KEY POINTS
- Methodological study developing probabilistic dose-dependent dose-averaged linear energy transfer constraints for proton therapy toxicity interpretation.
- The framework used linear quadratic-based variable relative biological effectiveness models with 4 published parametrizations: Wedenberg, Carabe, McNamara, and Lyngholm.
- Published dose and dose-averaged linear energy transfer data from 11 clinical studies were compared across 5 toxicity endpoints: brainstem necrosis, brain necrosis, radiation-induced brain image change, rib fracture, and osteoradionecrosis.
- Probabilistic constraints generally agreed with published clinical constraints for brainstem necrosis, radiation-induced brain image change, and osteoradionecrosis, with reported tolerance limits lying within or near the 95% confidence intervals.
- Dose and dose-averaged linear energy transfer combinations observed in patients with toxicity consistently exceeded the upper bounds of the constraint envelopes, while constraint resolution was limited at higher linear energy transfer values.
CLINICAL TAKEAWAY
This work supports moving beyond single-value linear energy transfer thresholds toward dose-dependent proton plan evaluation. The framework is useful for interpreting toxicity signals and comparing relative biological effectiveness models, especially where dose and linear energy transfer jointly drive risk. But it is not a new clinical constraint set: the analysis is literature-based, heterogeneous across endpoints and calculation platforms, and limited by sparse clinical sampling at high linear energy transfer.
SOURCE
International Journal of Radiation Oncology, Biology, Physics