Room: Room 207
Purpose: To develop an easily implementable algorithm for the rapid generation of a uniform one-dimensional biological dose, namely the product of physical dose and the relative biological effectiveness (RBE), within a target volume using scanned ion beams.
Methods: Protons, helium, and carbon ions were selected. Geant4 Monte Carlo simulations were performed to generate physical dose and repair-misrepair-fixation (RMF) model related radiobiological parameters for each ion beamlet. These basic data were then used in the downstream biological dose optimizations. The optimization algorithms were implemented using the Python programming language by invoking RMF model in the iterative process to calculate RBE. The desired target RBE-weighted dose (RWD) was set as 3.8 Gy (RBE) corresponding to the cell survival of 10% for the H460 cell line irradiated with 137Cs photons in previous experiments.
Results: A uniform RWD distribution in a target from 5 to 10 cm in a water phantom was obtained. The relative difference was within Â±0.3% between the desired and calculated RWD for most of the target region for the selected ions. The proton RBE increases from 1.10 to 1.25 within the target, and sharply increases to 1.72 at the distal edge. The helium ion RBE increases from 1.3 to 1.8 within the target and increases up to 2.3, while it decreases in the distal edge and then increases in the fragmentation tail. The carbon ion RBE increases from 1.9 to 3.9 within the target and increases up to 4.9, while it decreases sharply in the distal edge and continues to decrease in the fragmentation tail.
Conclusion: We have demonstrated the feasibility and flexibility of the combined use of Monte Carlo simulations and the Python language to perform biological dose optimizations for scanned ion beams. The mechanism-based RMF model provides fast and reliable RBE calculations for both primary and secondary particles.