Abstract
Purpose: To present QA measurements over extended periods at our institute and recommend a QA program for image‐guided radiosurgery on Novalis Tx system. Method and Materials: Novalis Tx system is developed based on a Trilogy linear accelerator featuring BrainLAB 6D‐ExacTrac, HD120‐MLC, MV‐EPID and KV‐OBI&CBCT. Utilization of any new technology and equipment necessitates a comprehensive QA program to maintain and monitor system performance characteristics. In this study, we carried out a systematic QA program, including linear accelerator QA, treatment planning QA, planning MRI and CT QA, treatment imaging QA, patient‐specific QA, and system setup procedures for image‐guided radiosurgery. Methodology, frequencies and criteria of QA tests were based on AAPM TG40, TG42, TG51, TG66, and ACR MRI QC. Results: Comprehensive QA was performed from March to December 2008. 1) Daily Winston‐Lutz tests of 199 measurements showed that isocenter of gantry rotation was 0.44±0.21mm; isocenter of couch rotation was 0.34±0.20mm, within 1mm tolerance. Other linear accelerator QA results were within TG40 criteria. 2) Treatment planning QA was conducted with spot‐checks and a RPC SRS head phantom test. In spot‐checks, dosimetric discrepancies were within 3% (3.5% for the 4mm cone). RPC radiosurgery test was passed with less than 1% dosimetric deviation, and 100% geometric match. 3) Daily MRI QA showed that average geometric distortion was −0.2±0.4mm, −0.3±0.4mm, and −0.9±0.1mm along vertical, lateral, and longitudinal directions, within 1mm on phantom, 50% of ACR specifications. 4) OBI QA showed that imaging isocenter displacement was 0.46±0.30mm at AP and 0.76±0.19mm at RLAT. 5) Over ten months, 128 patients with intracranial lesions were treated with radiosurgery. All second MU checks were within 3%, and there were none treatment errors associated with the SRS treatments. Conclusion: Comprehensive QA program for image‐guided radiosurgery has been developed with proper methodology, frequency and criteria on Novalis Tx system, demonstrated with extensive measurements.
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