Pignol J P, Cuendet P, Brassart N, Fares G, Colomb F, M'Bake Diop C, Sabattier R, Hachem A, Prevot G
Service de Radiothérapie, Hôpital du Hasenrain-87, Mulhouse, France.
Med Phys. 1998 Jun;25(6):885-91. doi: 10.1118/1.598264.
Boron neutron capture enhancement (BNCE) of the fast neutron irradiations use thermal neutrons produced in depth of the tissues to generate neutron capture reactions on 10B within tumor cells. The dose enhancement is correlated to the 10B concentration and to thermal neutron flux measured in the depth of the tissues, and in this paper we demonstrate the feasibility of Monte Carlo simulation to study the dosimetry of BNCE. The charged particle FLUKA code has been used to calculate the primary neutron yield from the beryllium target, while MCNP-4A has been used for the transport of these neutrons in the geometry of the Biomedical Cyclotron of Nice. The fast neutron spectrum and dose deposition, the thermal flux and thermal neutron spectrum in depth of a Plexiglas phantom has been calculated. The thermal neutron flux has been compared with experimental results determined with calibrated thermoluminescent dosimeters (TLD-600 and TLD-700, respectively, doped with 6Li or 7Li). The theoretical results were in good agreement with the experimental results: the thermal neutron flux was calculated at 10.3 X 10(6) n/cm2 s1 and measured at 9.42 X 10(6) n/cm2 s1 at 4 cm depth of the phantom and with a 10 cm X 10 cm irradiation field. For fast neutron dose deposition the calculated and experimental curves have the same slope but different shape: only the experimental curve shows a maximum at 2.27 cm depth corresponding to the build-up. The difference is due to the Monte Carlo simulation which does not follow the secondary particles. Finally, a dose enhancement of, respectively, 4.6% and 10.4% are found for 10 cm X 10 cm or 20 cm X 20 cm fields, provided that 100 micrograms/g of 10B is loaded in the tissues. It is anticipated that this calculation method may be used to improve BNCE of fast neutron irradiations through collimation modifications.
快速中子辐照的硼中子俘获增强（BNCE）利用组织深处产生的热中子在肿瘤细胞内的10B上引发中子俘获反应。剂量增强与10B浓度以及在组织深处测量的热中子通量相关，在本文中我们展示了蒙特卡罗模拟用于研究BNCE剂量学的可行性。带电粒子FLUKA代码已用于计算铍靶的初级中子产额，而MCNP - 4A已用于这些中子在尼斯生物医学回旋加速器几何结构中的输运。已计算了有机玻璃模型深处的快中子能谱和剂量沉积、热通量和热中子能谱。热中子通量已与分别用校准的热释光剂量计（分别掺杂6Li或7Li的TLD - 600和TLD - 700）确定的实验结果进行了比较。理论结果与实验结果吻合良好：在模型4 cm深度且辐照场为10 cm×10 cm时，计算得到的热中子通量为10.3×10(6) n/cm2 s1，测量值为9.42×10(6) n/cm2 s1。对于快中子剂量沉积，计算曲线和实验曲线斜率相同但形状不同：只有实验曲线在对应积累的2.27 cm深度处出现最大值。差异是由于蒙特卡罗模拟未跟踪次级粒子。最后，当组织中加载100微克/克的10B时，对于10 cm×10 cm或20 cm×20 cm的场，分别发现剂量增强为4.6%和10.4%。预计这种计算方法可用于通过准直修改来改善快速中子辐照的BNCE。
