Abstract
In medical physics it is desirable to have a Monte Carlo code that is less complex, reliable yet flexible for dose verification, optimization, and component design. TOPAS is a newly developed Monte Carlo simulation tool which combines extensive radiation physics libraries available in Geant4 code, easyto-use geometry and support for visualization. Although TOPAS has been widely tested and verified in simulations of proton therapy, there has been no reported application for carbon ion therapy. To evaluate the feasibility and accuracy of TOPAS simulations for carbon ion therapy, a licensed TOPAS code (version 3_0_p1) was used to carry out a dosimetric study of therapeutic carbon ions. Results of depth dose profile based on different physics models have been obtained and compared with the measurements. It is found that the G4QMD model is at least as accurate as the TOPAS default BIC physics model for carbon ions, but when the energy is increased to relatively high levels such as 400 MeV/u, the G4QMD model shows preferable performance. Also, simulations of special components used in the treatment head at the Institute of Modern Physics facility was conducted to investigate the Spread-Out dose distribution in water. The physical dose in water of SOBP was found to be consistent with the aim of the 6 cm ridge filter.
Highlights
Over the past 30 years, ion beam radiotherapy using particles like proton, helium, carbon ions has been gradually and slowly increasingly in popularity in radiation oncology [1,2,3].The inverted depth dose profile ⎯the increase of dose along the penetration depth and a sharp drop after the Bragg Peak ⎯ make ion beams an ideal tool for treatment of the deepseated tumours [1,2,3,4,5,6,7]
TOPAS is well-designed to make the simulation for Ion Beam Radiotherapy, both proton and carbon ions, easier and more efficient
The default physics models in TOPAS are elaborately chosen and have been validated with a high accuracy. When it comes to the high energetic carbon ions like 400 MeV/u or higher, the G4QMD model is recommended instead of the BIC model
Summary
Over the past 30 years, ion beam radiotherapy using particles like proton, helium, carbon ions has been gradually and slowly increasingly in popularity in radiation oncology [1,2,3].The inverted depth dose profile ⎯the increase of dose along the penetration depth (the Bragg Peak) and a sharp drop after the Bragg Peak ⎯ make ion beams an ideal tool for treatment of the deepseated tumours [1,2,3,4,5,6,7]. The excellent dose profile is further boosted by an additional increase in the relative biological effectiveness (RBE) along the depth till the end of the particle range [2,3,4, 6, 8].Because of the distinguished physical and biological properties, carbon ion radiotherapy (CIRT) has become a unique research focus around the world. Encouraged by the superior clinical results, two dedicated heavy-ion therapy facilities are under construction in Lanzhou and Wuwei, China, respectively. Both of them are expected to start treatment in the few years [6]
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