Cancer risk evaluation after radiation exposure from computed-tomography (CT) diagnostics during childhood (KiCT)
Description
- Modern radiation protection initiatives acknowledge and particularly discuss possible risks of increasing radiation exposure due to medical diagnostic imaging. To date however, there are few risk data/estimates available, especially for diagnostic procedures with relatively high individual radiation exposure such as computed tomography (CT) or nuclear medicine. The epidemiological cohort study investigates whether childhood exposure to ionizing radiation from computed tomography examinations leads to increased cancer incidence in children and adolescents.
Results:
Overall, 16 clinics were included in the main study of the 31 institutions contacted. A total of 82,971 individuals were registered. Of these 44.609 were included. That is, they were examined at least once with CTs until the age of 15, were not affected by cancer up to 2 years after the first known CT and lived in Germany at the time of the investigation. 38,362 patients did not meet at least one of these criteria and were excluded. On average, each cohort member was examined 1.6 times with CT in the observation period. The most frequently examined body region was the head with 65% of all CTs. For the calculation of the individual radiation exposure published reference values by Miglioretti et al. 2013 were used. The average estimated radiation doses of the included cohort members were 11.7 mGy bone marrow dose, 34.4 mGy brain dose, and 5.8 mGy colon dose.
Of the 44,609 individuals included, cancer was diagnosed in 46 children at the earliest 2 years after the first CT (cases). The findings and the medical information of the Children's Cancer Registry were analyzed from cases and a random selection of non-diseased individuals, if these were available. Among the cases with available information, 19% (n = 7) were diagnosed with cancer at the time of CT and 22% (n = 8) who were at higher risk of developing cancer (i.e., "individuals with increased risk"). The individuals who were already suffering from cancer at the time of CT were excluded from the analysis. Among the non-cases were 3.8% (n = 6) who were at increased risk of developing cancer and no person who had already had cancer. To determine cancer risk after exposure to ionizing radiation from CT examinations, the incidence of the cohort was compared with that of the same aged general population (standardized incidence rate (SIR) analysis). Using 2 year-latency, an SIR of 1.87 (95% CI: 1.33-2.55) was observed for all types of cancer. The SIR for leukemia was 1.72 (95% CI: 0.89 - 3.01) after 2 years of latency. After 5 years latency, only one CNS tumor was observed, the SIR was 0.45 (95% CI: 0.01-2.50). Based on three observed cases after 5 years latency, an increased risk of developing another solid tumor was observed (SIR = 1.42 (95% CI: 0.29 - 4.15)). For lymphomas, an increased risk was observed after 2 years of latency (SIR = 3.26 (95% CI: 1.63 - 5.83). However, the results of the subgroup and sensitivity analyzes suggest that this result is mainly due to confounding by indication. When "individuals with increased risk" and Hodgkin-Lymphoma cases were excluded from the risk analysis, the risks of developing lymphoma was significantly lower (SIR = 1.23 (95% CI: 0.34 - 3.15).
The analysis of possible dose-effect relationships found no positive association between the risk of cancer and the obtained colon dose after 2 years of latency. After five years of latency, no positive association could be found between the obtained brain dose in mGy and the risk of a CNS tumor. For leukemia, an increased HR per mGy bone marrow dose was obtained after 2 years of latency: HR = 1.009 (95% CI: 0.981-1.037). These results are consistent with the results of the SIR analyses, but lower than the risk estimates of the previously published cohort studies on cancer risk after exposure to CTs.
Funding period
- Begin: September 2010
End: December 2013
Sponsor
- Federal Ministry of Education and Research