(Saturday, 4/7/2018) 10:30 AM - 12:30 PM
Room: Marquis Ballroom 5-8
Purpose: To verify the representative data for Varian SRS cone output factors (OF) for a TrueBeam linear accelerator utilizing two common SRS diode detectors and Gafchromicâ„¢ film.
Methods: The Sun Nuclear EDGE detector, PTW 60012 stereotactic diode, and Gafchromicâ„¢ EBT3 film were used to measure the OF for Varian TrueBeam SRS cones. Measurements were taken for 6MV and 6FFF energies in a solid water phantom (EDGE and EBT3) and Sun Nuclear 1D water tank (EDGE and PTW) at 5cm depth and 95cm SSD. Cone diameters ranged from 4mm to 17.5mm. Measurements were also made for field sizes of 5x5cm and 10x10cm with the EDGE detector, PTW 60012 diode, EBT3 film, and Exradin A12 Ion chamber for daisy chain method comparison.
Results: The EDGE showed a maximum difference with the representative data of -1.64% for 6MV and -1.27% for 6FFF. The PTW show a maximum difference of -3.15% for 6MV and -3.35% for 6FFF. The OF measured by the EBT3 film showed maximum differences with the representative data of -8.21% for 6MV and -9.1% for 6FFF. Comparison of OF with and without the daisy chain correction demonstrated a maximum variation of 0.5% and 0.9% for 6MV and 6FFF for the two chambers.
Conclusion: Varian representative data showed agreement with the EDGE detector and PTW 60012 stereotactic diode, but showed a comparatively large difference with the EBT3 film at the smallest cones. The daisy chain correction had no significant effect on the measurements for either diode due to their ability to measure the 10x10cm reference field. The large difference between EBT3 film and diode measurements may be explained by the environmental dependencies of the diodes and the inherent uncertainty in the scanning and analysis of the film.
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