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Validation of a Fast Monte Carlo Code for Patient QA with Clinical Mini and Standard Proton Beams

V Moskvin1*, A Faught1, F Pirlepesov1, S Al-Ward1, S Wilburn1, M Lowe1, M Cohilis2, K Souris2, C Hua1, (1) St. Jude Children's Hospital, Memphis, TN, ,(2) University Catholique De Louvain, Brussels, WBR, BE

Presentations

PO-GePV-T-137 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Fast Monte Carlo codes such as MCsquare can serve as an independent dose verification platform in a patient-specific quality assurance (QA) program. The purpose of this study is to validate our developed models of the clinical mini and standard proton beams.

Methods: Two-dimensional absorbed doses, measured with the MatriXX PT ionization chamber array at multiple depths per field as a part of routine patient QA, were compared to MCsquare calculated doses using a three-dimensional gamma analysis tool and those calculated by a previously developed spot scanning beam model with the TOol for PArticle therapy Simulations (TOPAS). The acceptance threshold was set to 3%/3mm with a 90% passing rate. Tested patient treatment fields were selected to include those with and without the use of a range shifter and a variety of field sizes, depths, modulations, and anatomic locations (brain, abdomen, lung, and extremities).

Results: A total of 202 measurements of 94 treatment fields were compared to MCsquare and TOPAS calculations. The patterns of the passing rates in gamma analysis are similar between TOPAS and MCsquare. The passing rate histogram has a sharp peak at 100% and tapers toward 93% for the main beam option with or without a range shifter. Two cases with the range shifter had a passing rate <93% for both TOPAS and MCsquare. It was contributed to shallow depths of measurement in high dose gradient regions. The passing rate for the mini-beam was 100% for both sets of calculations. The simulation time of MCsquare varies between 1 and 25 min for the used fields.

Conclusion: Good agreement between measured data and MCsquare calculated doses were observed. Results were compared favorably with similar analyses using TOPAS. The use of MCsquare as a patient-specific QA tool for independent dose verification is well supported in our patient cohort.

Keywords

Protons, Monte Carlo, Quality Assurance

Taxonomy

TH- External Beam- Particle/high LET therapy: Carbon ion therapy – computational dosimetry-Monte Carlo

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