Room: Exhibit Hall
Purpose: To present a comparison of the absolute dosimetry response of Gafchromic EBT3 and EBT-XD films for film QA of patient-delivered VMAT stereotactic radiosurgery plans.
Methods: Absolute dosimetry of both Gafchromic EBT3 and EBT-XD films were investigated in eight patient stereotactic radiosurgery treatment plans. Two-dimensional dose planes were calculated (Varian Eclipse TPS v13.6). Treatments used an Elekta Agility linac with an mlc-based VMAT technique and 6 MV beam energy. All volumes were prescribed to 2,000 cGy covering at least 98% of treatment volumes. The films were irradiated using a Standard Imaging Lucy phantom with film insert. Film analysis was performed using RIT V6.6.32 with a red channel VIDAR Dosimetry Pro Advantage film digitizer. A calibration curve was created for each film type under standard conditions and used for absolute dose analysis. Film dose planes were compared to calculated 2D dose planes using gamma analysis with various gamma-pass criteria.
Results: Pass rates for gamma analysis using a variety of gamma-pass criteria are as follows. Average pass rates for EBT3 were 97.9% (5%, 2mm), 96.5% (3%, 2mm) and 93.0% (2%, 2mm) with standard deviations 1.7%, 2.0% and 2.3%, respectively. Average pass rates for EBT-XD were 97.0% (5%, 2mm), 95.5% (3%, 2mm) and 91.9% (2%, 2mm) with standard deviations of 3.1%, 3.4% and 3.8%, respectively. The EBT3 showed equivalent agreement to the EBT-XD between calculated and measured results.
Conclusion: Gafchromic EBT-XD film was recently developed in 2015 and has shown an improved calibration curve gradient at high dose regions typical of stereotactic radiotherapy. Our study demonstrated equivalent gamma-pass percentages with EBT3 film for the eight patient treatment plans, despite this calibration curve difference. Clinically, for stereotactic radiosurgery dose verification, EBT3 film may be just as suitable as EBT-XD.