Automated Linac QA Using Scripting and Varian Developer Mode

Abstract

Purpose: Linac quality assurance (QA) can be time consuming involving set up, execution, analysis and subject to user variability. The purpose of this study is to develop qualitative automation tools for mechanical and imaging QA to improve efficiency, consistency, and accuracy. Methods and Materials: Traditionally QA has been performed with graph paper, film, and multiple phantoms. Analysis consists of ruler and vendor provided software. We have developed a single four-phantom method for QA procedures including light-radiation coincidence, imaging quality, table motion and Isocentricity and separately cone beam computed tomography. XML scripts were developed to execute a series of tasks using Varian’s Truebeam Developer Mode. Non-phantom QA procedures have also been developed including field size, dose rate, MLC position, MLC and gantry speed, star shot, Winston-Lutz and Half Beam Block. All analysis is performed using inhouse MATLAB codes. Results: Overall time savings were 2.2 hours per Linac per month. Consistency improvements (standard deviation, STD) were observed for some tests. For example: field size improved from 0.11 mm to 0.04 mm and table motion improved from 0.17 mm to 0.12 mm. CBCT STD improved from 0.99 mm to 0.61 mm for slice thickness. No STD change was observed for Isocentricity test. We noticed an increase in STD from 0.33 mm to 0.41 mm for light-radiation coincidence test. There was a small drop in field size accuracy. Isocentricity showed an increase in measurement accuracy from 0.47 mm to 0.15 mm. Table motion increased in accuracy from 0.20 mm to 0.16 mm. Conclusion: Automation is a viable, accurate and efficient option for monthly and annual QA.