Room: AAPM ePoster Library
Purpose: End-to-end testing, E2E, is a necessary process for assessing the readiness of SRS program and annual QA of an SRS system according the AAPM MPPG#9a. This study investigates the differences between using a new SRS MapCHECK, SRSMC, system and an antrhropomorphic phantom film-based system in a large network with different SRS delivery techniques.
Method: Three SRS capable LINACs (Varian Medical Systems, Palo Alto, CA) at three different sites were chosen to represent a hospital network, Trilogy with M120 multi-leaf collimator,MLC, TrueBeam with M120 MLC, and TrueBeam Stx with HD120 MLC. An anthropomorphic STEEV phantom (CIRS, Norfolk, VA) and a phantom/diode array: StereoPhan/SRSMapCheck (Sun Nuclear, Melbourne, FL) were CT scanned at each site. The new STV-PHANTOM EBT-XD films (Ashland, Bridgewater, NJ) were used. SRS cranial plans using dynamic conformal arc and volumetric-modulated arc therapy, with 1-4 targets, were planned with Eclipse v15.5, TPS, using a custom SRS beam model for each machine. The dosimetric and localization accuracy were compared. The time of analyzing of the two systems by three teams of physicists were also compared to assess the throughput efficiency.
Results: film, the dose difference, ΔD, from the three sites were found to be -3.2% to 3.7%. The maximum localization errors, Eˡᵒᶜᵃˡ, were found to be within 0.5mm and 1.0mm for TrueBeam and Trilogy, respectively. With SRSMC, the ΔD were found to be within 5% from the TPS calculation. Eˡᵒᶜᵃˡ were found to be within 0.7 to 1.1 mm for TrueBeam and Trilogy, respectively. Comparing with film, an additional uncertainty of 0.7mm was found with SRSMC. The delivery and analysis time were found to be 6 hours and 2 hours for film and SRSMC, respectively.
The SRS MapCHECK agrees dosimetrically with film within measurement uncertainties. However, film shows superior sub-millimeter localization resolving power for MPPG# 9a application.
Funding Support, Disclosures, and Conflict of Interest: One of the authors has a research grant from Ashland Inc., the manufacturer of GafChromic film