Quantified VMAT plan complexity in relation to measurement-based quality assurance results

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Quality Assurance

Background:

• Highly modulated volumetric-modulated arc therapy (VMAT) plans can lead to discrepancies between planned and measured dose distributions.
• Accurate dose verification is crucial for patient safety in VMAT delivery.

Purpose of the Study:

• To evaluate established VMAT complexity metrics for predicting phantom-based measurement results.
• To identify metrics capable of identifying complex VMAT plans that may require additional verification.

Main Methods:

• Investigated 93 VMAT treatments on a TrueBeam linac and 91 on TrueBeam STx linacs.
• Assessed correlations between VMAT complexity metrics and gamma passing rates.
• Utilized Receiver Operating Characteristic (ROC) analysis to determine predictive thresholds.

Main Results:

• Most VMAT complexity metrics showed weak correlations with gamma passing rates.
• The Modulation Complexity Score for VMAT demonstrated moderate correlations (Spearman's rho ≈ 0.50-0.53).
• Aperture irregularity and average field width achieved acceptable true positive and false positive rates in identifying complex plans.

Conclusions:

• The Modulation Complexity Score is a promising metric for predicting VMAT measurement outcomes.
• Specific thresholds for aperture irregularity and average field width can aid in identifying complex plans.
• Incorporating these metrics into clinical workflows may reduce the need for extensive dose verification measurements.