Comparison of PDIP and glaas algorithms used in quality control with portal dosimetry of intensity modulated radiotherapy plans

SUMMARYIn radiation treatment, delivering the desired dose to the target volume accurately has a great importance. In complex treatments such as intensity modulated radiation therapy (IMRT) and intensity modulated arc therapy (IMAT) dosimetric quality control (QC) is required. The quality control is done by analysing of similarity between dose distribution modelled in treatment planning system (TPS) and measured dose distribution. Portal dosimetry is a quality control technique done with electronic portal imaging device (EPID). In this study, we aimed to compare the QC of IMRTand IMAT treatment plans done in Eclipse (version 10) TPS with portal dosimetry performed by Varian Portal Dosimetry software using PDIP algorithm and Epidose Epiqa software using GLAaS algorithm. Following the optimization process, dose distribution of 40 plans (head and neck, brain, prostate) done by inverse planning technique is calculated by Anisotropic Analytical Algorithm (AAA), and quality control plans are created. The plans are measured by aS1000 EPID integrated into Varian Trilogy linear accelerator and the dose distribution images are obtained.Subsequently gamma analysis is performed in the criteria of 3 mm distance to agreement and 3% dose difference with Portal Dosimetry and Epiqa softwares, and the algorithms were compared. The mean values of differences between softwares were 2,5% in IMRT, 1,3% in IMAT. According to gamma analysis done with calculated and measured dose distribution images, softwares were statistically different for all plans (Epiqa 99,4 ± 1,0, Portal Dosimetry 97,6 ± 2,4, p<0,001) and head-and-neck plans (Epiqa 99,3 ± 0,9, Portal Dosimetry 98 ± 2,0, p<0,001). Theresults of Epiqa were proximate to ideal when compared for all plans. In all plans the difference between mean values of both algorithms are 2%. Both techniques are acceptable for quality control of intensity modulated treatment planning.Key Words: Gamma analysis, GLAaS, PDIP, IMRT, VMAT