Portal Dosimetry as a patient specific Quality Assurance tool for Volumetric Arc Radiotherapy

Abstract

Introduction: Volumetric Arc Radiotherapy (VMAT) is an advanced technique. Calculations of VMATplans are not so accurate even with State-of-Art dose calculation algorithms due to their complexity.Hence pre-treatment patient specific Quality Assurance (QA) of each VMAT plan is required. In thepresent study Electronic Portal Imaging Device (EPID) based portal dosimetry system was used forpre-treatment patient specific QA. Material and Methods: A total of 50 patients were chosen inthis study. Verification plans of each patient were calculated for portal dosimetry then executed onthe EPID system to measure the spatial distribution of radiation dose. Calculated and measured dosedistribution were compared to evaluate Gamma Index (GI) passing criteria of Dose Difference (DD)of 3% and Distance–to-Agreement (DTA) of 3mm, Area Gamma (γ% ≤1) >95%, Average Gamma(gAve) <0.5% and Maximum Gamma (gMax) <3.5%. Results: The mean values of Area Gamma (γ%≤1) were observed to be varied from 99.14±0.23% to 99.87±0.18%. The Mean Values of AverageGamma (gAve) are found to vary from 0.19±0.05% to 0.15±0.04% and the mean values ofMaximum Gamma (gMax) found to be varied from 1.94±0.37% to 1.59±0.41%. All the plans werepassed the gamma index criteria with very good agreement. Thus the use of Portal Dosimetry forpre-treatment patient QA is found to be a very useful, quick, precise, efficient and effective pre-treatment patient specific QA tool for VMAT treatment. Conclusion: Portal Dosimetry can be utilizedfor routine use for patient specific quality assurance for Volumetric Arc Radiotherapy treatment.