Title: Thyroid Cancer study - Cumbrian Birth Cohort
Funder: Department of Health and Social Care

Abstract: Background: In 1957, a fire (the &ldquo;Windscale Fire&rdquo;) developed in a nuclear reactor at Sellafield, Cumbria, which led to uncontrolled releases of radionuclides to atmosphere. One of the most important radionuclides released was iodine-131 (half-life, 8 days), and the concentration of 131I in cow s milk was sufficiently high to warrant a milk distribution ban. Iodine-131 concentrates in the thyroid gland, and it is known that the thyroids of children are particularly sensitive to radiation-induced thyroid cancer. A limited number of measurements of thyroid doses received by children in the vicinity of Sellafield showed doses of typically 20-30 mGy, but one child had a thyroid dose of ~150 mGy, possibly because of drinking locally sourced milk. A recent geographical/temporal correlation study of thyroid cancer incidence in Cumbria and Lancashire showed patterns of incidence among those who were young in1957 that were difficult to interpret. Aims: To derive thyroid cancer incidence rates among those born in Cumbria who were children at the time of the Windscale Fire in areas with different levels of iodine-131 contamination. Thyroid cancer incidence rates will also be determined for the same areas for people born after the accident who would not have been exposed to iodine-131. Confidence intervals for rates will be calculated. Research Plan: The Cumbrian births database contains information on all births from 1950 onwards to mothers resident in Cumbria. These data include name, date of birth and maternal residential address at birth. Children born during 1950-1958 would have been most at risk of developing thyroid cancer as a result of exposure to 131I released during the Windscale accident. The radiation-induced excess risk of thyroid cancer persists for many years after exposure, probably over the remaining lifetime. Published contours of 131I contamination from the Fire using measurements made in 1957, enables the creation of three areas of Cumbria with different levels of 131I contamination, and births can be assigned to these areas using the births database. The Cumbrian births on the database can be linked to national cancer registries to identify those in the birth cohort who have been registered as having developed thyroid cancer. Two birth periods will be used to calculate sex- and age-adjusted incidence rates: 1950-1958, and 1959-1980 (and also 1959-1967) to include those people who were not exposed to iodine-131 from the Windscale accident. The second period is used to identify any differences in the background rates of thyroid cancer in the areas that could affect the interpretation of rates in the first period. Thyroid cancer cases will be included with a diagnosis date in the period from the start of registrations in 1971 to the latest date for which reliable thyroid cancer registration data are available &ndash; it will be important to have as long a follow-up period as possible because of the increase in thyroid cancer incidence rates with attained age (the radiation-induced excess risk of thyroid cancer having been found to depend upon the background risk). Team: The team is drawn from the universities of Newcastle, Manchester and Glasgow, and includes researchers with expertise and experience in epidemiology, statistics, radiation risk and exposure assessment. The research group has collaborated before on the geographical/temporal correlation study of thyroid cancer incidence in Cumbria and Lancashire. Potential Impact/influence: It has been assumed that iodine-131 released during the Windscale accident has caused thyroid cancers, but that these will not be detectable against background cases. Should this not be so, a serious underestimation of risk has occurred, which would need investigation. One important implication would be for emergency response, since a future reactor accident would likely result in the release of iodine-131.

Lay abstract: In October 1957, one of the nuclear reactors at Windscale Works at Sellafield, Cumbria, caught fire (sometimes called the &ldquo;Windscale Fire&rdquo;). The materials released into the air from the reactor chimney included radioactive iodine (&quot;iodine-131&quot;), which only exists for a few weeks and then is gone, but it is important to protect people from radioactive iodine when it is in the environment. Radioactive iodine was found in milk from farms near Sellafield after the fire, so this milk had to be thrown away. Radioactive iodine concentrates in the thyroid gland and this can cause thyroid cancer, possibly many years later. Young children are particularly at risk. The radiation measurements of thyroids made just after the accident showed that exposures were not high and that it was unlikely that more thyroid cancers than normal would be found. A quick look at thyroid cancer in Cumbria showed patterns that were not easy to understand, so a deeper study is planned. This study will look at thyroid cancer in people born in Cumbria from 1950 onwards, and will look at areas with different levels of contamination by radioactive iodine. Because thyroid cancer can develop many years after exposure to radioactive iodine, thyroid cancers will be looked for over as long a period as possible, wherever people may be living in Britain. People born in 1950-1958 will have been babies or young children (or in the womb) at the time of the fire, so if radioactive iodine is increasing their risk of thyroid cancer then this should be seen in the most contaminated area near Sellafield when compared to other areas. However, thyroid cancer is not just caused by radioactive iodine, so other influences need to be accounted for. One way of doing this is to look at thyroid cancer in people born in Cumbria after 1958, who will not have been exposed to radioactive iodine from the accident, and this will be done in this study. The study offers the best practicable opportunity to determine whether any extra thyroid cancers can be detected.

Research activity codes: 2.4 SURVEILLANCE AND DISTRIBUTION;2.2 FACTORS RELATING TO PHYSICAL ENVIRONMENT
Health categories: CANCER AND NEOPLASMS