Epidemiological studies of natural sources of radiation and childhood cancer: current challenges and future perspectives

Abstract

Empirical estimation of cancer risks in children associated with low-dose ionizing radiation (<100 mSv) remains a challenge. The main reason is that the required combination of large sample sizes with accurate and comprehensive exposure assessment is difficult to achieve. An international scientific workshop "Childhood cancer and background radiation" organised by the Institute of Social and Preventive Medicine of the University of Bern brought together researchers in this field to evaluate how epidemiological studies on background radiation and childhood cancer can best improve understanding of the effects of low-dose ionising radiation. This review summarises and evaluates the findings of the existing studies in the light of their methodological differences, identifies key limitations and challenges and proposes ways forward. Large childhood cancer registries, such as those in Great Britain, France and Germany, now allow the conducting of studies that should have sufficient statistical power to detect the effects predicted by standard risk models. Nevertheless, larger studies or pooled studies will be needed to investigate disease subgroups. The main challenge is to accurately assess children's individual exposure to radiation from natural sources and from other sources, as well as potentially confounding non-radiation exposures, in such large study populations. For this, the study groups should learn from each other to improve exposure estimation and develop new ways to validate exposure models with personal dosimetry.

Risk Factors for Childhood Leukemia: Radiation and Beyond

“…By far the greatest contribution to exposure received by the general world population comes from natural background radiation (NBR) (98). Numerous epidemiological studies investigated the association of NBR exposure (including radon and gamma radiation exposure) and cancer risk (including CL), but results are mostly inconsistent (99). In a special workshop session dedicated to NBR, a recent study from Switzerland was discussed that used data from a census-based cohort study to check for an association between cancer in children <16 years of age and exposure to terrestrial gamma and cosmic radiation.…”

“…For a better estimation of indoor gamma ray dose rates, several ad hoc models were explored and the results were published (106)(107)(108). Some of the most recent studies have been summarized by Mazzei-Abba et al (99) in 2019 and their review includes a comprehensive discussion about methodological differences, limitations, and challenges that have to be faced when evaluating the findings of these studies. They point out that larger study populations or pooled studies are needed to investigate cytogenetic subgroups of diseases, while the main challenge is to accurately assess children's individual exposure to NBR.…”

Summary of Radiation Research Society Online 66th Annual Meeting, Symposium on “Epidemiology: Updates on epidemiological low dose studies,” including discussion

“…A number of national record-based studies of childhood cancer and natural background radiation have been undertaken. These have been reviewed by Mazzei-Abba et al (Mazzei-Abba et al 2020). Since that review further studies have been published by Berlivet et al (Berlivet et al 2020) and Nikkilä et al (Nikkilä et al 2020).…”

“…Results from these studies have been mixed. The results of five studies of childhood leukaemia and natural background radiation have been compared (Kendall et al 2020 submitted;Mazzei-Abba et al 2020). Two studies, from Britain (Kendall et al 2013) and from Switzerland (Spycher et al 2015) were positive and statistically significant.…”

Birth characteristics and childhood leukemia in Switzerland: a register-based case–control study

“…Established risk factors include ionizing radiation in medium to high doses and certain inherited disorders such as Li Fraumeni syndrome or chromosomal abnormalities such as Down syndrome, yet these account for only a fraction of cases [2,3]. Suspected environmental risk factors include low level ionizing radiation [4,5], air pollution [6], benzene [7], exposure to infections [8,9], agricultural pesticides [10,11], or parental occupational exposures [12,13]. There is compelling evidence that childhood leukemia originates early in life with initial genetic alterations occurring in utero or before conception [1,14].…”