A Monte Carlo Simulation Study for Production and Subsequent Interaction of Secondary Particles From Carbon-Ion Radiation Therapy in Water
D Johnson*, Y Chen, S Ahmad, Oklahoma Univ. Health Science Ctr., OKLAHOMA CITY, OKSU-E-T-726 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To classify and quantify the secondary particles produced from energetic carbon ion interactions in water, their dose averaged linear energy transfer(LET)s and their dose contributions.
Methods: A 1 mm diameter carbon ion pencil beam with various energies per nucleon was used in a GEANT4 simulation to interact with a 27 liter water phantom packed with 3000 rectangular detector sheets. The simulations involved processes arising from electromagnetic interactions (EMI) and hadronic interactions (HI). The EMI govern particles energy loss and straggling with atomic electrons and multiple scattering with atomic nuclei. The HI define ions elastic and inelastic scattering and nuclear interactions with atomic nuclei in the medium. Dose averaged LETs and dose contributions of primary and secondary particles were calculated.
Results: The percentages of the total dose deposited in regions A and B of the phantom by primary and secondary particles were 93.54%, 85.61% and 76.60% in A; 28.97%, 17.77% and 13.08% in B, for beam energy/nucleon of 155, 262 and 369 MeV, respectively, where region A covered beam path from phantom surface to 90% distal edge of Bragg peak and region B covered from 90% distal edge of Bragg peak to 5 cm past Bragg peak. The secondary particles proton, 11C, alpha and 11B contributed 4.17%, 9.26% and 15.21% in region A and 49.10%, 55.13% and 58.07% in region B for beam energy per nucleon of 155, 262 and 369 MeV, respectively.
Conclusion: The results of the simulations showed that those secondary particles that contributed major dose component had LETs < 100 keV/micrometer and those that had LETs > 600 keV/micrometer contributed < 0.3% towards the total dose.