Program Information
An Analytical Approach for Calculating the Dose-Averaged LET in Spot-Scanning Proton Therapy with An Input Derived From a Monte Carlo Simulation
S Hirayama1*, T Matsuura1 , H Ueda1 , H Koyano1 , S Takao1 , T Fujii1 , Y Fujii2 , R Fujimoto2 , S Shimizu1 , K Umegaki1 , H Shirato1 , (1) Hokkaido University, Sapporo, Hokkaido, (2) Hitachi, Ltd., Omika, Ibaraki
Presentations
SU-K-108-3 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 108
Purpose: To develop an analytical model to compute the dose-averaged linear energy transfer (LETᵈ) based on the pencil beam algorithm (PBA) with an input derived from a Geant4 Monte Carlo simulation.
Methods: In our analytical model, we used the 1-dimensional LETᵈ for a pencil beam (LETᴱ), assuming that it depends on the energy (E) and depth in water. LETᵈ distribution induced by a pencil beam was calculated using Geant4 Monte Carlo simulation for each of 95 beam energies from 70.2 to 220 MeV and LETᴱ was derived from taking dose average over the whole transverse plane at each depth in water. The contributions from both primary and secondary protons were included. The LETᵈ distribution induced by multiple pencil beams was calculated in the same manner as the PBA, which models the dose distribution as the convolution of the fluence and kernel (a triple Gaussian function × integral depth dose distribution (IDD)), except that the IDD was replaced by LETᴱ × kernel divided by the total dose delivered to the voxel of interest. The LETᵈ distributions were compared between the analytical model and the Geant4 simulation for cubic (8 × 8 × 8 cm) and spherical targets (φ8 cm) at various depths in the homogeneous phantom (maximum ranges of 29, 21, and 13 cm), as well as in a clinical case of liver cancer (three fields, single field optimization plan).
Results: The differences in mean LETᵈ in the cubic and spherical targets were less than 0.04 and 0.06 keV/μm, respectively. In the clinical case, the difference in mean LETᵈ in the clinical target volume was less than 0.07 keV/μm.
Conclusion: We confirmed the usefulness of the developed algorithm. This algorithm can be used to evaluate biological doses, taking into consideration the dependence of relative biological effectiveness on LETᵈ.
Contact Email: