Implementation of TG-218 for patient-specific quality assurance tolerance and action limits determination: Gamma passing rate evaluation using 3DVH software.

Purpose: To determine the tolerance limit (TL) and action limit (AL) of gamma passing rates (%GP) for volumetric-modulated arc therapy (VMAT) patient-specific quality assurance (PSQA) according to the American Association of Physicists in Medicine (AAPM) Task Group (TG)-218 recommendations, and to comparatively evaluate the clinical relevance of 2D %GP and 3D %GP.

Methods: PSQA was performed for 100 head and neck (H&N) and 73 prostate cancer VMAT treatment plans. Measurements were acquired using a cylindrical water equivalent phantom, hollow in the center, allowing measurements with homogeneous or heterogeneous inserts.