JUNIOR INVESTIGATOR WINNER - Towards Radiation Therapy with Very High-Energy Electron Beams
M Bazalova1*, B Hardemark2, E Hynning2, M Dunning3, D McCormick3, M Liu4, S Tantawi3, A Dolgashev 3, A Koong1, P Maxim1, B Loo1, (1) Stanford University, Stanford, CA, (2) RaySearch Laboratories AB, Stockholm, Sweden, (3) SLAC National Accelerator Laboratory, Menlo Park, CA, (4) UCLA, Los Angleles, CAWE-C-108-1 Wednesday 10:30AM - 12:30PM Room: 108
Purpose: To experimentally validate Monte Carlo (MC) simulations for dose calculations with very high-energy electron (VHEE) beams in the presence of heterogeneities and to use MC simulations for treatment planning optimization of ultra-fast radiation therapy with VHEE beams.
Methods: Polystyrene phantom with heterogeneities made of nine materials of various thicknesses was irradiated at a VHEE beam line at SLAC National Accelerator Laboratory. Films were used to measure the dose delivered to the phantom by 60-110MeV VHEE beams of 0.6-2.2mm in size. A MC model of the beam line was built and validated against the experimental data based on percentage depth-dose (PDD) curves. The MC validated code was used for VHEE radiotherapy planning of three patients. More specifically, MC beamlets were exported into a modified version of RayStation for spot-scanning optimization. The quality of VHEE dose distributions as a function of electron beam energy, beamlet size and spacing, source-to-isocenter distance, and number of beams was studied.
Results: MC calculated PDD curves for heterogeneous phantoms were in agreement with the experimental PDD curves obtained at the VHEE beam line for all beam energies and beam sizes. VHEE treatment planning optimization study for a pediatric patient brain tumor revealed that significant normal tissue sparing was achieved in 60-100MeV VHEE plans compared to the state-of-the-art 6MV VMAT plan. The mean dose to the cochleae was by 56-72% lower in the VHEE plans. Out of the studied parameters, electron beam energy had the largest effect on the quality of VHEE treatment plans. In order to generate a VHEE plan matching a VMAT plan for a large patient, VHEE beams of 100-150MeV are needed.
Conclusion: We have validated VHEE beam MC dose calculations and we have developed a MC/RayStation treatment planning optimization tool for evaluation of the potential to rapidly treat cancer with VHEE beams.
Funding Support, Disclosures, and Conflict of Interest: This work has been supported by the 2012 AAPM Research Seed Grant.