Abstract:Online adaptive radiotherapy platforms present a unique challenge for commissioning as guidance is lacking and specialized adaptive equipment, such as deformable phantoms, are rare. We designed a novel adaptive commissioning process consisting of end‐to‐end tests using standard clinical resources. These tests were designed to simulate anatomical changes regularly observed at patient treatments. The test results will inform users of the magnitude of uncertainty from on‐treatment changes during the adaptive work… Show more
“…In this time period, abdominopelvic air cavities may migrate, expand, or disappear, rendering the time‐consuming manual corrections invalid. Our results are in concordance with previous studies that investigated the dosimetric effects of electron density correction for MR‐based oART 29 and gas overrides in a phantom‐base commissioning of the Ethos workflow 30 . Both studies agreed that manual correction of air volume is time consuming and has minimal clinical effect in the dose distribution.…”
PurposeCBCT‐guided online adaptive radiotherapy (oART) plans presently utilize daily synthetic CTs (sCT) that are automatically generated using deformable registration algorithms. These algorithms may have poor performance at reproducing variable volumes of gas present during treatment. Therefore, we have analyzed the air mapping error between the daily CBCTs and the corresponding sCT and explored its dosimetric effect on oART plan calculation.MethodsAbdominopelvic air volume was contoured on both the daily CBCT images and the corresponding synthetic images for 207 online adaptive pelvic treatments. Air mapping errors were tracked over all fractions. For two case studies representing worst case scenarios, dosimetric effects of air mapping errors were corrected in the sCT images using the daily CBCT air contours, then recalculating dose. Dose volume histogram statistics and 3D gamma passing rates were used to compare the original and air‐corrected sCT‐based dose calculations.ResultsAll analyzed patients showed observable air pocket contour differences between the sCT and the CBCT images. The largest air volume difference observed in daily CBCT images for a given patient was 276.3 cc, a difference of more than 386% compared to the sCT. For the two case studies, the largest observed change in DVH metrics was a 2.6% reduction in minimum PTV dose, with all other metrics varying by less than 1.5%. 3D gamma passing rates using 1%/1 mm criteria were above 90% when comparing the uncorrected and corrected dose distributions.ConclusionCurrent CBCT‐based oART workflow can lead to inaccuracies in the mapping of abdominopelvic air pockets from daily CBCT to the sCT images used for the optimization and calculation of the adaptive plan. Despite the large observed mapping errors, the dosimetric effects of such differences on the accuracy of the adapted plan dose calculation are unlikely to cause differences greater than 3% for prostate treatments.
“…In this time period, abdominopelvic air cavities may migrate, expand, or disappear, rendering the time‐consuming manual corrections invalid. Our results are in concordance with previous studies that investigated the dosimetric effects of electron density correction for MR‐based oART 29 and gas overrides in a phantom‐base commissioning of the Ethos workflow 30 . Both studies agreed that manual correction of air volume is time consuming and has minimal clinical effect in the dose distribution.…”
PurposeCBCT‐guided online adaptive radiotherapy (oART) plans presently utilize daily synthetic CTs (sCT) that are automatically generated using deformable registration algorithms. These algorithms may have poor performance at reproducing variable volumes of gas present during treatment. Therefore, we have analyzed the air mapping error between the daily CBCTs and the corresponding sCT and explored its dosimetric effect on oART plan calculation.MethodsAbdominopelvic air volume was contoured on both the daily CBCT images and the corresponding synthetic images for 207 online adaptive pelvic treatments. Air mapping errors were tracked over all fractions. For two case studies representing worst case scenarios, dosimetric effects of air mapping errors were corrected in the sCT images using the daily CBCT air contours, then recalculating dose. Dose volume histogram statistics and 3D gamma passing rates were used to compare the original and air‐corrected sCT‐based dose calculations.ResultsAll analyzed patients showed observable air pocket contour differences between the sCT and the CBCT images. The largest air volume difference observed in daily CBCT images for a given patient was 276.3 cc, a difference of more than 386% compared to the sCT. For the two case studies, the largest observed change in DVH metrics was a 2.6% reduction in minimum PTV dose, with all other metrics varying by less than 1.5%. 3D gamma passing rates using 1%/1 mm criteria were above 90% when comparing the uncorrected and corrected dose distributions.ConclusionCurrent CBCT‐based oART workflow can lead to inaccuracies in the mapping of abdominopelvic air pockets from daily CBCT to the sCT images used for the optimization and calculation of the adaptive plan. Despite the large observed mapping errors, the dosimetric effects of such differences on the accuracy of the adapted plan dose calculation are unlikely to cause differences greater than 3% for prostate treatments.
“…Before each treatment session, the presence of gas on CBCT is vigilantly monitored or removed, if deemed necessary. This approach is consistent with the investigation conducted by Kisling et al 10 Figure 3 Comparison of CBCT and synthetic CT images with (A) biliary stent, (B) air bubbles, and (C) bolus. (A) The purple-colored high-density structure from the synthetic CT overlaps with the biliary stent on the CBCT, enabling acceptable dose calculation.…”
Section: Methodssupporting
confidence: 88%
“…Despite a few published articles on commissioning and dosimetric studies of the CBCT-based OART platform, 9 , 10 , 11 , 12 , 13 a pressing need remains for published guidance on the comprehensive treatment workflow and individual responsibilities. In this study, we conducted a failure mode and effects analysis (FMEA) to identify high-risk failure modes and developed logistically feasible clinical workflows for OART, which are categorized into 4 components: 1 site-specific templates preparation, 2 pretreatment planning and verification, 3 on-treatment procedures, and 4 posttreatment verification, along with safety checklists.…”
“…Kisling et al observed an average of 1.6% difference between phantom ion chamber measurements and synthetic CT doses, even when simulating weight losses and gains of up to 4 cm, which are more extreme than the differences expected in this study. 26 Additionally, Nelissen et al observed <2% dose disparity between the synthetic CT and CBCT in high dose regions for palliative spine treatment. 27 Although smaller calculation grids are preferred for SBRT plans, the Ethos platform (v1.1 MR3) offers a minimum optimization and dose calculation resolution of 2.5 mm at this time.…”
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