MM50加速器电子线降能器的研究

The Research of the Energy-Decelerator for MM50 Electron Beam

目的:研制医用电子回旋加速器MM50电子线降能器,以增加MM50加速器电子线能量档。方法:分析高能电子束与物质发生作用损失能量的机理,通过蒙特卡罗模拟计算对降能器进行理论研究,并选择适当的高纯材料和合理的厚度,设计并研制出多种降能器;研究MM50加速器治疗头靶转换器结构并进行适当改造,安装不同的降能器进行调试;实验测量电子线百分深度剂量曲线求得半峰值剂量深度R50(cm),再使用IAEA和NACP推荐的算法获得Ep0。结果:达到了将电子线能量降低2MeV,而没有X射线沾污影响的效果,从而使MM50加速器电子线能量档从现在3档(10MeV、25MeV、50MeV)变为6档(8MeV、10MeV、23MeV、25MeV、47MeV、50MeV)。结论:测量值与参考值吻合很好,并且各种方法所得的结果相一致。该方法可用于其他高能电子加速器、质子和其他重离子等加速器的能量转换或选择系统。

Objective： To study and fabricate the energy-decelerator ofMM50 （ the 50 MV Medical Microtron ） in order to increase the number of MM50 E-beam energy levels. Methods： To analyze the energy-lost mechanism of high-energy E-beam reaction with material, to study theoretically energy-decelerator by Monte Carlo analog calculation, to choice proper high pure material and reasonable thickness, to research and design different kinds of the energy-decelerator. We understand the MM50 head treatment and target exchanger then adjust a little properly, fit different kinds of the energy-decelerator installation, carry out the test, measure and do the experiment. Let E0 be E-beam energy, where Ep0 is average energy of phantom surface; the value can be gotten from R50（cm, Range to 50% max dose level or ionization） and the IAEA or NACP＇s algorithms. The R50can be measured with the Electron beam Percent-Depth Dose （PDD） in the water. Results： The energy-decelerator, which decrease E-beam energy 2 MeV, at same time no any effect to the intensity or dose rate of the E-beam and the X-ray pollution, hence increase the energy levels of E-beam from 3 levels （10 MeV,25 MeV,50 MeV） to 6 levels （ 8 MeV, 10 MeV,23 MeV. 25 MeV, 47 MeV ,50 MeV）.Conclusions： The measure value match with reference value very well and several methods meet the same result. This method can be used to other kind of high-energy electron accelerator, proton and other heavy ion accelerator etc. as energy conversion or choice system. Our next step will be to study the energy-decelerator which can decrease energw 5 MeV and 10 MeV.