RATS: A Framework for Robustness Comparison of IMPT and IMRT In Prostate Dominant Intraprostatic Lesion (DIL) Boost Planning
Abstract
Purpose
To introduce and apply a analytical-driven robustness evaluation framework, Robust Analysis Treatment Score (RATS), for systematic comparison of intensity-modulated proton therapy (IMPT) and intensity-modulated radiation therapy (IMRT) treatment plans for prostate cancer focal dominant intraprostatic lesion (DIL) boosts under clinically relevant geometric and range uncertainties.
Methods
Four prostate cancer patients were retrospectively replanned, generating twelve plans per patient using IMPT and IMRT, including nominal, robustly optimized, and geometrically expanded strategies. IMPT plans were evaluated across 39 combined geometric and range uncertainty scenarios, while IMRT plans incorporated 19 geometric perturbation scenarios. Dose-volume histogram data were extracted for targets and organs at risk and processed using a custom analysis workflow. Plan robustness was quantified using the RATS framework, which combines weighted uncertainty likelihood, organ-specific priority, constraint importance, and modeled tumor control and normal tissue complication probabilities into a composite score. To enable direct modality comparison, photon plan scores were normalized to account for the reduced number of evaluated uncertainty scenarios.
Results
Moderately robustly optimized proton plans consistently achieved the highest RATS values across all patients, outperforming nominal proton plans, geometrically expanded proton plans, and all photon plans in over 90 percent of evaluated uncertainty scenarios. Robust optimization yielded improved preservation of target coverage and organ-at-risk sparing relative to margin-based expansion strategies. Photon plans demonstrated a monotonic decline in robustness with increasing geometric uncertainty. While interpatient variability was observed, robust IMPT plans maintained superior performance across diverse anatomical conditions.
Conclusion
RATS provides a quantitative, customizable framework for the assessment of treatment plan robustness under uncertainty. This study demonstrates that moderate robust optimization in IMPT yields superior robustness compared to geometric expansion approaches and IMRT for focal prostate DIL boosts. The framework shows strong potential for objective robustness evaluation and comparative planning studies in advanced radiotherapy.