Abstract
Variations in proton relative biological effectiveness (RBE) with dose averaged linear energy transfer (LET) remain one of the largest sources of uncertainty in proton radiotherapy. Biological robust LET based optimization has been introduced into some clinical treatment planning systems (TPS) to avoid normal tissue toxicity (Monte Carlo (MC) based calculation RaySearch commercial TPS). This work aims to introduce a new single cylindrical sensitive volume (SV) SOI microdosimeter modelling a biological cell using a 3D detector technology and can be operated in high intensity pencil beam scanning (PBS). The microdosimeter was applied for LET verification computed in a MC dose engie of RaySearch TPS. Various treatment plans were generated in a research version of RayStation v6R TPS using pencil beam scanning at University Medical Center Groningen facility, the Netherlands. Two plans were created consisting of a single pristine Bragg peak of 70 MeV and 130 MeV in a homogeneous water phantom and three PBS treatment plans were created to treat a spherical target with a 5 cm diameter with uniform dose coverage, in the CIRS 731- HN anthropomorphic head and neck phantom. The silicon microdosimeter system was used to measure these plans and to compare with Geant4 simulation for the same configuration and setup. Based on measured microdosimetric quantity, the dose mean lineal energy (yD), an additional dose for each plan was obtained. It has been observed that additional dose could increase up to 47% compared to prescribed physical dose assuming constant RBE of 1.1. Good agreement was observed between additional dose obtained based on measured yD and calculated LET by RaySearch TPS. This work ahs demonstrated that the single SV silicon microdosimeter system developed by CMRP and fabricated at SINTEF is a very useful and unique tool to validate LET computed in RaySearch TPS and will allow new quality assurance for biologically optimized proton therapy planning.