RBE for proton radiation therapy – a Nordic view in the international perspective

Abstract

Background: This paper presents an insight into the critical discussions and the current strategies of the Nordic countries for handling the variable proton relative biological effectiveness (RBE) as presented at The Nordic Collaborative Workshop for Particle Therapy that took place at the Skandion Clinic on 14th and 15th of November 2019. Material and methods: In the current clinical practice at the two proton centres in operation at the date, Skandion Clinic, and the Danish Centre for Particle Therapy, a constant proton RBE of 1.1 is applied. The potentially increased effectiveness at the end of the particle range is however considered at the stage of treatment planning at both places based on empirical observations and knowledge. More elaborated strategies to evaluate the plans and mitigate the problem are intensely investigated internationally as well at the two centres. They involve the calculation of the dose-averaged linear energy transfer (LET d ) values and the assessment of their distributions corroborated with the distribution of the dose and the location of the critical clinical structures. Results: Methods and tools for LET d calculations are under different stages of development as well as models to account for the variation of the RBE with LET d , dose per fraction, and type of tissue. The way they are currently used for evaluation and optimisation of the plans and their robustness are summarised. A critical but not exhaustive discussion of their potential future implementation in the clinical practice is also presented. Conclusions: The need for collaboration between the clinical proton centres in establishing common platforms and perspectives for treatment planning evaluation and optimisation is highlighted as well as the need of close interaction with the research academic groups that could offer a complementary perspective and actively help developing methods and tools for clinical implementation of the more complex metrics for considering the variable effectiveness of the proton beams.

Does the uncertainty in relative biological effectiveness affect patient treatment in proton therapy?

“…1). Whether the increase of the RBE towards the distal edge is a clinical issue, or the use of a fixed RBE of 1.1 is an adequate clinical solution is under debate, and there is an increasing awareness of clinical uncertainties in proton therapy arising from RBE issues [2,[7][8][9].…”

Neurocognition and mean radiotherapy dose to vulnerable brain structures: new organs at risk?

“…For systematic evaluation of clinical outcomes and to address for larger cohorts, medical, neurocognitive and educational data needs to be systematically collected in national and/or international quality registries [56,62,63]. For proton RT there is a need for collaboration between clinical proton centers to establish common platforms and perspectives for optimization and treatment planning evaluation and actively help developing methods and tools for clinical implementation of the more complex metrics [64]. Since august 2015 all children in Sweden are offered proton RT at the Skandion clinic in Uppsala, without additional costs for the families [65], if this treatment is preferable.…”

How can we consider variable RBE and LETd prediction during clinical practice? A pediatric case report at the Normandy Proton Therapy Centre using an independent dose engine

“…Recent reports discuss current and future strategies using FRoG and comparable systems to establish refined treatment planning perspectives between Nordic PT centers in the assessment of LET and/or variable D RBE distributions within OARs [ 46 ]. Similarly, a beam orientation optimization technique based on LET reduction in OARs has been investigated within a research platform demonstrating the importance of such beam parameters in OAR LET reduction [ 47 ].…”