Clinical Applications of RBE in Carbon Ion Radiation Therapy: Current Status and Consensus Statements
Thomas Friedrich et al.
Carbon ion radiotherapy (CIRT) combines the physical advantages of the Bragg peak with the high linear energy transfer (LET) and increased relative biological effectiveness (RBE) of carbon ions. However, RBE is not a fixed value; it depends on physical and biological factors including LET, dose per fraction, tissue type, α/β ratio, oxygenation and the biological endpoint. Several models are currently used clinically, mainly the Local Effect Model (LEM) in Europe and the Mixed Beam Model/Microdosimetric Kinetic Model (MBM/mMKM) in Japan and other Asian centers. These models, together with different clinical conventions and parameters, may produce substantially different RBE-weighted or “clinical” doses for similar absorbed-dose distributions. The article therefore examines the consequences of these differences and proposes consensus statements regarding RBE modelling and dose translation. Model-dependent conversion requires consideration of dose, fractionation, LET distribution, beam configuration, target depth and model parameters. Increasingly, multi-model treatment planning and LET-based evaluation are being incorporated into clinical workflows.
In conclusions, no single RBE model can currently be considered universally superior. Dose prescriptions and OAR constraints must therefore be interpreted within their specific dose prescription system and validated clinically. Translation between models is feasible but is not unique and requires site-, dose- and fractionation-specific validation. Dual-model evaluation and LET distribution assessment may improve treatment robustness and safety. Standardized reporting and validated conversion procedures are essential for transferring protocols and conducting multinational clinical trials. Future developments should focus on improved RBE models, multi-model optimization and clinically validated strategies for incorporating LET into CIRT planning
Published by International Journal of Radiation Oncology, Biology, Physics 2026.
