S2406
Physics - Quality assurance and auditing
ESTRO 2026
Digital Poster Highlight 4977 Validation of intercomparison testing for international clinical trial QA group multi-target SRS audit reciprocity Mallory C. Glenn 1 , Jessica Lye 2,3 , Catharine Clark 4 , Fayz Kadeer 2 , Hannah Cook 4 , Ileana Silvestre Patallo 4 , Stephen Kry 1 , Joerg Lehmann 5,6 1 Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, USA. 2 Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia. 3 Radiation Oncology, Austin Health, Heidlberg, Australia. 4 Radiotherapy and Radiation Dosimetry Group, National Physical Laboratory, Teddington, United Kingdom. 5 Radiation Oncology, Cavalry Mater Newcastle, Waratah, Australia. 6 School of Information and Physical Sciences, University of Newcastle, Newcastle, Australia Purpose/Objective: One goal of the Radiotherapy Clinical Trials QA Global Harmonization Group (GHG) is to harmonize audits across its member groups. In order to establish reciprocity of dosimetry audits, a cross-validation of the audit performance is necessary. This work describes a proof-of-concept to cross-validate respective single-iso/multi-lesion SRS treatments. Material/Methods: An in-house high impact polystyrene phantom (CubeRT) was developed to accommodate point dose measurements for both a PTW MicroDiamond and an Exradin A16 small volume ion chamber to validate dose delivery. Three treatment plans were designed following the protocol for the ACDS Level III SRS audit, including both single and multi-target cases of varying delivery strategies and complexity. Plans were copied onto CubeRT and measurements in two targets were made to validate the underlying accuracy of the plans (aligned with recommendations from upcoming AAPM TG reports 360 and 362). Validation measurements were performed with both small field detectors, which had traceability to two separate primary standards dosimetry laboratories, increasing the robustness of the validation. The plans were then also calculated and delivered to the ACDS customized MAX-HD SRS phantom to evaluate audit agreement.
The on-site audits continue to identify clinical shortcomings and QA deficiencies. In the last five years, each proton center received an average of 3 recommendations for program improvement. Figure 2 shows gamma analyses for a patient-specific QA measurement performed by IROC and compared with the clinical TPS data. The original dose calculation from the pencil beam algorithm had a pass rate of only 72% of pixels, while the Monte Carlo recalculation passed 100% of pixels. This result was from an audit performed in 2025, which highlights that despite wide community knowledge of technological advances, there is a continued need for practice improvement.
Conclusion: Despite several decades of clinical proton therapy experience, proton therapy audits continue to identify clinically relevant dosimetric errors and areas for practice improvement. As new centers open and new technologies are implemented, they can benefit from external audits to ensure proper implementation and accurate proton therapy treatment. Keywords: proton therapy, audits, peer review
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