Correlation analysis between 2D and 3D patient-specific quality assurance for volumetric modulated arc therapy

Background: Aim is to find correlation between 2D-gamma passing rate and 3D-DVHbased pre-treatment patient-specific quality assurance. Materials and Methods: 21 head and neck and 21 pelvis patients, treated with volumetric modulated arc therapy (VMAT) were selected for this study. All patients were planned with Elekta VersaHD linear accelerator using Monaco (5.11) treatment planning system. 2D-planar dose measurements were performed with IBA-I'matriXX evolution detector-array using MyQA-Patients software. For 2D-Gamma index evaluation, 3%/3mm and 2%/2mm criteria were used. 3D-dose measurements were performed using the IBA-COMPASS system. For 3D measurement, Monaco and COMPASS doses were compared in terms of percentage dose differences to PTV and organs at risk. For PTV D95, D2, and D50 (dose received by 95%, 2%, and 50% volume), similarly for OARs D2 and D50 were noted. 3D Gamma index was also noted. Correlation coefficient and its corresponding two-tailed p-value (<= 0.05, for statistically significant) were calculated for 2D-gamma passing rate and 3D Gamma index & percentage dose differences of 3D-DVH based metrics (Monaco calculated versus COMPASS measured). Strength of correlation will be considered weak or strong based on the r -value. Results: 2D-Gamma index passing rate was 98.6 +/- 1.8%, 92.1 +/- 7.1% and 98.5 +/- 1.3%, 93.5 +/- 4.4% for head-neck and pelvis patients (3%/3mm, 2%/2mm criteria) respectively. Percentage dose-differences for PTV D95, D2, D50 for head-neck and pelvis were: 4.22 +/- 2.09%, 4.25 +/- 2.23%, 3.93 +/- 1.59 & 0.60 +/- 1.96%, 1.53 +/- 1.64%, 1.59 +/- 1.20% respectively. Spine and brainstem D2 were 0.84 +/- 6.10%, 0.77 +/- 2.70%, bladder and rectum D50 were 3.75 +/- 3.31%, -2.19 +/- 3.60%. Conclusion: No strong correlation was observed between the 2D Gamma passing rate and 3D measurements.