Daily Based Quality Assurance of Volumetric Modulated Arc Therapy for the Full Session of Treatment

Volumetric modulated arc therapy (VMAT) with highly complex advanced delivering technique, is widely practiced in radiation therapy and requires a quality assurance for treatment plan at least once a treatment session. In this study we collected six VMAT patients with different treatment sites. The VMAT plans and their quality assurance (QA) plans were performed on a daily basis before treatment for their full period of treatment. We tried to evaluate the accuracy of their delivering through analyses of first mechanical error of multileaf collimator (MLC) movement and second dosimetric error of beam delivery. We used a MATLAB program and portal dosimetry to estimate a maximum root mean square (RMS) error from dynalog files for mechanical analysis and a gamma index from portal dosimetry for dosimetric analysis, respectively. We introduced newly in this study a representative VMAT QA to be used to perform a routine VMAT QA. The daily variation of maximum error RMSs for all treatment sites were all below maximum 0.3503 ± 0.0002 mm for treatment plans and QA plans and they all showed the gamma pass rate of more than 98%. Mean of inter difference between treatment and QA plans stayed below 0.04 mm, showing that QA deliveries agree well with treatment deliveries. The Linac used kept a good performance within the tolerances in American Association of Physicists in Medicine (AAPM) TG142 guideline for the period of research. We suggest that the representative VMAT QA can be a good surrogate for real VMAT plan and “whole time” plan QA for a patient selected randomly at least once a year be performed to confirm the long-term stability of Linac performance.