Radiation Dose Reconstruction of the exposed population in the Marshall Island

从1946年到1958年，美国在太平洋中部的马歇尔群岛的比基尼环礁和埃尼威托克环礁进行了66次核武器试验。因此，许多马绍尔人有可能受到核试验放射性沉降物的影响。放射性尘埃包括高放射性铯和碘。马绍尔人通过消化系统和呼吸系统摄入这些放射性物质：体内辐射照射。放射性碘暴露是甲状腺癌的公认危险因素，因此我们从1993年开始对马绍尔群岛人口中甲状腺癌的发生进行跟踪研究。研究初期（即横断面）的初步结果如下：（i）在试验前出生的人中甲状腺癌的患病率高达1.5%，（ii）辐射照射剂量与甲状腺癌患病率之间可能存在剂量反应关系。除了相对较小的癌症病例外，由于当时的可用剂量估计值非常粗略，因此这种剂量-反应关系在统计学上不显著。在本研究中，我们进行了更详细的剂量重建，以获得更多的研究功效。进行了三种类型的剂量重建：（一）甲状腺剂量，基于1954年布拉沃试验中朗格拉普和乌蒂里克高度受照者的甲状腺剂量;（二）剂量，基于未考虑辐射率的每个环礁的残留放射性铯;（三）考虑辐射率。使用i型剂量估计值，在受照量超过50 cGy的人群中，甲状腺剂量与甲状腺癌患病率之间存在显著的剂量反应。将使用这些新的剂量重建评价甲状腺癌发病率。

From 1946 to 1958, 66 times of American nuclear weapons tests were conducted at Bikini and Enewetak atolls in the Marshall Islands, which located the mid-pacific. consequently, many of the Marshallese people potentially exposed to the radio-active fallout of the tests. The fallout included high level of radio-active Cesium and Iodine. These radio-active agents were taken by the Marshallese through their digestive and respiratory systems: internal radiation exposure. It was well established risk factor for the thyroid cancer to expose to radio-iodine, so that we started the follow-up study to the thyroid cancer occurrence among the Marshallese population from 1993. The preliminary results of initial phase of the study(i.e. cross sectional) were follows: (i) the prevalence of the thyroid cancer among the people who was born before the test was as high as 1.5%, (ii) there was possible dose-response relationship between the radiation exposure dose and the prevalence of thyroid cancer. In addition to relatively small cancer cases, since the available dose estimate at that time was very rough, this dose-response relationship would be not statistically significant. We conducted more detail dose reconstruction to get more study power in this study. Three types of dose reconstruction were performed: (i) thyroid dose based on those of highly exposed people of Rongelap and Utirik from the Bravo test in 1954, (ii) dose based on residual radioactive Cesium of each atoll NOT taken into account radiation rate, (iii) that taken into account radiation rate. Using dose estimates type i, there was significant dose-response between thyroid dose and thyroid cancer prevalence among people exposed more than 50 cGy. Thyroid cancer incidence will be evaluated using these new dose reconstructions.