Program Information
Robust Radiobiological Optimization of Ion Beam Therapy with Monte Carlo Microdosimetric-Kinetic Model
J Ma1*, L Courneyea2 , H Wan Chan Tseung3 , C Beltran4 , M Herman5 , N Remmes6 , (1) Mayo Clinic, Rochester, MN, (2) Sunnybrook Health Sciences Centre, Toronto, ON, (3) Mayo Clinic, Rochester, MN, (4) Mayo Clinic, Rochester, MN, (5) Mayo Clinic, Rochester, MN, (6) Mayo Clinic, Rochester, MN
Presentations
SU-F-205-6 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: 205
Purpose: Radiobiological optimization may be essential for ion beam therapy with high linear energy transfer (LET), but it is complicated by the dependence of relative biological effectiveness (RBE) on LET, tissue (α/β), physical dose, and the setup and range uncertainties. The goal of this work is to develop a robust radiobiological optimization tool for scanning beam ion therapy based on an Monte Carlo (MC) implementation of the microdosimetric-kinetic model (MKM).
Methods: In-house particle transport package placed ion beam spots in targets. For each placed spot, physical dose and saturation corrected dose mean specific energy (z*) were calculated by an MKM implementation (Sato’s model) with TOPAS MC. Intensity modulated multi-field optimization was carried out using a gradient based iterative method for RBE-based biological dose (BD). Tissue specific α/β values and z* were used in the RBE calculation and RBE was updated during the optimization as voxel physical dose varied. The robust optimization method was developed based on dose-volume objective function computed under setup and range uncertainties.
Results: Intensity modulated ion therapy reduced the BD in relevant critical structures. Trade-offs between different ions were observed. For test cases, carbon beam entrance BD was 25% lower than the entrance BD from a proton beam with comparable BD target coverage. However, at 20% of target prescription dose, the carbon beam exit BD extended ~2mm beyond the proton beam dose for a target at ~10cm depth. Helium beams reduced entrance BD by approximately 10% while maintaining a similar exit dose compared to protons.
Conclusion: A Monte Carlo based radiobiological robust optimization system was developed. It calculated RBE with a microscopic model to incorporate RBE dependence on physical dose, α/β, radiation quality, and model parameters such as the cell nuclear size. Advantages and limitations of different ion beams were demonstrated.
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