Background:
With more than 500,000 computed tomography (CT) scans per year, Israel is one of the leading countries in CT use per capita. Radiation doses from these scans are substantially greater than from conventional X-rays and are in the range for which increased cancer risks have been shown. Pediatric CT scans are of particular concern because in comparison with adults, children are exposed to higher doses, they are generally more sensitive to the carcinogenic effects of radiation, and they have a longer life-span to express radiation-related cancer. In June 2006, the National Cancer Institute (NCI) and International Agency for Research on Cancer (IARC) initiated a first international meeting of researchers to develop a shared protocol for the first international study to determine whether the risk of developing cancer is increased in children undergoing CT scans.
Hypothesis:
The proposed study will be the first to collect empirical data on pediatric CT and cancer in Israel. The proposed study also provides a unique opportunity to provide valuable data as part of a very large international study aimed to provide direct, quantified estimates of the cancer risk associated with exposure to CT scans at a young age.
Rationale:
Due to the relatively recent widespread introduction of CT scans into common clinical practice, and the considerable latency period between radiation exposure and the development of cancers, the potential adverse health effects of CT scan exposure have not yet been directly studied. Although excess cancer risk to an individual from CT scanning is likely to be small given that radiation doses are usually relatively low, from a public health perspective, the large number of people exposed annually means that even small individual risks could result in a considerable number of excess cancer cases.
Methods:
The proposed study will have two phases. First, we plan to conduct a retrospective follow-up study of a cohort of 80,000 children under the age of 18 years who underwent CT scanning between 1985 and 1995 in community settings (Maccabi Healthcare Services, MHS) or pediatric hospital (Schneider Children's Medical Center of Israel, SCMCI). Cancer incidence will be evaluated in the study cohort in relation to exposure to CT scans. In phase II we will conduct a nested case-control study of leukemia to assess dose-response more precisely by using estimates of bone marrow dose for individual CT scans. This two-phase approach will allow us to restrict collection of detailed radiation exposure information to a small subgroup of the cohort. |