An algorithm to calculate a collapsed arc dose matrix in volumetric modulated arc therapy

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Radiation Oncology

Background:

• Volumetric modulated arc therapy (VMAT) delivery is complex, requiring robust verification methods.
• Current verification techniques for VMAT may not fully capture delivery intricacies.

Purpose of the Study:

• To present the feasibility of routine VMAT delivery verification.
• To validate an in-house developed algorithm for calculating VMAT dose matrices.

Main Methods:

• VMAT plans were generated using Pinnacle treatment planning system (TPS) for a 6 MV photon beam.
• An in-house algorithm calculated dose matrices, validated against standard patterns and clinical VMAT plans using a 2D ion chamber array and ArcCHECK.
• Gamma analysis with 3%/3 mm criteria was used for dose matrix comparison.

Main Results:

• The algorithm showed excellent agreement with standard patterns (mean γ pass rate 97.7%).
• Clinical VMAT plans demonstrated good agreement between predicted and measured dose matrices (mean γ pass rate 97.6%).
• ArcCHECK validation yielded a mean pass rate of 95.6%.

Conclusions:

• The developed algorithm accurately predicts VMAT dose matrices, considering all leaf trajectories.
• This enables reliable verification of VMAT delivery using a gantry-mounted 2D array detector.