Comparison of gamma analysis with using different dosimetric systems for pre-treatment verification of intensity-modulated radiation therapy

Abstract

The evaluation of the agreement between calculated and measured dose plays an essential role in the quality assurance procedures of intensity-modulated radiation therapy (IMRT). This study aimed to compare gamma analysis using portal dosimetry (PD), Epiqa, and 2D array detector for dose verification of radiotherapy treatment plans. Five field step-and-shoot IMRT plan was performed for 20 prostate IMRT patients using the dual-energy DHX linear accelerator (Varian Medical System, Palo Alto, Calif., USA). The treatment plans were created using Varian DHX Eclipse treatment planning system (TPS) version 15.1. All measurements were performed by aS500 EPID integrated into Varian DHX linear accelerator and 2D array detector. The dose distribution was evaluated with gamma area histograms (GAHs) generated using different γ criteria (1%/1 mm, 2%/2 mm, 3%/2 mm, and 3%/3 mm) for dose agreement and distance to agreement parameters. Statistical analyses were evaluated by using Mann–Whitney U test and Kruskal–Wallis test, and p-value of p < 0.01 was considered to be significant. The average pass rate for 20 IMRT plans was above 95 for all devices with 2%/2 mm, 3%/2 mm, and 3%/3 mm. The mean and standard deviation pass rates (γ ≤ 1) were found to be 99.80 ± 0.19, 99.35 ± 0.34, and 97.53 ± 0.71 for PD, Epiqa, and 2D array, respectively. All IMRT plans passed 2%/2 mm, 3%/2 mm, and 3%/3 mm gamma by more than 95 of three dosimetric systems. They are all in good agreement with the literature. All three devices are acceptable for quality control of IMRT. Due to the simplicity and fast evaluation process, PD can be preferred for quality control.