Pignol J P, Slabbert J
Radiotherapy Department, Toronto-Sunnybrook Regional Cancer Centre, ON, Canada.
Can J Physiol Pharmacol. 2001 Feb;79(2):189-95.
Fast neutrons (FN) have a higher radio-biological effectiveness (RBE) compared with photons, however the mechanism of this increase remains a controversial issue. RBE variations are seen among various FN facilities and at the same facility when different tissue depths or thicknesses of hardening filters are used. These variations lead to uncertainties in dose reporting as well as in the comparisons of clinical results. Besides radiobiology and microdosimetry, another powerful method for the characterization of FN beams is the calculation of total proton and heavy ion kerma spectra. FLUKA and MCNP Monte Carlo code were used to simulate these kerma spectra following a set of microdosimetry measurements performed at the National Accelerator Centre. The calculated spectra confirmed major classical statements: RBE increase is linked to both slow energy protons and alpha particles yielded by (n,alpha) reactions on carbon and oxygen nuclei. The slow energy protons are produced by neutrons having an energy between 10 keV and 10 MeV, while the alpha particles are produced by neutrons having an energy between 10 keV and 15 MeV. Looking at the heavy ion kerma from <15 MeV and the proton kerma from neutrons <10 MeV, it is possible to anticipate y* and RBE trends.
与光子相比，快中子（FN）具有更高的放射生物学效能（RBE），然而这种增加的机制仍然是一个有争议的问题。在各种FN设施之间以及在同一设施中，当使用不同的组织深度或硬化过滤器厚度时，会观察到RBE的变化。这些变化导致剂量报告以及临床结果比较中的不确定性。除了放射生物学和微剂量学之外，表征FN束的另一种强大方法是计算总质子和重离子比释动能谱。在国家加速器中心进行了一组微剂量学测量之后，使用FLUKA和MCNP蒙特卡罗代码来模拟这些比释动能谱。计算出的能谱证实了主要的经典结论：RBE的增加与碳和氧原子核上（n，α）反应产生的慢能质子和α粒子都有关。慢能质子由能量在10 keV至10 MeV之间的中子产生，而α粒子由能量在10 keV至15 MeV之间的中子产生。从<15 MeV的重离子比释动能和<10 MeV的中子产生的质子比释动能来看，可以预测y*和RBE趋势。
