SU‐E‐T‐264: CTRC Experience: Patient Specific IMRT Quality Assurance with Ionization Chamber and Detector Arrays

Abstract

Purpose: This study was conducted to review the IMRT QA results of patient plans (grouped by anatomical site, MLC type, and TPS) delivered at the Cancer Therapy and Research Center using Varian LINACs and Hi Art Tomotherapy units. Methods: The patient data was evaluated for the time period 2006–2011 and it involved several methods used in the QA process. Ion chambers and film were used in the earlier years followed by ion chamber arrays in the latter years. The patients were grouped according to several parameters including site of treatment, type of machine, and magnitude of the differences between measured and planned data. From 2006 until 2009, 736 tomotherapy plans, 817 Pinnacle3 plans, and 351 Corvus plans were evaluated using ion chambers and film. The pass criterion at the institution at the time of these measurements was 3% dose difference and 3mm distance agreement. For the period 2009–2011, 1466 patient IMRT QAs were performed on Varian linacs, which were equipped with Millennium 80, 120 and High‐Definition 120 multileaf collimators and they were evaluated according to pass criteria of the institution (gamma = 90%). Results: The average gamma values of the brain, head and neck, thorax, abdomen, and pelvis cancer cases were 97.2%, 95.7%, 96.2%, 97.0%, and 96.2%, respectively. The average gamma values based on the 80, 120, HD 120 and Tomo MLC configurations were 96.5%, 96.2%, 96.3%, and 97.0%, respectively. The average differences between the measured and calculated plans for the Pinnacle3, Hi‐ART TomoTherapy, and Corvus treatment planning systems were 2.3%, 0.004%, and 0.02%, respectively. Conclusion: Based on the anatomical site, head and neck cancers had the lowest gamma value for the patients treated and the brain cancers had the highest gamma value. The TomoTherapy machines had the best overall gamma values as compared to the CLINAC machines.