Diagnostic X-rays and risk of childhood leukaemia

Abstract

Background: The association between diagnostic X-ray exposures early in life and increased risk of childhood leukaemia remains unclear.

Methods: This case-control study included children aged 0-14 years diagnosed with acute lymphoid leukaemia (ALL, n = 711) or acute myeloid leukaemia (AML, n = 116) from 1995 to 2008. Controls were randomly selected from the California birth registry and individually matched to cases with respect to date of birth, sex, Hispanic ethnicity and maternal race. Conditional logistic regression analyses were performed to assess whether ALL or AML was associated with self-reported child's X-rays after birth (post-natal), including number of X-rays, region of the body X-rayed and age at first X-ray, as well as maternal X-rays before and during pregnancy (preconception and prenatal).

Results: After excluding X-rays in the year prior to diagnosis (reference date for matched controls), risk of ALL was elevated in children exposed to three or more post-natal X-rays [odds ratio (OR) = 1.85, 95% confidence interval (CI) 1.12-2.79]. For B-cell ALL specifically, any exposure (one or more X-rays) conferred increased risk (OR = 1.40, 95% CI 1.06-1.86). Region of the body exposed was not an independent risk factor in multivariable analyses. No associations were observed between number of post-natal X-rays and AML (OR = 1.05, 95% CI 0.90-1.22) or T-cell ALL (OR = 0.84, 95% CI 0.59-1.19). Prevalence of exposure to prenatal and preconception X-rays was low, and no associations with ALL or AML were observed.

Conclusions: The results suggest that exposure to post-natal diagnostic X-rays is associated with increased risk of childhood ALL, specifically B-cell ALL, but not AML or T-cell ALL. Given the imprecise measures of self-reported X-ray exposure, the results of this analysis should be interpreted with caution and warrant further investigation.

Figure 1

Selection of controls for the NCCLS from August 1995 to July 2008. In instances when first-choice controls were not available, i.e. they refused, were ineligible or could not be located, alternative controls were selected (indicated with shading in the flow diagram). If controls refused participation after enrolment or were later found to be ineligible, additional controls were not identified (n = 26, or 2% of enrolled subjects)

Figure 2

Exposure to post-natal diagnostic X-rays and risk of ALL; ORs and 95% CIs for different length of exclusionary period

Figure 3

ORs and 95% CIs for ever X-ray exposure, by region of the body exposed for the following, mutually exclusive, combinations of exposure: (i) chest only; (ii) broken bone only; (iii) skull only; (iv) ‘other’ only; (v) multiple regions exposed, including chest and (vi) multiple regions exposed, not including chest. The estimates are for ever exposure, not for numbers of X-rays, e.g. ‘chest only’ includes all subjects who received at least one chest X-ray and no other types of X-rays