Hunter Nezahat, Muirhead Colin R
Health Protection Agency, Radiation Protection Division, Oxford, UK.
J Radiol Prot. 2009 Mar;29(1):5-21. doi: 10.1088/0952-4746/29/1/R01. Epub 2009 Feb 18.
Information on Japanese A-bomb survivors exposed to gamma radiation has been used to estimate cancer risks for the whole range of photon (x-rays) and electron energies which are commonly encountered by radiation workers in the work place or by patients and workers in diagnostic radiology. However, there is some uncertainty regarding the radiation effectiveness of various low-linear energy transfer (low-LET) radiations (x-rays, gamma radiation and electrons). In this paper we review information on the effectiveness of low-LET radiations on the basis of epidemiological and in vitro radiobiological studies. Data from various experimental studies for chromosome aberrations and cell transformation in human lymphocytes and from epidemiological studies of the Japanese A-bomb survivors, patients medically exposed to radiation for diagnostic and therapeutic procedures, and occupational exposures of nuclear workers are considered. On the basis of in vitro cellular radiobiology, there is considerable evidence that the relative biological effectiveness (RBE) of high-energy low-LET radiation (gamma radiation, electrons) is less than that of low-energy low-LET radiation (x-rays, betas). This is a factor of about 3 to 4 for 29 kVp x-rays (e.g. as in diagnostic radiation exposures of the female breast) and for tritium beta-rays (encountered in parts of the nuclear industry) relative to Co-60 gamma radiation and 2-5 MeV gamma-rays (as received by the Japanese A-bomb survivors). In epidemiological studies, although for thyroid and breast cancer there appears to be a small tendency for the excess relative risks to decrease as the radiation energy increases for low-LET radiations, it is not statistically feasible to draw any conclusion regarding an underlying dependence of cancer risk on LET for the nominally low-LET radiations.
有关遭受伽马辐射的日本原子弹幸存者的信息，已被用于估算辐射工作人员在工作场所或诊断放射学中的患者及工作人员通常会遇到的整个光子（X射线）和电子能量范围内的癌症风险。然而，对于各种低线性能量传递（低LET）辐射（X射线、伽马辐射和电子）的辐射有效性存在一些不确定性。在本文中，我们基于流行病学和体外放射生物学研究，综述有关低LET辐射有效性的信息。考虑了来自各种关于人类淋巴细胞染色体畸变和细胞转化的实验研究的数据，以及来自日本原子弹幸存者、因诊断和治疗程序而接受医学辐射的患者以及核工业工作人员职业照射的流行病学研究的数据。基于体外细胞放射生物学，有大量证据表明，高能低LET辐射（伽马辐射、电子）的相对生物效能（RBE）低于低能低LET辐射（X射线、β射线）。对于29 kVp X射线（例如女性乳房的诊断辐射照射）和氚β射线（在核工业的某些部分会遇到），相对于钴-60伽马辐射和2 - 5 MeV伽马射线（日本原子弹幸存者所接受的），这一系数约为3至4。在流行病学研究中，尽管对于甲状腺癌和乳腺癌，低LET辐射的超额相对风险似乎有随着辐射能量增加而略有下降的趋势，但就名义上的低LET辐射而言，得出癌症风险对LET存在潜在依赖性的任何结论在统计学上并不可行。
