Occupational exposure to ionising radiation and central nervous system tumour mortality: a pooled analysis of Korean, French and US medical radiation workers.

BACKGROUND: High-dose ionising radiation (IR) is the only established modifiable risk factor for central nervous system (CNS) tumours, but the association with low- to moderate-dose IR is unclear. METHODS: The BECOME (Brain cancEr risk in joint COhort of MEdical workers exposed to ionizing radiation) study includes harmonised data from nested case-control studies of US, Korean and French medical radiation worker cohorts employed during 1926-2021. A total of 361 CNS tumour deaths were matched on sex, year of birth and cohort to 1851 controls alive at the time of death of the corresponding case. Badge doses, defined as Hp(10) (individual dose equivalent at 10 mm depth in tissue) and brain doses, were estimated using comparable protocols, and we evaluated age at first exposure, exposure duration and cumulative and annual mean doses (accounting for a 5-year lag). Conditional logistic regression also adjusted for number of years of education, duration of follow-up, exposure duration and age at first exposure. RESULTS: Cumulative brain dose averages were 10.5 (±13) mGy and 9.8 (±12.5) mGy for cases and controls, respectively. Overall, cumulative brain dose was not associated with CNS tumour death (OR=1.05; 95% CI 0.93 to 1.18 for a 10-mGy increase in cumulative brain dose) in all workers nor when the analysis was restricted to radiological technologists. A borderline significant dose-response association was found between occupational exposure to IR and CNS tumour death in medical workers first exposed after 1970 (OR=1.19; 95% CI 1.00 to 1.42 for a 10-mGy increase in cumulative brain dose). CONCLUSION: In this pooled nested case-control study, cumulative brain occupational radiation exposure was not associated with CNS mortality overall. More studies are needed of workers first exposed after 1970 and those conducting fluoroscopically guided interventional and nuclear medicine procedures.