Document Type : Original Paper
DEPARTMENT OF PHYSICS, INVERTIS UNIVERSITY, BAREILLY, UP, INDIA
RADIATION ONCOLOGY, SHRI RAM MURTI SMARAK INSTITUTE OF MEDICAL SCIENCES, BHOJIPURA, BAREILLY 243202
Dean, Faculty of Science Invertis University Bareilly-243 123 (U.P.) India
Introduction: The aim is to compare Patient Specific Quality Assurance (PSQA) of 6 MV and 10 MV Volume Modulated Arc Therapy (VMAT) plans performed with Electronic Portal Imaging Device (EPID) at Isocenter using an Improved Gamma Evaluation algorithm.
Materials and Methods: Previously treated patients with 6 MV IMRT for Pelvic cancers were planned, on Eclipse TPS, with 6 MV and 10 MV photon beams using VMAT technology. The PSQA was performed using EPID kept at Isocenter that is 100cm (Source to Imager distance (SID)) and dose verification was done with Improved Gamma Evaluation Algorithm as provided in Portal Dosimetry and investigated the effect on Area Gamma, Maximum Gamma & Average Gamma.
Results: The mean Area Gamma passing rate (%GP±Standard Deviation σ) for 6 MV was 97.06±3.70, 95.42±5.31, 90.93±7.29, 86.55±9.10 and for 10 MV 97.14±6.08, 95.8±8.47, 94.62±9.45, 91.97±13.50 using the criteria 3%/3 mm, 3%/2 mm, 2%/3 mm, 2%/2 mm respectively. There was difference of -0.08%, -0.38%, -3.69%, -5.42% between mean Area Gamma of 6 MV and 10 MV in dose verification. Similarly, for mean Maximum Gamma value for 6 MV was 2.50±0.89, 2.72±0.94, 3.32±1.13, 3.56±1.02 and for 10 MV 2.17±0.62, 2.42±0.72, 2.84±0.90, 3.26±0.94 respectively. For mean average gamma value for 6 MV was 0.36±0.09, 0.42±0.10, 0.45±0.12, 0.53±0.13 and for 10 MV was 0.27±0.16, 0.32±0.19, 0.34±0.20, 0.41±0.24.
Conclusion: There is a marked difference between Area Gamma Passing Rate of 6 MV and 10 MV photon beam. The gamma criteria of 3%/2 mm with 5% Threshold limit and 95% Area Gamma Passing Rate can be used for PSQA using EPID at Isocenter for 6 MV as well as for 10 MV photon beam. There is no marked significant difference in values of mean Maximum Gamma and mean Average Gamma for 6 MV and 10 MV photon beam PSQA.