Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Monte-Carlo (MC) simulations may allow for reducing range margins and applying variable relative-biological-effectiveness (RBE) models in proton therapy. Here, an approach is presented to support treatment planning of patients by highlighting regions with increased dose uncertainties originating from dose calculation and the assumption of a constant RBE of 1.1.
A software framework was developed and experimentally validated, which simulates proton plans at the University Proton Therapy Dresden (UPTD) using the MC tool TOPAS. It is based on a commissioned model of the UPTD treatment head in double-scattering mode. Clinical treatment plans and computed tomography datasets were imported in DICOM format. MC-based dose distributions were compared with dose distributions received from the clinically applied treatment planning system (TPS) XIO, Elekta. Obtained dose, linear-energy-transfer (LET), and modelled RBE maps (using experimental in vitro data) were imported into the TPS RayStation, RaySearch for plan evaluation.
TPS doses above the 95% iso dose level are reproduced within gamma pass rates GPR ≥ 98%, when applying 1 mm local and 2 % dose gamma criterion. Dose differences reached values up to 8 Gy for field volumes up to 4 cm 3 , particularly at regions with high-density gradients (e.g. bone and air cavities) and at the field edges. LET and variable RBE hot spots were obtained at (distal) field edges while at the field center RBE values below 1.1 were predicted. Clinical dose values differed by up to 10 Gy using either the assumption of a constant or a variable RBE.
The treatment planning and delivery workflow at UPTD was mapped in a MC simulation. In general, good agreement between TPS and MC clinical dose values was found. However, relevant clinical dose differences were obtained and emphasise the necessity of using MC to enhance the physical and biological dose prediction in patients.