Variable proton RBE mitigation approaches for clinical practice

Chairs:

• Dirk Wagenaar
• Alexandru Dasu

Motivation

Proton therapy centers increasingly recognize that the relative biological effectiveness (RBE) of protons may exceed the clinically assumed value of 1.1 near the distal end of the proton beam. This raises important questions for patient safety and treatment optimization, particularly in situations where critical organs are located close to the end-of-range of the beam. As clinical evidence accumulates and awareness grows, there is a clear need for guidance on how to address this issue in routine clinical practice.

A previous multi-disciplinary meeting organized by EPTN in 2023 resulted in consensus recommendations encouraging centers to report quantities beyond physical dose and constant RBE. While this represented an important step toward improving the understanding of proton beam biological effects, many centers are now seeking practical guidance on how to move from reporting these quantities to actively using them to improve patient care. In addition, the meeting highlighted a need for education on this topic, although the most effective format for such educational efforts remains unclear.

In recent years, treatment planning systems have increasingly incorporated tools to evaluate or mitigate enhanced RBE effects, including linear energy transfer (LET) distributions, variable RBE estimates, and LET-based optimization strategies. Although these approaches have been extensively investigated in the scientific literature, their clinical implementation remains challenging due to limited shared experience and uncertainty regarding best practices.

Workshop focus

This workshop will focus on clinically applicable solutions for incorporating LET and RBE-related information into proton therapy treatment planning and evaluation. Rather than emphasizing research that may take several years to translate into practice, the goal is to discuss practical approaches that can be implemented within current clinical workflows, enabling centers to translate available tools and knowledge into immediate improvements in patient care.

Potential outcomes

• Pre-meeting survey on the current clinical use of variable RBE mitigation strategies
• Shared practical experiences from proton therapy centers currently implementing LET and RBE evaluation tools in clinical workflows
• Identification of clinically feasible strategies for evaluating and mitigating enhanced RBE effects in treatment planning
• Increased harmonisation of use of LET and RBE-related quantities across European proton therapy centers
• Practical guidance for transitioning from reporting advanced quantities to using them for clinical decision-making
• Identification of training needs for the field regarding variable proton RBE evaluation and mitigation