A COMPARISON OF THREE DOSIMETRIC PATIENT QUALITY ASSURANCE TOOLS FOR PRECISION RADIOTHERAPY OF HEAD AND NECK CANCER

Abstract

Precise and very complex radiotherapy technique Volumetric Modulated Arc Therapy (VMAT) provides uniform and conform dose distribution. Despite that, there is still a possibility that due to precision in the dose calculation of the treatment planning system (TPS) or the errors associated with it, there can be distinctions between dose distributions which are planned and delivered. The gamma index (GI) is the parameter by which is quantified the difference between these dose distributions and this index may depend on the pathology and the area to be treated. The goal of this work is to estimate different parameters of the gamma index (GI) for head and neck cancer treatments. The analysis was based 2%/2 mm, 3%/3 mm criteria. 10 treatment plans were created with the VMAT technique calculated with the TPS Eclipse V.15.6 (Varian Medical Systems, Palo Alto, CA) and measured with the Dolphin (IBA dosimetry, GmbH, Germany), PTW Octavius 4D 1500 (PTW-Freiburg, Freiburg, Germany) and Varian aS1200 electronic portal imaging device-EPID (Varian Medical Systems, Palo Alto, CA) were analyzed. A Varian VitalBeam, linear accelerator with a 6 MV photon beam was used to deliver the dose. The obtained results of the analysis were that a gamma passing rate (%GP) greater than 90% for 2%/2 mm and greater than 95% for 3%/3 mm analysis criteria. The criteria for gamma analysis can be less strict and then the %GP can increase. A significant difference was also observed when the PTV has a greater volume.