Study Of The Effect Of Range Shitfer On The Medical Carbon Ion Beams Using Geant4Method

In recent years, the radiotherapy of heavy ions have been developed rapidly.Beams of carbon ions have favourable physical and biological properties, which is itsBragg peak depth dose profile and high relative biological effectiveness, for the use inradiotherapy. So the beams of carbon ions have received extensive attention in theradiotherapy research. The configuration of carbon ion beams is shaped to the tumor’sconfiguration by beam delivery system before the carbon ion beams arrive at thehuman body. The beam delivery systems presently in use and designed for the heavyion treatment are passive beam shaping techniques and active beam delivery systems.They are have an energy variation device, range shifter, to make the conformalradiotherapy come true. So it’s necessary to study the effect of the range shifter to thebeams of carbon ions.The angle and energy straggling of12C6+beams was simulated using MonteCarlo method of Geant4in this article, and the energy of12C6+beams range from80MeV/u to360MeV/u, while the mass thickness of the target, PMMA、Al、Cu、Pb,range from0.5g/cm2to5.5g/cm2. Then the effect of the energy of12C6+、the materialand thickness of the range shifter to the12C6+beam were discussed quantitatively. Atlast, the best material for range shifter was select by giving and analysis the formulaof water equivalent thickness. Then the Bragg peak of12C6+beam which have passedthrough range shifter were compared to the Bragg peak of mono-energetic12C6+beam,and the effect of the range shifter’s to the Bragg peak was qualitatively analyzed. Theconclusions as follows:(1) The angle straggling are influenced by the carbon ions’ energy, the materialand thickness of range shifter. The rule is: the degree of angle straggling is increasedwith the decrease of carbon ions’ energy and the increase of Z and mass thickness ofrange shifter.(2) The energy straggling are mainly influenced by the material and thickness of range shifter. The degree of energy straggling is increased with the increase of (Z/A)and mass thickness of range shifter. Besides, the energy of carbon ions also influenceenergy straggling and this kind of effect is every small, so the energy straggling doesnot change along with the energy in the approximate case.(3) The material with a smaller atomic number Z is more fit to be the material ofrange shifter. Besides, the effect degree of range shifter to Bragg peak increases withthe increase of range shifter’s mass thickness and the decrease of carbon ions’ energy.