Nineteen case-control (n=17,725) and six cohort studies (n=approximately 49,000 with 134 diagnosed cancers) were included.
Case-control studies: Nine studies assessed the effect of prenatal X-rays on leukaemia and found no association (pooled OR 0.99, 95% CI 0.87 to 1.13) and little heterogeneity between studies (I2=0%). The funnel plot indicated some evidence of publication bias. There was no association observed between prenatal X-rays and solid tumours (three studies), central nervous system tumours (four studies) and non-Hodgkin lymphoma (three studies). Four studies reported inconsistent results for postnatal X-rays and leukaemia (two significantly increased odds, one significantly decreased and one no association). There was no association observed between postnatal X-rays and solid tumours (three studies), central nervous system tumours (four studies) and non-Hodgkin lymphoma (two studies).
Cohort studies: One study assessed prenatal X-rays and childhood cancer and found a significantly reduced risk (SIR 0.7, 95% CI 0.5 to 0.9). One study found no association between postnatal X-rays and cancer risk, but one reported an increase in risk over all cancer sites (SIR 2.3, 95% CI 1.2 to 4.1). Two studies found no association between postnatal use of diagnostic iodine-131 and risk of thyroid cancer. One large study found an increased risk of breast cancer after postnatal X-rays for scoliosis diagnostics in girls (SMR 1.7, 95% CI 1.3 to 2.1), but no association with leukaemia.