SU-E-T-155: Evaluating IMRT and Volumetric Arc Therapy Patient-Specific Quality Assurance by Using Octavius 4D System

Abstract

Purpose: The goal of this study was to perform and evaluate pre-treatment patient specific verifications of IMRT and volumetric arc therapy(VMAT) plans by using a new, commercially available 2D array Octavius 4D system. Methods: The OCTAVIUS 4D system and its accompanying software (VERISOFT) by PTW were evaluated for the accuracy of the dose reconstruction for patient specific QA. (1)Commissioning of Octavius 4D system for IMRT and VMAT technique was by following the tests suggested in the AAPM TG119 protocol, in order to give a benchmark for optimization process and the calculation accuracy. (2) Verification of total 87 clinical IMRT and VMAT plans, 50 IMRT and 37 VMAT plans were used for the comparison. Comparing treatment planning system calculated versus measured dose using local gamma index analysis (3%, 3 mm criteria). Results: (1)Agreement between calculated and planar doses measured by using Octavius 4D system. It was very good for both modalities. (2)Verifications of pre-treatment clinical plans, showed an average gamma evaluation passing ratio of 97.3±1.9% for 50 IMRT cases and an average pass ratio of 94.94±2.43% for 37 VMAT cases. 2D gamma evaluation for IMRT plans showed 96.82%, 97.5%, 97.93% and 96.94% passing results for head and neck, chest, abdomen and Pelvis sites. Volumetric global gamma evaluation for VMAT plans showed 93.8%, 94.66% and 96.27% passing results for chest, abdomen and Pelvis sites respectively. Conclusion: The TG119 results suggest that it is appropriate to apply patient-specific QA action levels derived from IMRT to VMAT technique. Octavius 4D system together with 2D array 729 is an appropriate and efficient tool for IMRT and VMAT patient specific QA and can potentially improve the data collection and analysis. Further studies will focus on more complex VMAT plans (head and neck treatment plans).