Schmid E, Panzer W, Schlattl H, Eder H
Institute for Cell Biology, University of Munich, Schillerstrasse 42, 80336 München, Germany.
J Radiol Prot. 2012 Sep;32(3):N129-39. doi: 10.1088/0952-4746/32/3/N129. Epub 2012 Jul 19.
The aim of this study was to investigate the effectiveness of different shielding materials in protective clothing using dicentric frequency in human peripheral lymphocytes as a marker of radiation-induced damage. Blood samples from a healthy donor were exposed to 70 kV x-rays behind shielding materials lead (Pb), tin/antimony (Sn + Sb) and bismuth barrier/tin/tungsten (Bi + Sn + W) with the same nominal lead equivalent value of 0.35 mm lead. Irradiation was performed either in contact (exposure position A, containing secondary radiation) or at a distance of 19 cm behind the shielding materials (exposure position B, containing only the unaffected transmitted photons). Using shielding material Sn + Sb, a significantly higher dicentric yield was determined at exposure position A relative to position B, whereas no significant differences were found between the exposure positions using shielding materials Pb or Bi + Sn + W. For doses up to 434.4 mGy at exposure position A, the slopes of the linear dose-response curves for dicentrics obtained behind shielding materials Pb and Bi + Sn + W were not significantly different, whereas a significantly higher slope was determined behind Sn + Sb relative to Pb and Bi + Sn + W. Using moderately filtered 220 kV x-rays as a reference, maximum RBE values at low doses (RBE(M)) of 1.22 ± 0.10, 2.28 ± 0.19 and 1.03 ± 0.12 were estimated immediately behind shielding materials Pb, Sn + Sb and Bi + Sn + W, respectively. These findings indicate a significantly higher RBE(M) of 70 kV x-rays behind shielding material Sn + Sb with respect to Pb or Bi + Sn + W. Using previous dicentric data obtained for exposure of blood from the same donor to x-rays at energies lower than 70 kV, it can be assumed that the increased RBE(M) of the broad spectrum of 70 kV x-rays (mean energy of 44.1 keV) may be attributed predominately to secondary (mainly fluorescence) radiation generated in the shielding material Sn + Sb that is able to leave the shielding material. Even if it is uncertain whether the marked dependency of the RBE at low doses on photon energy for chromosome aberrations is also representative for late radiation effects in healthy subjects, it should be taken into account that several prospective cohort studies have shown positive associations between higher chromosome aberrations in lymphocytes of healthy subjects and increased cancer incidence. Thus, it can be concluded that any additional biological damage by radiation exposure of healthy subjects, e.g. by using certain non-lead based shielding materials of protective clothing, should be avoided.
本研究的目的是使用人外周血淋巴细胞中的双着丝粒频率作为辐射诱导损伤的标志物，来研究防护服中不同屏蔽材料的有效性。将来自一名健康供体的血样置于屏蔽材料铅（Pb）、锡/锑（Sn + Sb）和铋屏障/锡/钨（Bi + Sn + W）后，接受70 kV的X射线照射，这些屏蔽材料的标称铅当量值均为0.35 mm铅。照射在接触条件下进行（暴露位置A，包含二次辐射），或在屏蔽材料后方19 cm处进行（暴露位置B，仅包含未受影响的透射光子）。使用屏蔽材料Sn + Sb时，暴露位置A处测定的双着丝粒产率相对于位置B显著更高，而使用屏蔽材料Pb或Bi + Sn + W时，暴露位置之间未发现显著差异。在暴露位置A，对于高达434.4 mGy的剂量，在屏蔽材料Pb和Bi + Sn + W后获得的双着丝粒线性剂量响应曲线的斜率无显著差异，而相对于Pb和Bi + Sn + W，在Sn + Sb后测定的斜率显著更高。以适度过滤的220 kV X射线作为参考，在屏蔽材料Pb、Sn + Sb和Bi + Sn + W后立即估计出低剂量（RBE(M)）下的最大RBE值分别为1.22±0.10、2.28±0.19和1.03±0.12。这些发现表明，相对于Pb或Bi + Sn + W，屏蔽材料Sn + Sb后的70 kV X射线的RBE(M)显著更高。利用先前获得的同一供体血液在低于70 kV能量下接受X射线照射的双着丝粒数据，可以假设70 kV宽谱X射线（平均能量为44.1 keV）增加的RBE(M)可能主要归因于屏蔽材料Sn + Sb中产生的能够离开屏蔽材料的二次（主要是荧光）辐射。即使尚不确定低剂量下RBE对染色体畸变光子能量的显著依赖性是否也代表健康受试者的晚期辐射效应，但应考虑到多项前瞻性队列研究表明，健康受试者淋巴细胞中较高的染色体畸变与癌症发病率增加之间存在正相关。因此，可以得出结论，应避免健康受试者因辐射暴露（例如使用某些非铅基防护服屏蔽材料）而造成的任何额外生物损伤。
