ESTRO 2025 - Abstract Book

S2641

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

Material/Methods: Treatment plans were calculated in Monaco v. 6.1.4.0 (Elekta) for cohort of 20 patients diagnosed with prostate cancer. Two full, double or single arcs, with energy 6 MV were used. All plans were recalculated onto Ruby's Phantom (PTW) geometry. Dose at point calculated or measured for each of method passed the acceptance criteria, if dose differences were lower than 5% from TPS. The RadCalc (Lifeline Software Inc.) software, using the Clarkson algorithm, was used to recalculate dose at isocenter point as independent system. The software utilize linear accelerator parameters, for example positions and transmission of multileaf collimator, percent depth dose or tissue phantom ratio. The dose at point was also measured in the Ruby base phantom with MicroDiamond detector connected with Unidose E (PTW). Simultaneously, electronic portal imaging device (EPID) was collecting data for transit dosimetry. Data collected from EPID were calculated in EPIgray (DosiSoft/Elekta), which is used for calculations in transit dosimetry. In EPIgray the finite tissue maximum ratio (fTMR) is used, which is ratio between dose measured in a phantom at depth Dmax (maximum dose) and dose measured in the same conditions but without phantom. Based on this ratio, it is possible to determine dose. Statistical analysis was performed using the Mann-Whitney U test, comparing each method to the TPS.

Figure 1. Percentage dose differences between values from the TPS (zero/reference) and those obtained by measurement in the Ruby phantom and dose calculations in RadCalc and EPIgray software.

Results: Non significant differences between methods were observed. The highest uniformity results were obtained for the measurement in the Ruby phantom using the MicroDiamond detector (p-value 0.946). The RadCalc presented lower doses vs. TPS (p-value 0.079). The lowest uniformity results in the method were observed between TPS and EPIgray (p-value 0.675). Conclusion: For each method results passed the accepted clinical criteria. The most similar results to TPS were obtained for MicroDiamond detector. The measurement and calculation give different type of information about the dosimetric quality of the treatment plan, but they can be used adjunctive.

Keywords: quality assurance, dose calculation

References: 1. Held M, Cheung J, Perez Andujar A, et al. Commissioning and Evaluation of an Electronic Portal Imaging Device Based In-Vivo Dosimetry Software. Cureus 2018; 10(2): e2139.DOI10.7759/cureus2139 2. https://www.dosisoft.com/products/epigray/