SU-E-T-731: Implementation of a One Dimensional Analytical Model for Calculating Three Dimensional Linear Energy Transfer in Proton Radiotherapy

Abstract

Purpose: To develop and implement a three dimensional, analytical model for linear energy transfer (LET) calculations of a clinical proton beam based on a one dimensional model presented in the literature for use in calculating variable relative biological effectiveness (RBE) values within a patient treatment plan.Methods: Implementation of the one dimensional analytical model was performed in MATLAB and confirmed with Monte Carlo (MC) results for a proton beam matching the beam specifications of a clinical proton beam. Application to three dimensional geometries was achieved by referencing values to the generated one dimensional array to corresponding distances from a 4cm × 4cm planar source, for a water phantom. The three dimensional model was then applied to a prostate plan and compared to MC results.Results: One dimensional implementation of the model to a 70MeV and 160MeV proton beam showed good agreement with MC results along the proximal portion of the beam path and agreement within 8% and 13% along the distal 5mm of the beam path for each respective beam. Implementation in a three dimensional water phantom achieved an agreement within 0.5 keV/micron for 60.3% of all voxels and 2.5keV/micron for 98.3% of all voxels for a 160MeV plane source beam. Of the voxels that differed by more than 2.5keV/micron, 95.5% differed within the range of experimental uncertainty in the MC results. Conclusions: An analytical model for LET calculations in proton therapy may be used to quickly and efficiently estimate LET values within a three dimensional volume. This allows for the calculation of variable RBE values in a patient volume and the possibility of optimizing plans based on the biological effect of proton radiotherapy.