SBRT/SRS treatment, related to Brain, Lung and Nodes, were calculated using the AcurosXB 13.6.23 algorithm and TPS Eclipse Varian Medical Systems (13.6), VMAT and Flattening Filter Free (FFF) mode (6X-FFF and 10X-FFF beams). GafchromicTM EBT3 calibration was obtained using 6X-FFF and 10X-FFF photon beams and VARIAN TRUE BEAM 2.5 (0-25 Gy); they were digitized with EPSON EXPRESSION 10000 XL, one scan method, transmission mode and analyzed with FILMQA software using triple channel method. To avoid scan-to-scan variability and uncertainty, EBT3 films, exposed to each VMAT arc, were digitized in a single scan with two reference films: a film exposed to 80% dose max of the calculated dose frequency distribution and an unexposed film. To obtain a linear dose scaling using the calibration curve and a more accurate dose map, each film was associated to a calibration curve created using 0 Gy, 20% and 40% of calculated max dose and finally the reference film (80% of calculated max dose). The agreement between calculated and measured dose distributions were evaluated in terms of ɣ passing rate. Criteria were: 3%3mm, 2%2mm, 2%1.5mm, 1.5%1.5mm, 3%1.5mm. Results obtained were then compared with the pre-treatment verification procedures normally used: EPID and EPIQA software.
Fig. 1: mean values and relative errors of the ɣ passing rate, for each criteria, obtained both with the EPID-EPIQA and GAF-FILMQA method.
Fig. 2: results obtained, by relating the modulation coefficient and the ɣ passing rate (criteria 3%1.5mm), with the two verification methods.