ESTRO 2025 - Abstract Book

S3579

Physics - Quality assurance and auditing

ESTRO 2025

59

Digital Poster Feasibility of independent calculation-based dose for patient specific quality assurance in pencil beam scanning proton therapy Nichakan Chatchumnan, Mananchaya Vimolnoch, Sakda Kingkaew, Puntiwa Oonsiri, Sornjarod Oonsiri Radiology, King Chulalongkorn Memorial Hospital, Bangkok, Thailand Purpose/Objective: Measurement-based in patient-specific quality assurance (PSQA) is essential process in proton therapy but time consuming and require extensive resources. Currently, an independent dose calculation using Monte Carlo (MC) simulations offers a promising alternative tool. The aim of this study is to investigate the feasibility of independent dose calculation for PSQA in pencil beam scanning proton therapy and establish confidence limits, tolerance limits, and action limits. Material/Methods: Independent dose calculations were performed using the IBA myQA iON software version 2.1, and the accuracy was validated against ionization chamber with step of energy 70, 100, 130, 160, 190, and 200 MeV. Dose distributions from myQA iON were compared with Varian Eclipse treatment planning system (TPS) version 16.1, using the convolution superposition algorithm for single and multiple energy plans. A total of 72 clinical plans, covering five anatomical regions (head and neck, breast, chest, abdomen, and pelvis), were analyzed by gamma analysis with 3%/3 mm and 5%/3 mm criteria. The confidence limits, tolerance limits, and action limits were determined according AAPM TG-119 and TG-218. Results: The dose differences between measurements and independent dose calculations for each energy level were accurate within 1.0%. Gamma passing rates were 99.4 ± 0.6% for single energy and 99.1± 1.1% for multiple energy. The example of independent dose calculation is shown in Figure 1. For all treatment sites, the average gamma passing rate was 95.8 ± 3.1% using the 3%/3 mm, which improved to 97.7 ± 2.3% with 5%/3 mm. The confidence limits, tolerance limits, and action limits are presented in Table 1. The maximum and minimum confidence limit were observed in pelvis and chest region, respectively.