Commissioning of Clinac IX Trilogy Linear Accelerator for Stereotactic Radiosurgery

Abstract

Comprehensive quality assurance (QA) and beam data acquisition has been performed for commissioning of Varian Trilogy linear accelerator for stereotactic radiosurgery (SRS). Mechanical, electrical and radiological tests were performed to check linac performance as per American Association of Physicists in Medicine (AAPM) Task Group (TG) 142. The geometric isocentre accuracy, congruence check and calibration of kV and MV imager were performed using the Isocal QA device. The off axis ratio profiles, depth dose data and beam output factors of 6 MV SRS beam for the field sizes ranging from 2 2 cm2 to 15 15 cm2 were measured using SFD diode detector and cc13 semiflex ion chamber. The multileaf collimator (MLC) characterization was done in the treatment planning system (TPS) using the parameters measured with the CC13 semiflex ionisation chamber in water phantom. Dose measured with 2D ion chamber array was compared to that calculated in TPS. The maximum change in MV and kV imager isocentre was within 0.03 cm. The variation between SFD measured and ion chamber measured beam data is in positive correlation for fields sizes down up to 2 2 cm2. Variation in output factors is 0.56 0.05 %. The measured beam data is imported and calculated in the Eclipse TPS and is found within 1% gamma agreement index (GAI) with the Analytical Anisotropic Algorithm (AAA) model data. GAI for TPS verification QA is 97.8%, 98.5% and 98.3% respectively for fix jaw 2 2 cm2, 5 5 cm2 and rapid arc SRS plan. Successful modelling of the photon beam for high dose rate SRS mode is achieved for clinical treatment of patients.