TU‐G‐BRA‐04: Biological Optimization in Carbon Therapy

The application of high linear energy transfer (LET) radiation in modern radiation oncology, like carbon‐ion therapy, requires different concepts of treatment plan optimization when compared RT‐planning for photon beams. Although, by far not perfect, the standard strategy employs the concept of relative biological effectiveness (RBE), which converts the delivered physical particle dose into a radio‐biologically equivalent dose of low LET beams. In order to introduce the respective RBE models into the inverse planning process of particle therapy one directly aims to optimize the biological effect, mostly expressed in terms of a linear quadratic model (LQM) for a dose‐effect relationship. We will first introduce the general framework of biological optimization for inverse planning of intensity modulated particle therapy (IMPT). The effects of the intrinsic radiation quality on the design of treatment plans will be demonstrated for various forms of dose delivery methods, like spread‐out Bragg peaks (SOBP), distal edge‐tracking (DET) or 3D‐spot scanning and different clinical treatment sites. So far, the employed models only account for the most important radiobiological factor, the anticipated local LET distribution, while other additional factors like the oxygen enhancement ratio or the influence of different fractionation schemes are not considered explicitly. Finally, another important issue will be briefly mentioned, the robustness of biologically optimized treatment plans versus uncertainties in the dose delivery process or even the limited knowledge of the biological input parameters of the employed models that are predicting the biological effect. Some results in the framework of the worst‐case optimization will be discussed. Learning Objectives: 1. To review the framework of biological inverse planning of carbon therapy 2. To understand the potential and inherent limitations of the optimization approach