On using 3D γ-analysis for IMRT and VMAT pretreatment plan QA

Purpose: To investigate using 3D γ analysis for IMRT and VMAT QA. Methods: We explored and studied 3D γ-analysis by comparing TPS computed and EPID back-projection reconstructeddoses in patient’s CTimages. Two 3D γ quantities, γPTV and γ10, were proposed and studied for evaluating the QA results, and compared to 2D γ (MapCheck composite: γMC). Results: It was found that when 3%(global)/3 mm criteria was used, all IMRT and 90% of VMAT plans passed QA with a γ pass rate ≥90%. A significant statistical correlation was observed between 3D and 2D γ-analysis results for IMRT QA if γ10 and γMC are concerned, but no significant relation is found between γPTV and γMC. Conclusions: 3D γ analysis based on EPIDdose back-projection may provide a feasible tool for IMRT and VMAT pretreatment plan QA.