光中子在现代放射治疗领域的研究进展

The research progress of photo-neutron in the modern radiotherapy field

随着各种医用加速器新技术的提高和肿瘤患者数量的急剧增加,放射治疗已经成为治疗肿瘤的主要手段之一。医用加速器技术的不断进步,始终围绕着照射肿瘤的同时最大限度地保护正常器官而发展,但仍无法解决由于高能射线在治疗患者时所带来的辐射污染。高能粒子产生的次级粒子如光子、光中子及质子等对人体组织产生的生物效应同样不可忽略,并逐渐受到重视和广泛的研究。由于加速器机头内部构造的金属元素为铅,靶区主要为钨,光子能量达到>7 Me V时,会超过光核反应阈值从而产生中子,这一反应称为光核反应。国外放疗机构对光中子产生的剂量开展了广泛研究。基于参与复杂相互作用的粒子特点,通过蒙特卡罗模拟和实验测量两个途径来研究医用加速器产生的光中子通量和能谱等物理量。由于医用加速器设计不同(主要是机头内部),性能也有很大差别,因此光中子的通量、能谱和剂量也有不同的分布规律。在文献评阅的基础上,从蒙特卡罗模拟和实验测量两个方面阐述目前对医用加速器产生光中子的研究现状以及放射治疗过程中的辐射防护和引发第二原发癌的物理因素。

With the rapid development of new medical accelerators and the rapid increase in the number of patients with cancer, radiotherapy has become one of the main means to cure cancer. The unceasing progressive of medical accelerator technology always considers two aspects which includes the irradiation of the tumor, at the same time, and the maximum protection for normal organs, but these progressives never solve the radiation contamination problem from high-energy radiation when treat patient. Besides, the biological effects on human tissue of secondary particles produced by high energy particles, such as photons, photoneutrons, protons and so on, also shouldn＇t be neglected. These problems has been paid more and more attention and widely research. Because the internal structure of the head of accelerator is Pb elemental and the mainly target area is W（Tungsten） element, it will exceed the photon reaction threshold to produce neutrons when the photon energy reaches more than 7 MeV. This reaction is called photonuclear reaction. Foreign radiotherapy institutes have carried out a wide range studies on the dose of photo-neutrons. Based on the characteristics of particles involved in complex interactions, Monte Carlo simulation and experimental measurements are performed to study the photon flux and energy spectrum of medical accelerators. There are different distribution regulation of flux of light neutrons, energy spectrum and dose, due to different design of medical accelerator（ mainly is the interior of machine head） lead to different properties. This paper based on documents review, and the status of photon neutrons generated by medical accelerators, the radiation protection during radiotherapy and the exploration of the physical factors of the second primary cancer are expounded from Monte Carlo simulation and experimental measurement in this paper.