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

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) are advanced radiotherapy techniques requiring rigorous quality assurance (QA).
• Traditional 2D QA methods may not fully capture dose distribution complexities in 3D space.
• Epidermal electronic portal imaging devices (EPIDs) offer potential for dose reconstruction and 3D QA.

Purpose of the Study:

• To investigate the utility of 3D gamma analysis for pretreatment QA of IMRT and VMAT plans.
• To compare 3D gamma analysis metrics with conventional 2D QA results.

Main Methods:

• Explored 3D gamma analysis by comparing treatment planning system (TPS) computed doses with EPID back-projection reconstructed doses.
• Proposed and evaluated two 3D gamma metrics: gamma(PTV) and gamma(10).
• Compared 3D gamma analysis results against 2D gamma analysis using a MapCheck composite (gamma(MC)).

Main Results:

• Using a 3% global/3 mm criterion, 100% of IMRT and 90% of VMAT plans achieved a gamma pass rate of ≥90%.
• A significant statistical correlation was found between 3D gamma(10) and 2D gamma(MC) for IMRT QA.
• No significant correlation was observed between 3D gamma(PTV) and 2D gamma(MC).

Conclusions:

• 3D gamma analysis, utilizing EPID dose back-projection, presents a feasible approach for IMRT and VMAT pretreatment plan QA.
• The gamma(10) metric shows promise for correlating 3D dose evaluation with 2D QA results in IMRT.
• Further investigation may refine the application of 3D gamma analysis for comprehensive radiotherapy QA.