(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To develop and validate a portal dosimetry algorithm for 6FFF on the digital megavoltage imager (DMI) of Varian’s VitalBeam accelerator system.
Methods: The Eclipse TPS v15.5 now includes a portal dosimetry (PD) calculation model (AAA_15511) for 6FFF. Unlike the analytical anisotropic algorithm (AAA) for patient dose calculations, the AAA portal dose model uses scatter kernels calculated in the imager scintillation material to predict the appropriate dose response. This is done using the 6FFF commissioned beam data. All that is required is the source to imager distance (SID) for imager calibration, and the MU used to deliver 1 CU at the central axis. The imager was calibrated for 1CU=100cGy with delivery of 100MU at SID=100cm for 6FFF. Verification plans provided with the pre-configured PD package were used to verify the AAA PD model.
Results: The Gamma criteria used is 3%-3mm with 10% threshold. Gamma analysis of the DynChair and AIDA fields was 96.3% and 100% passing. The maximum average dose difference (MADD) was 0.03CU. Gamma analysis of all open fields (3.0 cm2 to 30 cm x 30 cm) was 100% passing with a MADD of 0.07CU. Gamma analysis of the IMRT fields ranged from 100% to 96.4% with a MADD of 0.01CU. Gamma analysis of the Rapid Arc fields showed 100% passing with a MADD of 0.02CU. Additional open fields of 1.0 cm2 and 2.0 cm2 defined by MLC with a jaw setting 3.0 cm2 were analyzed using criteria of 2%-2mm and MCL CIAO+5mm. Gamma results were 98.3% and 100% respectively with a MADD of 0.03CU.
Conclusion: Validation results indicate the use of AAA modeling for PD of 6FFF on the DMI electronic portal imager is acceptable for clinical use. In addition, its use for stereotactic treatment QA was also demonstrated to be acceptable.
Keywords
Not Applicable / None Entered.
Taxonomy
Not Applicable / None Entered.
Contact Email
