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. 2024 Nov;34(4):555-564.
doi: 10.1016/j.zemedi.2023.02.003. Epub 2023 Mar 29.

Reduction of patient specific quality assurance through plan complexity metrics for VMAT plans with an open-source TPS script

Klara Uher  1 , Stefanie Ehrbar  1 , Stephanie Tanadini-Lang  1 , Riccardo Dal Bello  2
Affiliations

Reduction of patient specific quality assurance through plan complexity metrics for VMAT plans with an open-source TPS script

Klara Uher et al. Z Med Phys. 2024 Nov.

Abstract

Purpose: Volumetric modulated arc therapy (VMAT) is a widespread technique for the delivery of normo-fractionated radiation therapy (NFRT) and stereotactic body radiation therapy (SBRT). It is associated with a significant hardware burden requiring dose rate modulation, collimator movement and gantry rotation synchronisation. Patient specific quality assurance (PSQA) guarantees that the linacs can precisely and accurately deliver the planned dose. However, PSQA requires a significant time allocation and class solutions to reduce this while guaranteeing the deliverability of the plans should be investigated.

Methods: In this study, an in-house developed Eclipse Scripting API (ESAPI) script was used to extract five independent plan complexity metrics from N = 667 VMAT treatment fields. The correlation between metrics and portal dosimetry measurements was investigated with Pearson correlation, box plot analysis and receiver operating characteristic curves, which were used to defined the best performing metric and its threshold.

Results: The incidence of fields failing the clinical PSQA criteria of 3%/2mm (NFRT) and 3%/1.5mm (SBRT) was low (N = 1). The mean MLC opening was the metric with the highest correlation with the portal dosimetry data and among the best in discriminating the requirement of PSQA. The thresholds of 16.12 mm (NFRT) and 7.96 mm (SBRT) corresponded to true positive rates higher than 90%.

Conclusions: This work presents a quantitative approach to reduce the time allocation for PSQA by identifying the most complex plans demanding a dedicated measurement. The proposed method requires PSQA for approximately 10% of the plans. The ESAPI script is distributed open-source to ease the investigation and implementation at other institutions.

Keywords: ESAPI; Patient specific quality assurance; SBRT; TPS scripting; VMAT.

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Conflict of interest statement

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1
Figure 1
Pearson correlation matrix between complexity metrics and GPR for VMAT-FF fields.
Figure 2
Figure 2
Pearson correlation matrix between complexity metrics and GPR for VMAT-FFF fields.
Figure 3
Figure 3
Boxplot analysis for MMO and gamma analysis with 3%/2mm criteria (VMAT-FF, left) and 3%/1.5mm (VMAT-FFF, right). Whiskers extend to furthest data point that is within 1.5 IQR and outliers are not shown.
Figure 4
Figure 4
ROC curves for VMAT-FF (left) and VMAT-FFF (right) fields generated with the strictest gamma analysis criteria and threshold set at 97.5%.
Figure 5
Figure 5
Dependency of true positive rate and distance from the perfect classifier on the MMO threshold for VMAT-FF (left) and VMAT-FFF (right).
See this image and copyright information in PMC

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