techniques was introduced such as IMRT, Arc therapy and Tomotherapy. In 2017, an audit program for intracranial SRS was developed and later for lung SBRT early in 2020. Additionally, NuTeC also provides external audits upon request from the clinics. Materials and Methods: A combination of alanine/EPR and film dosimetry is used for the dose measurements, the alanine being used for point dosimetry and the film for evaluating 2D dose distributions. The audits are composed of basic dosimetric checks in water and solid water with alanine pellets and End-To-End (E2E) tests on an anthropomorphic phantom containing film/alanine detectors. The films are analysed with 3-channel dosimetry. All measurements for a beam are performed on the same day to allow identifying the source of possible problems during the E2E test. Since 2012, the audits are entirely mailed. Results: 61/91 machines were audited during 2009-2011 with 60/61 of the machines having acceptable parameters and for the dosimetric evaluation, all the 212 beams were within 5%. During 2012-2016, 33 beams were audited for IMRT/Arc treatment on a prostate case. 87.9% and 78.8% of the beams were within 3% for the alanine pellets placed in the prostate and seminal vesicles regions respectively. For the gamma analysis with the films with 3%/3mm criteria, 97% of the films had a passing rate higher than 95%. For the intracranial SRS audits, 16 beams were audited up to now with 68.8% of the beams being within 3% for the alanine measurement. For the films with 5%1mm criteria for the gamma analysis, 15/16 had a passing rate higher than 90%. 2 lung SBRT audits are performed at the time of writing. Conclusions: The BELdART team continues to provide dosimetry auditing services to the radiotherapy community in Belgium. The results up to now show that in general, the dosimetric accuracy in Belgian clinics is very good for the different audited techniques
BELdART: Belgian dosimetry audits in radiotherapy
No full textPurpose: Contemporary external radiotherapy requires the outmost precision in patient positioning. This can be achieved through 2D/3D image acquisition by the on-board imager (OBI) integrated into the linear accelerator. In this study, OBI 2D image acquisition protocols were assessed and optimized with regard to dose in an effort to reduce overall patient dose without degrading kV image quality. Materials and Methods: A phantom for high/low spatial resolution assessment was placed at the center of appropriately compiled PMMA plates to serve as cephalic (19cmX17cm) and pelvic (24cmX37cm) phantoms. Anterior-posterior and lateral scanning of the phantoms was carried out using the predefined/default acquisition protocols to assess image quality and measure the entrance dose utilizing a low dose rate probe. Anterior-posterior and lateral images were then acquired for all available kV/mAs configurations and corresponding entrance dose were recorded. An experienced user rejected all protocols that produced images with quality inferior to that achieved by the default protocol. The optimized head and pelvis protocols were selected as those corresponding to the lowest doses. A Rando phantom was scanned with both default and dose-optimized protocols, while proposed protocols were used for intra-session imaging in 10 patients. A physician employed a 5-point scale to subjectively assess quality of Rando and patient images. Effective doses were estimated in an average-sized anthropomorphic model for default and optimized acquisitions. Results: Low spatial resolution exhibited a strong dependence on kV/mAs settings, in contradistinction to high spatial resolution. Optimized head protocols for anterior-posterior/lateral scans employed 80/60 kVp and 6.4/5.0 mAs, whilst proposed pelvis protocols for anterior-posterior/lateral acquisitions utilized 80/100 kVp and 6.25/64.0 mAs. In comparison to the default parameters, the implementation of optimized settings resulted in 49% and 29% entrance dose reduction in the cephalic anterior-posterior and lateral scans, respectively, and in 29% and 27% entrance dose reduction in the pelvic anterior-posterior and lateral acquisitions, respectively. Quality of Rando images acquired with proposed protocols was equivalent to that of default protocols. Quality of patient images obtained with optimized settings was graded at least as acceptable, indicating that proposed settings may be routinely used. Optimized protocols were found to decrease effective dose by 27.5% and 49% in pelvic and cephalic acquisitions, respectively. Conclusions: Considering the relatively large number of radiotherapy sessions and consequently of image acquisitions, it is postulated that dose-optimized kV protocols may contribute towards a significant reduction in the overall patient radiation dose without compromising positioning accuracy. P101 Implementation and clinical validation of an atlas based auto segmentation method of head and neck radiotherapy volumes of interest Purpose: To implement and validate an atlas based segmentation method for the automatic contouring of organ at risks (OARs) in the frame of head and neck radiotherapy planning. In this context, an accurate and standardized delineation of OARs is required to face the challenge posed by the location of many critical organs in close proximity to target volumes and the high focalized dose distributions. The atlas can help to speed up the planning workflow, partially replacing manual segmentation, and reduce the intra-and inter-operator dependence improving the standardization process. Materials and Method: In this study, an auto-segmentation method with a "Medium-Atlas" approach was implemented. The atlas consisted of twenty datasets of head and neck radiotherapy patients. The optimization and validation of the method were carried out by comparing the results of the automatic segmentation with those of the manual one. The comparison was carried out on a group of ten datasets belonging to the same institution from which the atlas was built and on a group of ten patients provided by another center. The comparison was made using the