Purpose: An end-to-end procedure for a new anthropomorphic phantom was developed for MLC-based SRS commissioning on a linear accelerator. This procedure was developed and tested by Northwest Medical Physics Center at three independent clinical sites with Varian Edge and TrueBeam accelerators, following local standards for MLC-based SRS planning.
Methods: The end-to-end procedure uses a novel anthropomorphic SRS phantom recently developed by Varian Medical Systems. This phantom was used to verify isocenter coincidence, targeting accuracy, treatment modulation and absolute dosimtery for dose delivery to a single target and single-isocenter, multitarget geometries. Testing was performed at three clinical sites in an all-Varian environment consisting of ARIA, Eclipse treatment planning, and TrueBeam/Edge machines with Millennium and HD-MLCs. CT simulation and treatment delivery was performed using Qfix Encompass and Brainlab mask systems. Treatment plans were developed for RapidArc and dynamic conformal arcs at 6FFF and 10FFF. Consistent planning criteria was applied across all three clinical sites. A nominal dose of 16 Gy was prescribed for each plan using a sites’ standard beam geometry for SRS cases.
Results: Pinpoint ion chamber readings showed agreement with the planned dose to within 3% for treatment delivery to a 2-cm target. DoseLab software was used to perform relative gamma analysis of the film dose planes compared to extracted data from the treatment planning system. Most single and multitarget treatment plans showed gamma passing rates >90% for 3% and 1 mm after auto-registration shifts ≤ 1 mm in any direction.
Conclusion: Validation of the end-to-end procedure at three independent clinical sites indicates that it is acceptable for the commissioning of MLC-based SRS treatments. Data is now being acquired at additional clinical sites for the purposes of establishing acceptance criteria for end-to-end measurements performed on TrueBeam and Edge machines.
Funding Support, Disclosures, and Conflict of Interest: This work received financial support from Varian Medical Systems.