gms | German Medical Science

Background: Exposure with computed tomographies (CT) in childhood was recently linked to increased cancer risk in two large epidemiological cohort studies from England and Australia and a smaller study from Taiwan. Uncertainty remains to which extent the risk may be driven by reverse causation or confounding by indication as the indications or results of the scans were not accessed.

Methods: We performed a nationwide cohort study to investigate cancer risk of children exposed to CT before the age of 15 in Germany. Cohort data were collected from large hospitals. Cancer cases were identified using the childhood cancer registry. For all cases and a random sample of non-cases the exams’ results and available medical files from the cancer registry were reviewed to assess the underlying medical conditions at the time of the CT. In the main analysis we calculated standardized incidence ratios (SIR) for all cancer sites combined, leukemia and CNS-tumours. In a sensitivity analysis, SIRs were calculated for different latency periods and specific sub cohorts. Individual dosimetry using the technical CT parameters is still underway.

Results: 50,865 of 82,971 children examined between 1983 and 2010 in the 20 participant hospitals fulfilled the inclusion criteria. 71 incident cancer cases were observed (latency 6 months). Among the cases with available medical information 26% (15) had prevalent cancer at time of first exposure. An additional 24% (14) were at high risk of developing a cancer due to the underlying medical conditions. No cancer was found in the reviewed reports of the control sample, while 4% (6) persons were judged at high risk of developing a cancer. After two years latency the SIR for leukemia was 1.72 (n= 12, 95% CI: 0.89 - 3.01), for CNS-tumours 1.35 (n= 7, 95% CI: 0.54 – 2.78) and for all cancer combined 1.87 (n= 39, 95% CI: 1.33 – 2.55). Longer latency resulted in reduced the SIR for all outcomes.

Conclusion: This is the first cohort study on cancer risk following pediatric CTs in Germany. However, the cohort is rather small and follow-up limited. As a unique feature, we were able to collect data on the medical conditions at exposure. The analysis of this information indicates that cancer risk after CT exposure has to be assessed with great caution and reverse caution may partly explain results from previous studies.