A Quantitative Plan Quality Scoring Framework for Cross-Platform Comparison of VMAT and VMAT-Equivalent Left-Sided Breast Radiotherapy
Abstract
Purpose
To develop a quantitative plan quality scoring (PQS) tool for evaluation of left-sided breast radiotherapy plans and to compare performance across four platforms.
Methods
Left-sided breast radiotherapy plans were generated for each patient on four commercial platforms: Varian (VAR), Elekta (ELE), United Imaging Healthcare (UIH), and TomoTherapy (TOMO), using harmonized planning objectives and identical clinical dose constraints. All plans were created using VMAT or VMAT-equivalent rotational IMRT techniques. Plan quality was assessed using a composite PQS integrating five domains: target coverage, organ-at-risk (OAR) sparing, biological metrics, plan complexity, and delivery accuracy quantified by gamma analysis pass rate. Metrics were normalized and weighted to generate domain-specific sub-scores and an overall composite score. Results were summarized using median and interquartile range, with paired statistical comparisons to assess inter-platform differences.
Results
All plans met institutional clinical acceptance criteria. Conventional DVH-based metrics demonstrated comparable target coverage across platforms, with modest differences in conformity and dose gradient. The composite PQS revealed inter-platform differences in overall plan quality not fully reflected by dosimetric parameters. UIH achieved the highest overall PQS, driven by improved OAR sparing, including reduced low-dose exposure to the heart, bilateral lungs, breast, and abdominal organs, with favorable biological subscores. VAR and TOMO demonstrated intermediate performance. VAR benefited from high delivery accuracy and gamma pass rates, whereas TOMO showed advantages in OAR dose reduction but was penalized by higher monitor units and longer delivery times. ELE yielded the lowest composite score, primarily due to inferior OAR and QA-related subscores. TCP values were uniformly high across platforms, and NTCP values remained low and consistent with dosimetric trends.
Conclusion
The proposed PQS enables objective comparison of breast radiotherapy plan quality across platforms and provides a physics-based framework to identify trade-offs between dosimetric quality, delivery accuracy, and treatment efficiency.