Risk of hematologic cancers from repeated low-dose diagnostic radiation

描述（由申请人提供）：大部分美国人口通过职业暴露或背景电离辐射接触小剂量电离辐射。最近，一个额外的和不断增加的辐射照射源来自医疗诊断辐射检查，如X射线和计算机断层扫描（CT）。虽然高剂量电离辐射导致白血病的风险是众所周知的，但其他血液系统癌症，如多发性骨髓瘤（MM）或非霍奇金淋巴瘤（NHL）的风险尚未得到充分了解。随着时间的推移，较低的辐射剂量也不会带来风险。我们建议通过汇集来自加拿大大型荧光透视队列研究的数据与来自马萨诸塞州的类似研究的数据来检查诊断X射线与血液学癌症结果之间的关联，该研究由美国国家癌症研究所（NCI）癌症流行病学和遗传学分部的放射流行病学分支进行。荧光透视是一种成像技术，使用X射线获得患者器官的实时移动图像。来自加拿大和NCI队列的患者在结核病治疗过程中接受了重复的X射线荧光镜检查。这两项研究在过去都没有检查过血液癌症的风险。在荧光透视研究（HemFluoro研究）的汇总分析中，这项血液学癌症辐射相关风险的拟定研究将纳入77，100例血液学癌症死亡率随访超过50年的患者。分析将基于222例白血病，70例多发性骨髓瘤和183例非霍奇金淋巴瘤，使其成为暴露于低剂量诊断电离辐射的人群中最大的血液癌症研究。研究结果将直接关系到美国人口暴露于CT扫描的风险预测，因为血液系统癌症和辐射暴露的背景率相似。研究样本将包括各种年龄的男性和女性，此外还将有大量关于可改变的风险因素的数据，如吸烟。对可改变的风险因素的评估是PAR-12-039公告中规定的四个关键研究领域之一。总体科学目标是扩大关于白血病、多发性骨髓瘤和非霍奇金淋巴瘤的辐射相关风险的现有知识，并填补在低剂量辐射照射下与辐射相关的致癌作用方面仍然存在的知识空白。这项研究的结果将刺激对不同人群血液系统癌症的进一步研究。本研究的公共卫生影响将是显著的，因为我们将评估当前公共辐射安全限值的适当性，这些限值主要基于暴露于高剂量电离辐射的受试者的研究。

DESCRIPTION (provided by applicant): A large proportion of the U.S. population comes into contact with small doses of ionizing radiation through occupational exposures or from background ionizing radiation. More recently, an additional and increasing source of radiation exposure is from medical diagnostic radiation examinations, such as X-rays and computed tomography (CT) scans. While the risk of leukemia from high doses of ionizing radiation are well known, the risk of other hematologic cancers, such as multiple myeloma (MM) or non-Hodgkin lymphoma (NHL), are not well understood. Neither are the risks from lower radiation doses that are protracted over time. We propose to examine the association between diagnostic X-rays and hematologic cancer outcomes by pooling the data from a large Canadian Fluoroscopy cohort study with data from a similar study in Massachusetts, conducted by the Radiation Epidemiology Branch of the Division of Cancer Epidemiology and Genetics, the National Cancer Institute (NCI). Fluoroscopy is an imaging technique that uses X-rays to obtain real-time moving images of patient's organs. Patients from the Canadian and NCI cohorts received repeated X-ray fluoroscopic examinations in the course of treatment for tuberculosis. Neither study has examined risks of hematologic cancers in the past. This proposed study of radiation-related risks of hematologic cancers in the pooled analysis of fluoroscopy studies (HemFluoro study) will include 77,100 patients with more than 50 years of follow up for mortality from hematologic cancers. Analyses will be based on 222 cases of leukemia, 70 cases of multiple myeloma and 183 cases of non-Hodgkin lymphoma, making it the largest study of hematologic cancers in a population exposed to low doses of diagnostic ionizing radiation. Study findings will be directly relevant for risk projections for the U.S. population exposed to CT scans because of similarity of background rates of hematologic cancers and of radiation exposures. The study sample will include men and women of a wide range of ages and additionally will have extensive data on modifiable risk factors, such as smoking. Evaluation of modifiable risk factors is one of the four key areas of research specified in the PAR-12-039 announcement. The overall scientific objective is to expand the existing body of knowledge on radiation-related risks of leukemia, MM and NHL and to address remaining gaps in knowledge with respect to radiation-related carcinogenesis at low-dose radiation exposures. Results from this study will stimulate further research on hematologic cancers in different populations. The public health impact of this study will be significant because we will assess the appropriateness of current public radiation safety limits, which are primarily based on the studies of subjects exposed to high doses of ionizing radiation.