中年辐射暴露与终生癌症风险的研究

一项详细的分析显示，与年轻时受到辐射的人相比，中年时受到辐射的成年人终生患癌症的风险基本不变。哥伦比亚大学医学中心发表在《国家癌症研究所杂志》网络版上的一项研究描述了这些发现。研究发现，一个50岁的人暴露在电离辐射下的癌症风险估计是早期估计的两倍，这一发现可能对x射线诊断测试和CT扫描具有实际意义，这些测试主要是在中年人身上进行的。这一发现对从事辐射工作的人也应该具有特别重要的意义，因为大多数受辐射影响的人通常也是中年人。哥伦比亚大学医学中心的副研究科学家Igor Shuryak博士和哥伦比亚大学内科和外科学院辐射生物物理学希金斯教授David J. Brenner说:“实际上，如果中年辐射暴露导致的终身癌症风险高于之前的估计，可能会产生相当大的社会后果。”“中年人常见的辐射照射来源是放射诊断。在过去的30年里，美国人暴露在医疗电离辐射下的人数增加了六倍，这主要是因为计算机断层成像技术的迅速发展。”到目前为止，传统观念认为，一个人受到辐射的年龄越大，患癌症的几率就越小。Shuryak和布伦纳。然而，对日本原子弹爆炸幸存者的长期研究提供了相反观点的统计证据，表明40岁以后受到辐射的人患辐射致癌的风险与成年早期受到辐射的人一样高。 Because these epidemiological findings were inconsistent with standard models of how radiation causes cancer, they had been widely overlooked, they said. To explore this issue, Dr. Brenner and Rainer Sachs at the University of California at Berkeley created a model of cancer risk assuming two different but well established pathways through which radiation exposure can ultimately lead to cancer. The first is initiation of gene mutations that convert normal stem cells to premalignant cells which could eventually lead to cancer; the second is radiation-induced promotion, or “expansion,” of the number of existing premalignant cells in the body. In their model, the initiation effect plays a greater role in children than in adults because cells initiated at an early age have a longer time available to expand in number and progress on the pathway to cancer. The promotion effect, on the other hand, is more important for radiation exposures in middle age, because the adult body already contains larger numbers of premalignant cells. The researchers first applied the model to the Japanese atomic bomb survivor data and were able to reproduce the cancer risk patterns associated with age at radiation exposure that were observed in the Japanese atomic bomb survivors. They then applied the same model to predict cancer risks as a function of age in a U.S. population captured in the latest National Academy of Sciences’ BEIR (Biological Effects of Ionizing Radiation) report. As with the Japanese atomic bomb survivors, the researchers found that the predicted cancer risks do not decrease with increasing age of exposure in the age range from about 30 to 60. “This finding is very different from current ‘best’ radiation risk estimates that predict sharply decreasing risks over this range of exposure ages,” Dr. Brenner says.