Abstract
Aperture-based complexity metrics have been suggested as a method to score complexity of volumetric modulated arc therapy (VMAT) plans. The purpose of this study was to evaluate the edge area metric (EAM) for clinical VMAT plans on a control point and treatment plan level. EAM on a control point level was evaluated based on film measurements of 18 static beam openings originating from VMAT plans. EAM on a treatment plan level (arithmetic mean value of EAM scores for control points) was evaluated based on measurements with the Delta4® for 200 VMAT plans for four different treatment sites: pelvic, thorax, head and neck, and prostate. Measurements were compared to calculations and dose difference and gamma pass rates were evaluated. EAM scores on a control point level correlated with Pearson's r-values of -0.96 and -0.77 to dose difference and gamma pass rates, respectively. The prostate plans had the highest average EAM score. A connection between smaller PTVs and higher EAM scores was found. No correlation between the evaluation result and EAM on a plan level was found. EAM on a control point level was shown to correlate to the difference between measured and calculated 2D dose distributions of clinical VMAT beam openings. No correlation was found for EAM on a plan level for clinical treatment plans.
Highlights
Volumetric modulated arc therapy (VMAT) involves simultaneous alteration of the beam opening formed by multi-leaf collimators (MLC), gantry speed, and dose rate, for beam modulation during treatment [1]
The average edge area metric (EAM) score for all plans was 0.59 and 0.67, 0.59, 0,58 and 0,52 for prostate plans, thorax plans, head and neck (H&N) plans, and plans planned for larger targets in the pelvic, respectively
The proportion of the prostate plans with an EAM score higher than the total average (0.59) was 94% and the corresponding proportion for the plans planned for larger targets in the pelvic was 6%
Summary
Volumetric modulated arc therapy (VMAT) involves simultaneous alteration of the beam opening formed by multi-leaf collimators (MLC), gantry speed, and dose rate, for beam modulation during treatment [1]. Aperture-based complexity metrics have been suggested as a method to score complexity of volumetric modulated arc therapy (VMAT) plans. Materials and methods: EAM on a control point level was evaluated based on film measurements of 18 static beam openings originating from VMAT plans. EAM on a treatment plan level (arithmetic mean value of EAM scores for control points) was evaluated based on measurements with the Delta4® for 200 VMAT plans for four different treatment sites: pelvic, thorax, head and neck, and prostate. Results: EAM scores on a control point level correlated with Pearson’s r-values of − 0.96 and − 0.77 to dose difference and gamma pass rates, respectively. Conclusions: EAM on a control point level was shown to correlate to the difference between measured and calculated 2D dose distributions of clinical VMAT beam openings. No correlation was found for EAM on a plan level for clinical treatment plans
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