Gamma Passing Rate – Correlation with Patient Specific Quality Assurance Devices using Two Photon energies in Pelvic IMRT

Abstract

The effect on Gamma Passing Rate is studied by changing the Photon Energy in the Patient Specific Quality Assurancein Pelvic IMRT using EPID and MatriXX keeping PSQA device at Isocenter. Dose verification of 62 patients, sufferingfrom pelvic malignancies and treated with Intensity modulated radiation therapy (IMRT), with EPID and MatriXX usinggamma criteria of 3%/3 mm, 3%/2 mm, 2%/3 mm, 2%/2 mm and investigated the effect on Gamma Passing Rate (%GP) bychanging beam energy from 6 MV to 10 MV. The results demonstrated that the behavior of gamma passing rate decreases ascriteria is changed from 3%/3 mm to strict criteria. The mean gamma passing rate for 6 MV beam were (%GP±StandardDeviation σ) 99.64±0.81, 99.45±1.08, 97.57±2.12, 96.17±2.63 using the criteria 3%/3 mm, 3%/2 mm, 2%/3 mm, 2%/2 mmrespectively in EPID. For MatriXX, the mean %GP were 96.69±4.11, 93.85±5.31, 88.17±10.63, 82.2±12.28 respectively.For 10 MV, the mean (%GP±Std. Dev) were 99.64±0.81, 99.45±1.08, 97.57±2.12, 96.17±2.63 for in EPID, 96.69±4.11,93.85±5.31, 88.17±10.63, 82.2±12.28 for MatriXX respectively. Difference between %GP for 6 MV and 10 MV beam were-0.01, -0.11, 1.08, 1.61 with gamma criteria of 3%/3 mm, 3%/2 mm, 2%/3 mm, 2%/2 in EPID. For MatriXX, differencebetween %GP for 6 MV and 10 MV beam were -0.40, -0.24, 0.96, 1.62 respectively. It can be concluded that applying morestrict gamma criteria results in low gamma passing rate. There is marked difference in Gamma Passing Rate (%GP) withchange in photon energy.