A Systematic Approach to Patient Specific QA For Volumetric Modulated Arc Therapy (VMAT)

Abstract

We developed the first non-commercial treatment planning system for volumetric modulated radiation therapy (VMAT) in the United States. Because VMAT involves multiparameter modulations, it is imperative to develop a comprehensive, rigorous and yet, practical procedure for routine patient-specific quality assurance (QA). In this paper, we present our own approach as being currently implemented in our institution. Our patient-specific QA procedure involves multi-levels: pre-treatment QA, on-treatment QA, and posttreatment QA. The pre-treatment QA focuses on dosimetry verification. It is done with the commercial MapCHECK in MapPHAN mounted on an isocentric mounting fixture (IMF). This method is also referred to as the fixed-gantry technique, i.e., the beams always remain perpendicular to the detector plane. The on-treatment QA involves in-vivo optically stimulated luminescent dosimetry (OSLD). Prior to the treatment, two nanoDot ^TM OSLD dosimeters are placed on the patient abdomen under 1 cm bolus at the isocenter location. The irradiated dosimeters are then read by a nanoDot^TM reader and the average reading of the two is calculated. The post-treatment QA involves the analysis of the DynaLog and DLog files. The DynaLog is a treatment log file that contains the planned and actual leaf positions at a given gantry angle. The DLog is a treatment log file that contains the planned segmented treatment table (STT) and the corresponding segment boundary samples, i.e., the actual delivered MU and gantry angle increment at each control point.