Monte Carlo Dose Simulation For Carbon Ion Cancer Therapy
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Date
2015
Authors
Ying, Chee Keat
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Heavy-particle therapy such as carbon ion therapy is more popular nowadays for charged particle cancer therapy. This is due to its characteristics of the Bragg’s peak which has relatively low entrance dose and gives almost no residual radiation dose beyond the tumor location. An effective radiation therapy treatment planning is achieved by making accurate dose calculation and by minimizing the fragmentation doses to the distal edge of the target tumor and surrounding tissues. This research has two parts. In the first part, Geant4 based Monte Carlo (MC) method is used to simulate the radiation transportation and dose distribution in tissue-like material. In the second part, this study presents a new method based on a monolithic ΔE-E telescope to characterize the radiation field produced by the carbon ion beam in terms of particle components which make up the mixed radiation field as well as the microdosimetric spectra allowing a better determination of the Relative Biological Effectiveness (RBE). The main objectives in the study have been achieved. The carbon ion beams at the isocentric gantry nozzle for the therapeutic energy of 290, 350 and 400 MeV/u respectively were simulated, with the same setting as the experimental work carried out at the treatment room at Heavy Ion Medical Accelerator (HIMAC), National Institute of Radiological Sciences (NIRS), Chiba, Japan. The work was to confirm the accuracy and quality of the dose distributions by Geant4 MC methods. Adjustment for the Geant4 code was made to suit the measurement data as close as possible and the simulation dose distributions were compared with measurement results for Bragg peak and the spread-out Bragg peak
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(SOBP) respectively. The responses of the ΔE-E telescope at defined positions along the Bragg peak were also studied at Centre of Medical Radiation Physics (CMRP), University of Wollongong. The results of comparisons show the Bragg peak depth-dose distributions in the simulated data correspond well with the measurements. The deviation of Bragg peak positions (from 1.99% to 2.08%), Peak-plateau ratio (from 0.40% to 9.87%), FWHM ( from 9.83% to 14.89%), Distal fall-off 80%-20% ( from 6.82% to 63.96%) were presented. However, the simulation of SOBP distributions was slightly underestimated compared with the measurements. The maximum deviations at the peak regions between simulations and measurements for energies of 290, 350 and 400 MeV/u are 15%, 12% and 18% respectively. The microdosimetric spectra derived from the ΔE stage response at both in-field and out-of-field regions are presented along with the two-dimensional scatter plots of energy deposition in ΔE and E stages of the telescope detector in coincidence. Partial contribution from nuclear fragments of 1H, 4He, 3He, 7Li, 9Be, 11B have been analyzed for each position. This work shows the ΔE-E telescope can be used effectively to characterize the mixed radiation field produced by the carbon ion therapeutic beam and also to measure the microdosimetric spectra, which currently cannot be achieved using Tissue Equivalent Proportional Counter (TEPC).
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Keywords
Carbon ion therapy , for charged particle cancer therapy.