(Saturday, 4/4/2020) [Mountain Time (GMT-6)]
Purpose: This study is to validate the dose profiles and RapidArc Treatment planning model for SRS-SBRT in the commissioning of the Varian Edge ™ System using a full frameless EET StereoPHAN and Gafchromic EBT3 Radiochromic Films.
Methods: Per protocols in TG55, TG 42 and MPPG 9a, we validated a full EET in the commissioning of the Varian Edge Radiosurgery System. EBT3 films were chosen because they have a high spatial resolution, weak energy and dose rate dependence, water-resistant with near tissue equivalence. EBT3 Films were inserted and positioned inside the head of the E2E stereoPHAN phantom on the treatment Couch. RapidArc treatment phantom plans for multiple energies (6 FFF, 6, 10 FFF, 10MV photon beams), single target and multitarget were developed with the Varian’s Eclipse planning system and delivered to the film in a single arc and multi-arc. After 24 hours, the exposed films were scanned in a 48-bit RGB transmission mode on an Epson 11000XL expression scanner and analyzed using triple-channel dosimetry and the FilmQAPro Pro software.
Results: The positioning and dose distributions were validated using the gamma test criteria with a 3% relative dose per 1 mm (10 % threshold) between the film measured dosed and calculated dose distributions. The 1 target 6 multi-arc and 1 target 10 multiarc plans passed the gamma criteria test with at least a 97.0 % and NAT index (3% local difference and 1 mm criteria) of at least 9.3 while the 1 target 6F plan had a gamma pass rate of 97.2 % with NAT index of 10.9, and the 1 target 10F plan with a gamma of 98.8 % and NAT index of 5.9.
Conclusion: EBT3 small field dosimetry Films validation measurements showed an excellent agreement of the beam models by the TPS with measured dose distributions.
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