The link between radiation exposure and cancer first became evident in studies of survivors of the atomic bombings of Hiroshima and Nagasaki in 1945. Later studies established a link between therapeutic radiotherapy for cancer and increased risk of a second subsequent malignancy. There have, however, been few large, comprehensive studies to date of the association between the lower radiation levels associated with diagnostic testing and subsequent cancer risk.

Testicular cancer is one of the most treatable solid tumours, but survivors of this disease need regular monitoring for recurrence, generally through repeated X-ray computer tomography (CT) scans.

A typical regimen of 13 scans at increasing intervals over five years will expose a survivor to an approximate radiation dose of 260 milliSieverts (mSv). Carl van Walraven from the University of Ottawa, Ottawa, Ontario, Canada and his co-workers have now evaluated the risk of developing secondary malignancies in a large cohort of men in Ontario diagnosed with, and recovering from, testicular cancer.

Van Walraven and his colleagues identified all men diagnosed with testicular cancer in Ontario between 1991 and 2004 in records from the Ontario Cancer Registry. Records from patients who were diagnosed under the age of 18, who had previous malignancies, or who received radiotherapy were excluded from the study cohort.

As cancers are known to take a minimum of five years to develop following radiation exposure, all patients who received a second cancer diagnosis or died within five years of developing their testicular cancer were also excluded from the study. The resulting study population included 2,569 men with a mean age at diagnosis of 34.7 years, and who were observed for a median time of 11.2 years.

The researchers identified the type and date of each diagnostic procedure involving radiation for each study participant, and, where possible, estimated the total radiation dose received by his abdominal and pelvic region from this data.

Most of the tests recorded were CT scans; 97.8% of participants received at least one CT scan within the five years after the initial cancer diagnosis. The median dose was calculated to be 110 mSv, with a large range from 0 to 446 mSv. All subsequent abdominal and pelvic tumours diagnosed in this cohort (and, therefore, at least five years after the initial diagnosis) were recorded.

A total of fourteen men developed second malignancies of the abdominal-pelvic region during the study period; most of these were colorectal or kidney cancers. There was no significant difference in mean radiation dose in the five years after the first cancer diagnosis between these and the rest of the study population. There was also no significant association between radiation exposure and the time to development of the second tumour (hazard ratio per dose increase of 10 mSv, 0.99; 95% confidence interval 0.95-1.04).

The median dose of radiation received by these testicular cancer patients is higher than that received by many survivors of the Hiroshima and Nagasaki bombs.

Concern about the carcinogenic effects of this radiation is, therefore, valid. However, Van Walraven and his co-workers concluded from this study that the risk of developing a second abdominal-pelvic cancer following recovery from testicular cancer and its associated diagnostic radiation is very low. Moreover, the magnitude of this risk does not appear to be associated with the dose of radiation received, at least within the observed dose range.

Reference: 

van Walraven, C., Fergusson, D., Earle, C., Baxter, N., Alibhai, S., MacDonald, B., Forster, A.J. and Cagiannos, I. (2011). Association of Diagnostic Radiation Exposure and Second Abdominal-Pelvic Malignancies After Testicular Cancer. J. Clin. Oncol. 29(21), 2883-2888. DOI: 10.1200/JCO.2011.34.6379