Second follow-up of a German cohort on childhood cancer incidence after exposure to postnatal diagnostic x-ray

Abstract

Studies on children exposed to ionizing radiation by computed tomography (CT) indicate an increased risk of leukemia and central nervous system (CNS) tumors. Evidence of the risks associated with diagnostic X-ray examinations, the most frequent examination in pediatric radiology, in which the radiation dose is up to 750 times lower compared to CT examinations, is less clear. This study presents results of the second follow-up for the risk of childhood cancer in a cohort of children (<15 years) with diagnostic X-ray exposure at a large German hospital during 1976-2003 followed for additional 10 years until 2016. With a latency period of 6 months, 92,998 children contributed 794,549 person-years. The median effective dose was 7 μSv. 100 incident cancer cases were identified: 35 leukemia, 13 lymphomas, 12 CNS tumors, 15 blastomas, 15 sarcomas and 10 other solid tumors, consisting of six germ cells tumors, three thyroid cancers and one adrenocortical carcinoma. For all cancer cases combined the standardized incidence ratio (SIR) was 1.14 (95% confidence interval (CI) 0.93-1.39), for leukemia 1.15 (95% CI 0.63-1.61), for lymphomas 1.03 (95% CI 0.55-1.76), for CNS tumors 0.65 (95% CI 0.34-1.14), for blastomas 1.77 (95% CI 0.91-2.91), for sarcomas 1.28 (95% CI 0.71-2.11) and for other solid tumors 2.38 (95% CI 1.14-4.38). Dose-response analysis using Poisson regression revealed no significant trend for dose groups. Results did not differ substantially with a latency period of 2 years for all cancer entities and 5 years for solid tumors in sensitivity analyses. Overall, the null results of the first follow-up were confirmed. Although an association between radiation exposure and a risk for certain solid tumors like thyroid cancer is known, the significantly increased SIR in the group of other solid tumors must be critically interpreted in the context of the small number of cases and the very low doses of radiation exposure in this group.

Risk Factors for Childhood Leukemia: Radiation and Beyond

“…A recent study of six pooled studies assessing cancer risks associated with computed tomography (CT) with available ABM between 5.9 and 10.1 mGy found a significant increased risk for CL (95). To date, no increased risk was found for single X-ray examinations (95,96).…”

Cancer risks among studies of medical diagnostic radiation exposure in early life without quantitative estimates of dose

“…Milne et al (Milne et al, 2014) also evaluated lag periods between 6 months and 5 years in relation to all radiological procedures, but little difference in brain tumour risk was observed. Reverse causation and confounding by indication are general problems in studies of diagnostic radiation exposure; only a few of the studies of other types of postnatal exposure assembled here deal with this by use of lag periods (Ager et al, 1965;Baaken et al, 2019;Bartley et al, 2010;Graham et al, 1966;Howe et al, 1989;Meinert et al, 1999;Preston-Martin et al, 1982;Rajaraman et al, 2011;Schuz et al, 2001;Shu et al, 2002), even to the limited extent that is attempted by Tettamanti et al (Tettamanti et al, 2017), Hong et al (Hong et al, 2019), Li et al (Li et al, 2020), Bailey et al (Bailey et al, 2010) and Milne et al (Milne et al, 2014) (see Table 2). Hence, one cannot discount the possibility that the relatively modest increases we have seen for postnatal exposures may largely result from such biases, and in this respect it is of interest that in the CT scan study of Hong et al (Hong et al, 2019), of the many different types of cancer investigated, the RR (with a lag of 2 years) was <1.0 only for lymphoid leukaemia while the RR estimates were >1.0 for all other types of cancer, some significantly so (e.g., digestive and respiratory cancers and NHL) and others not.…”

Reply to ‘Comment on: Baaken D, Hammer GP, Seidenbusch MC, Schneider K, Spix C, Blettner M, Pokora R and Lorenz E 2019 Second follow-up of a German cohort on childhood cancer after exposure to postnatal diagnostic x-ray J. Radiol. Prot. 39 1074–91’

“…We welcome the comments by Schmitz-Feuerhake on our study on childhood cancer after exposure to postnatal diagnostic x-ray [1] and the opportunity to explain some points in more detail.…”