following quantitative metrics: Dice similarity index (DSC), average distance to agreement (MDC), sensitivity and positive predictive value (PPV). Results: The number of the ATLAS datasets used to build the medium atlas significantly affects the quality of the segmented contours on the test images (ANOVA: F = 2,96, p <0,05): the optimal number for the accuracy of delineation is N=5. The results of the analysis showed that the automatic segmentation method was accurate for OAR volumes higher than 10 cc: DSC=0,82±0,01, sensitivity=0,74±0,01, PPV=0,92±0,01 and MDC=2,77±0,06 mm. For volumes less than 10 cc the agreement between automatic and manual segmentation worsened and were deemed unsatisfactory. Time consuming was reduced by 50% compared to the manual segmentation. The atlas also showed good performances in its multi-institutional application: for volumes greater than 10 cc: DSC=0,77±0,04, sensitivity=0,83±0,04, PPV=0,75±0,05 and MDC=2,62±0,06 mm; the method does not show statistically significant differences with its mono center application (p=0.43, =0,05). Conclusions: The implemented atlas-based auto-segmentation, in both tested applications, was found to be an efficient and accurate method in the delineation of OARs with volumes greater than 10 cc
BELgian dosimetry Audits in RadioTherapy
No full textPurpose: Independent dosimetry audits are crucial for the QA of radiotherapy departments. The Nuclear Technology Centre (NuTeC) is performing dosimetry audits since 2009 in Belgium and occasionally in some neighbouring countries. The BELdART project started when the Belgian Federal Agency for Nuclear Control (FANC/AFCN) requested a national audit program for reference and non-reference conditions with support from the Cancer plan. During 2009-2011, all Belgian clinics participated in the dosimetry audits for standard static fields. Then in 2012, auditing of more sophisticated techniques was introduced such as IMRT, Arc therapy and Tomotherapy. In 2017, an audit program for intracranial SRS was developed and later for lung SBRT early in 2020. Additionally, NuTeC also provides external audits upon request from the clinics. Materials and Methods: A combination of alanine/EPR and film dosimetry is used for the dose measurements, the alanine being used for point dosimetry and the film for evaluating 2D dose distributions. The audits are composed of basic dosimetric checks in water and solid water with alanine pellets and End-To-End (E2E) tests on an anthropomorphic phantom containing film/alanine detectors. The films are analysed with 3-channel dosimetry. All measurements for a beam are performed on the same day to allow identifying the source of possible problems during the E2E test. Since 2012, the audits are entirely mailed. Results: 61/91 machines were audited during 2009-2011 with 60/61 of the machines having acceptable parameters and for the dosimetric evaluation, all the 212 beams were within 5%. During 2012-2016, 33 beams were audited for IMRT/Arc treatment on a prostate case. 87.9% and 78.8% of the beams were within 3% for the alanine pellets placed in the prostate and seminal vesicles regions respectively. For the gamma analysis with the films with 3%/3mm criteria, 97% of the films had a passing rate higher than 95%. For the intracranial SRS audits, 16 beams were audited up to now with 68.8% of the beams being within 3% for the alanine measurement. For the films with 5%1mm criteria for the gamma analysis, 15/16 had a passing rate higher than 90%. 2 lung SBRT audits are performed at the time of writing. Conclusions: The BELdART team continues to provide dosimetry auditing services to the radiotherapy community in Belgium. The results up to now show that in general, the dosimetric accuracy in Belgian clinics is very good for the different audited techniques
MO-0307 Results of the remote Belgian dosimetry audits for lung SBRT
No full textFor Eclipse users only TGI correlated with the dosimetry audit data, where a higher TGI gave poorer QA results (see Figure 2). The Pearson correlation coefficients of alanine and film dose vs TGI were r = 0.491 and 0.564 respectively. Conclusion In general, the complexity of benchmark and audit plans was found to be comparable, with no statistically significant difference in complexity observed for 4 of the 5 CMs evaluated. MDLG was significantly higher in the benchmark plans, which may be attributed to the larger target volume in this plan. This indicates the audit programme is testing plans of comparable complexity to the clinical benchmark case. TGI showed moderate correlation with the dosimetry audit results. This may be used to assess the dosimetry audit plan before measurements are undertaken to ensure that potential outliers are identified before audit measurements are undertaken. MO-0307 Results of the remote Belgian dosimetry audits for lung SBRT Purpose or Objective NuTeC is performing remote dosimetry audits for lung SBRT in Belgium using alanine/EPR and radiochromic film dosimetry. The goal is to provide an independent assessment of the dosimetric accuracy for the SBRT practice of the hospitals in Belgium. Materials and Methods The centres receive the audit material and the DICOM data beforehand. The audit consists of a series of basic tests in water and solid water and an E2E test for a lung SBRT case on a commercial lung phantom preloaded with detectors. The alanine detectors had an uncertainty of 1 %. Both detectors are calibrated in dose-to-water (Dw). Consequently the centres using Acuros had to provide the dose calculations in Dw instead of dose-to-medium (Dm). The tumour volume is simulated using a 3D printed mould filled with a silicone mixture. An alanine pellet is placed in the centre of this tumour volume. Large film detectors (EBT-XD) are placed through the target in the lung equivalent material and also on top of the lungs. The comparisons of film to plans were done using gamma analysis with global normalisation and 10 % threshold. Our alanine/EPR dosimetry was also validated by the IAEA for multiple photon beams. Result
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