Schmid E, Wagner F M, Romm H, Walsh L, Roos H
Radiobiological Institute, University of Munich, Schillerstrasse 42, 80336, Munich, Germany.
Radiat Environ Biophys. 2009 Feb;48(1):67-75. doi: 10.1007/s00411-008-0202-z. Epub 2008 Nov 1.
The biological effectiveness of neutrons from the neutron therapy facility MEDAPP (mean neutron energy 1.9 MeV) at the new research reactor FRM II at Garching, Germany, has been analyzed, at different depths in a polyethylene phantom. Whole blood samples were exposed to the MEDAPP beam in special irradiation chambers to total doses of 0.14-3.52 Gy at 2-cm depth, and 0.18-3.04 Gy at 6-cm depth of the phantom. The neutron and gamma-ray absorbed dose rates were measured to be 0.55 Gy min(-1) and 0.27 Gy min(-1) at 2-cm depth, while they were 0.28 and 0.25 Gy min(-1) at 6-cm depth. Although the irradiation conditions at the MEDAPP beam and the RENT beam of the former FRM I research reactor were not identical, neutrons from both facilities gave a similar linear-quadratic dose-response relationship for dicentric chromosomes at a depth of 2 cm. Different dose-response curves for dicentrics were obtained for the MEDAPP beam at 2 and 6 cm depth, suggesting a significantly lower biological effectiveness of the radiation with increasing depth. No obvious differences in the dose-response curves for dicentric chromosomes estimated under interactive or additive prediction between neutrons or gamma-rays and the experimentally obtained dose-response curves could be determined. Relative to (60)Co gamma-rays, the values for the relative biological effectiveness at the MEDAPP beam decrease from 5.9 at 0.14 Gy to 1.6 at 3.52 Gy at 2-cm depth, and from 4.1 at 0.18 Gy to 1.5 at 3.04 Gy at 6-cm depth. Using the best possible conditions of consistency, i.e., using blood samples from the same donor and the same measurement techniques for about two decades, avoiding the inter-individual variations in sensitivity or the differences in methodology usually associated with inter-laboratory comparisons, a linear-quadratic dose-response relationship for the mixed neutron and gamma-ray MEDAPP field as well as for its fission neutron part was obtained. Therefore, the debate on whether the fission-neutron induced yield of dicentric chromosomes increases linearly with dose remains open.
德国加兴新的研究反应堆FRM II的中子治疗设施MEDAPP（平均中子能量1.9 MeV）产生的中子在聚乙烯模体不同深度处的生物学效应已得到分析。全血样本在特殊照射室中接受MEDAPP束流照射，在模体2 cm深度处的总剂量为0.14 - 3.52 Gy，在6 cm深度处为0.18 - 3.04 Gy。测得在2 cm深度处中子和γ射线的吸收剂量率分别为0.55 Gy min⁻¹和0.27 Gy min⁻¹，而在6 cm深度处分别为0.28和0.25 Gy min⁻¹。尽管MEDAPP束流和前FRM I研究反应堆的RENT束流的照射条件并不相同，但两个设施产生的中子在2 cm深度处对于双着丝粒染色体给出了相似的线性二次剂量响应关系。对于MEDAPP束流，在2 cm和6 cm深度处获得了不同的双着丝粒剂量响应曲线，这表明随着深度增加，辐射的生物学效应显著降低。在中子或γ射线与实验获得的剂量响应曲线之间的交互或相加预测下，估计的双着丝粒染色体剂量响应曲线没有明显差异。相对于⁶⁰Co γ射线，MEDAPP束流在2 cm深度处的相对生物学效应值从0.14 Gy时的5.9降至3.52 Gy时的1.6，在6 cm深度处从0.18 Gy时的4.1降至3.04 Gy时的1.5。使用尽可能一致的最佳条件，即使用同一供体的血样和相同的测量技术约二十年，避免个体敏感性差异或通常与实验室间比较相关的方法学差异，获得了混合中子和γ射线MEDAPP场及其裂变中子部分的线性二次剂量响应关系。因此，关于裂变中子诱导的双着丝粒染色体产额是否随剂量线性增加的争论仍然悬而未决。
