Gamma Index Analysis as a Patient-Specific Quality Assurance Tool for High-Precision Radiotherapy: A Clinical Perspective of Single Institute Experience

PurposePatient-specific quality assurance (QA) by gamma (gamma) analysis is an important component of high-precision radiotherapy. It is important to standardize institute-specific protocol. In this study, we describe our institutional experience of patient-specific QA for high-precision radiotherapy from a clinical perspective.MethodsThe planning data of 56 patients treated with intensity-modulated radiotherapy (IMRT)/volumetric modulated arc therapy (VMAT) were included. gamma index analysis was done using Octavius 4D IMRT QA phantom (PTW, Freiburg, Germany) using 3 mm/3% criteria. Local, global, and volumetric gammas were calculated and compared. The relationship of gamma index in the transverse, coronal, and sagittal direction and anatomical region of treatment was explored.ResultsGlobal three-dimensional (3D) gamma indices in the coronal, sagittal, and transverse axes were 96.73 +/- 2.35, 95.66 +/- 3.01, and 93.36 +/- 4.87 (p < 0.05). The average local two-dimensional (2D) gamma index was 78.23 +/- 5.44 and the global gamma index was 92.41 +/- 2.41 (p < 0.005). The average local 3D gamma index was 84.99 +/- 4.24 and the global 3D gamma index was 95.25 +/- 1.72 (p < 0.005, paired t-test). The average local volumetric gamma index was 84.29 +/- 4.73 and the global volumetric gamma index was 95.96 +/- 2.08 (p < 0.005). 3D global gamma index was significantly different in different anatomical regions (p < 0.05).ConclusionOur study shows that gamma index analysis is a useful parameter for routine clinical IMRT QA. The choice of type of gamma index depends on the context of use and degree of stringency in measurement. Average 2D and 3D global gamma were different in anatomical regions. The average 3D gamma index was significantly different in axes. No difference was observed with techniques of IMRT/VMAT. Localization of failed points in CT anatomy can be advantageous for clinical decision-making.