用Geant4研究水中H-1、He-4、Li-7和C-12核的微剂量谱和RBE
Microdosimetry spectra and RBE of H-1, He-4, Li-7 and C-12 nuclei in water studied with Geant4
摘要：
采用基于Geant 4的重离子治疗蒙特卡罗模型（MCHIT），研究了射程相近（~160-180 mm）的H-1、He-4、Li-7和C-12束流在水中的辐射场。模拟无壁和有壁组织等效正比计数器（TEPC）放置在体模外部或内部的微剂量测定光谱，分别在NIRS（日本）和GSI（德国）进行实验。碎裂反应对微剂量谱的影响进行了研究He-4，Li-7和C-12，并评估了不同电荷的核碎片在体模中的各种TEPC位置的贡献。MCHIT很好地描述了在束轴上测量的微剂量谱，特别是在布拉格峰附近。然而，模拟的频谱壁TEPC远离光束轴被低估。相对生物有效性（RBE）的考虑光束估计使用修改后的微剂量动力学模型。计算表明，与在平台区的1-1.2的适度值相比，对于氦、锂和碳束，RBE在布拉格峰附近达到2.2-2.9。我们的研究结果表明，氦和锂束也是癌症治疗的有希望的选择。
英文摘要：
A Geant4-based Monte Carlo model for Heavy-Ion Therapy (MCHIT) is used to study radiation fields of H-1, He-4, Li-7 and C-12 beams with similar ranges (~160-180 mm) in water. Microdosimetry spectra are simulated for wall-less and walled Tissue Equivalent Proportional Counters (TEPCs) placed outside or inside a phantom, as in experiments performed, respectively, at NIRS, Japan and GSI, Germany. The impact of fragmentation reactions on microdosimetry spectra is investigated for He-4, Li-7 and C-12, and contributions from nuclear fragments of different charge are evaluated for various TEPC positions in the phantom. The microdosimetry spectra measured on the beam axis are well described by MCHIT, in particular, in the vicinity of the Bragg peak. However, the simulated spectra for the walled TEPC far from the beam axis are underestimated. Relative Biological Effectiveness (RBE) of the considered beams is estimated using a modified microdosimetric-kinetic model. Calculations show a similar rise of the RBE up to 2.2-2.9 close to the Bragg peak for helium, lithium and carbon beams compared to the modest values of 1-1.2 at the plateau region. Our results suggest that helium and lithium beams are also promising options for cancer therapy.
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