Combined RBE and OER optimization for proton therapy

A paper exploring the combination of Oxygen Enhancement Ratio and Relative biological effectiveness in proton therapy treatment planning. First author Helge Henjum (helge.henjum@uib.no) is Post Doc. in the Bioproton project.

The effect of protons in hypoxic cells is a topic of high clinical relevance as hypoxia is related to poor treatment outcome. A combined RBE and OER weighted dose (ROWD) calculation method was implemented in a FLUKA Monte Carlo (MC) based treatment planning tool. The method is based on the linear quadratic model, with α and β parameters as a function of the OER, and therefore a function of the linear energy transfer (LET) and partial oxygen pressure (pO₂). Proton therapy plans for two head and neck cancer (HNC) patients were optimized with pO₂ estimated from [¹⁸F]-EF5 positron emission tomography (PET) images. For the ROWD calculations, an RBE of 1.1 (RBE_1.1,OER) and two variable RBE models, Rørvik (ROR) and McNamara (MCN), were used, alongside a reference plan without incorporation of OER (RBE_1.1).

The FLUKA MC based tool was able to optimize proton treatment plans taking the tumor pO₂ distribution from hypoxia PET images into account. Independent of RBE-model, both elevated LET and physical dose were found in the hypoxic regions, which shows the potential to increase the tumor control compared to a conventional optimization approach.