S1988
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Results: The results are shown in the table. The average RADAR results with uncertainty are tabulated relative to the canonical results (no uncertainty) as are the doses reported on the SPC. The minimum reported doses are comparable to the canonical values as expected with some slightly lower because the structure specific uncertainty result can sometimes be lower than the canonical result. For spine, the maximum reported doses are typically equal to the global uncertainty results except for cauda which did not always include the global results due to contouring inconsistencies between courses. For lung, the maximum reported results were on average lower than the global results which is less conservative than spine. For brain, a 2mm global uncertainty was standard with few exceptions, therefore the maximum reported results were generally equal to the global results.
Conclusion: Our study showed single-center models have limited capacity to detect cases requiring improvements. External and multicentric validations, incorporating broader geometric variability and treatment strategies, identified cases appearing acceptable within single institutions but deviating from multi-institutional standards. Keywords: KBP, Plan quality, Dose prediction Digital Poster 4255 Increasing the safety of reirradiations: incorporating registration uncertainty into dose accumulation using RADAR James Mechalakos, Yu-Chi Hu, Lei Zhang, Licheng Kuo, Niral Shah, Jeho Jeong, Ellen Yorke, Yilin Liu, Ase Ballangrud, Sebastian Meyer, Laura Cervino, Jean Moran, Joseph Deasy, Nicolas Cote, Phillip Lichtenwalner, Laura Accomando, Peter Florio, Shira Abraham, Pengpeng Zhang Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA Purpose/Objective: To report on the initial clinical implementation of RADAR (RAdiotherapy Dose Accumulation Routine) by comparing dose indices calculated with and without uncertainty. Material/Methods: A review of clinical reirradiation cases for which a dose accumulation was performed using RADAR, an in- house script which can incorporate uncertainty directly into the dose accumulation using a voxel-wise ellipsoid search method, is presented. A total of 24 spine, 19 lung, and 23 brain dose accumulations were reviewed. Accumulations were expressed in 2 Gy equivalent dose (EQD2) using a/b=2 Gy for CNS OAR’s, 3 Gy for all other OAR’s. No tissue recovery factors were applied. RADAR applies uncertainty in 3 ways: zero uncertainty which represents a standard or “canonical” dose accumulation, global uncertainty which is the most conservative (typically 2-3mm for CNS structures, 3-5 mm for other structures), and structure specific uncertainty which constrains the added uncertainty to within a structure of interest. This is most useful when the corresponding global uncertainty result is overly influenced by a nearby target. Based on analysis of these 3 results a range of doses is reported for each index on the special physics consultation form (SPC) after review with the physician. For this study, we compared the RADAR results without uncertainty (canonical) to those with uncertainty for relevant indices associated with the 3 disease sites. We also compared the doses reported on the SPC to the RADAR results for the same indices.
Conclusion: Incorporation of registration uncertainty into
reirradiation planning increases confidence in the safety of reirradiation by allowing review of a range of accumulated dose for comprehensive evaluation by the treatment team, thereby guiding decision making. Keywords: reirradiation, dose accumulation Digital Poster 4268 Absorbed dose uncertainties due to delivery variations and different dose calculation methods Emmanouil Terzidis 1,2 , Fredrik Norström 2,1 , Magnus Gustavsson 2 , Anna Karlsson 1,2 , Julia Götstedt 1,2 , Anna Bäck 1,2 1 Department of Medical Radiation Sciences, Institute of Clinical Sciences, Gothenburg, Sweden. 2 Department of Therapeutic Radiation Physics, Biomedical Engineering and Medical Physics, Gothenburg, Sweden Purpose/Objective: Modulated treatment delivery techniques, such as VMAT, often involve small and irregular beam
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