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Quantified VMAT Plan Complexity in Relation to Measurement-Based Quality Assurance Results

M Nguyen*, G Chan, Juravinski Cancer Center, Hamilton, ON, CA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To verify the usage of quantified measures of treatment plan complexity as pre-treatment quality assurance tools to complement measurement-based patient specific quality assurance for VMAT.

Methods: 91 and 93 clinically approved VMAT plans delivered on a Varian TrueBeam and two TrueBeam STx linacs, respectively, were randomly selected. Measurements were performed with the IBA MatriXX Evolution 2D ion chamber array detector with an in-house polystyrene phantom. The measurements were compared to the corresponding plan dose maps generated by Philips Pinnacle (v9.10) using gamma analysis at the 3%/2mm and 2%/2mm criteria. Internal Pinnacle treatment files were analyzed to calculate complexity metrics for each treatment plan. Correlation and receiver operating characteristic curve analysis were performed to investigate the relationship between treatment plan complexity and agreement between measured and calculated dose distributions.

Results: Complexity metrics were generally found to have weak correlations to quality assurance results. However, extreme levels of complexity can suggest larger disagreement between dose distributions. The Modulation Complexity Score showed moderate correlations to the gamma passing rate, with Spearman’s rho values of 0.502 and 0.528 for the TrueBeam and TrueBeam STx respectively. The Aperture Irregularity identified 53% of all highly complex plans with a 9% false positive rate on the TrueBeam, and the Average Field Width identified 60% of all highly complex plans with an 8% false positive rate on the TrueBeam STx linacs.

Conclusion: This investigation indicates the potential use of complexity metrics as quality assurance tools in the planning process. Identification of highly complex plans would allow one to decide if plan modifications or patient-specific quality assurance measurements are required prior to treatments.

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Keywords

Quality Assurance, Treatment Verification, ROC Analysis

Taxonomy

TH- External Beam- Photons: Quality Assurance - IMRT/VMAT

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