Relationship between paediatric CT scans and subsequent risk of leukaemia and brain tumours: assessment of the impact of underlying conditions

Abstract

Background:We previously reported evidence of a dose–response relationship between ionising-radiation exposure from paediatric computed tomography (CT) scans and the risk of leukaemia and brain tumours in a large UK cohort. Underlying unreported conditions could have introduced bias into these findings.Methods:We collected and reviewed additional clinical information from radiology information systems (RIS) databases, underlying cause of death and pathology reports. We conducted sensitivity analyses excluding participants with cancer-predisposing conditions or previous unreported cancers and compared the dose–response analyses with our original results.Results:We obtained information from the RIS and death certificates for about 40% of the cohort (n∼180 000) and found cancer-predisposing conditions in 4 out of 74 leukaemia/myelodysplastic syndrome (MDS) cases and 13 out of 135 brain tumour cases. As these conditions were unrelated to CT exposure, exclusion of these participants did not alter the dose–response relationships. We found evidence of previous unreported cancers in 2 leukaemia/MDS cases, 7 brain tumour cases and 232 in non-cases. These previous cancers were related to increased number of CTs. Exclusion of these cancers reduced the excess relative risk per mGy by 15% from 0.036 to 0.033 for leukaemia/MDS (P-trend=0.02) and by 30% from 0.023 to 0.016 (P-trend<0.0001) for brain tumours. When we included pathology reports we had additional clinical information for 90% of the cases. Additional exclusions from these reports further reduced the risk estimates, but this sensitivity analysis may have underestimated risks as reports were only available for cases.Conclusions:Although there was evidence of some bias in our original risk estimates, re-analysis of the cohort with additional clinical data still showed an increased cancer risk after low-dose radiation exposure from CT scans in young patients.

Integration of a radiation biomarker into modeling of thyroid carcinogenesis and post-Chernobyl risk assessment

“…Application for diagnostic or therapeutic purposes can cause diseases such as leukemia or solid cancers of the brain, breast or thyroid even decades after exposure (1–3). Strongest evidence for the statistical association between radiation exposure and thyroid cancer has been produced by studies of children and adolescents who ingested radio-iodine from fallout of the Chernobyl accident in April 1986.…”

Projected cancer risks potentially related to past, current, and future practices in paediatric CT in the United Kingdom, 1990–2020

“…RadRAT incorporates an extended list of cancer site-specific risk models that were previously derived by the US National Research Council in the BEIR VII report (NRC, 2006) from cohorts of survivors of the Hiroshima and Nagasaki atomic bombings and patients receiving radiotherapy for benign diseases or repeated diagnostic procedures. The above-mentioned recent studies on CT exposures cannot provide a full picture of radiation-related risks, mainly because their duration of follow-up is still too short to describe cancer incidence after the age of 50 years (Pearce et al , 2012; Mathews et al , 2013; Huang et al , 2014; Berrington de Gonzalez et al , 2016; Journy et al , 2016). In consequence, most of these studies estimated risks for a limited range of cancer sites.…”

“…Since then, direct evidence of increased cancer risks after CT scans received in childhood or early adulthood has been provided in epidemiological studies (Pearce et al , 2012; Mathews et al , 2013; Huang et al , 2014; Journy et al , 2016), although there were uncertainties in the dose estimates and a possibility of bias owing to underlying medical conditions (Walsh et al , 2014; Berrington de Gonzalez et al , 2016). These studies have enhanced awareness about potential risks of X-ray exposures among the medical community and, along with considerable technological progress in CT, has led to further radiation dose optimisation in paediatrics.…”

Pediatric Exposures to Ionizing Radiation: Carcinogenic Considerations

“…This allowed the authors to exclude cases where cancer was present before the initial CT scan or who underwent CT scanning for a cause linked to a later cancer diagnosis. At least two recent studies have adopted this methodological approach and were still able to identify an increased risk associated with CT scans in childhood, albeit smaller than in the studies that did not [84,85]. One of these studies re-analyzed the data from Pearce and colleagues and found a more modest, yet still significant increase in cancer risk [85]; this raises doubts about possible additional biases in the experimental design of all epidemiological studies on the topic [86,87,88].…”