Design

Population-based cohort study, linking data from national Medicare and Cancer Database records.

Setting

Australia.

Patients

10.9 million patients aged 0–19 years from 1985 to 2005. 681 211 patients had a Medicare-funded CT scan during the study period and were classed as exposed. Patients whose scans were in state-based tertiary hospitals (not Medicare funded) were not identifiable and were not moved to the exposed group.

3150 cancers were identified in patients who had a CT scan at least a year before the cancer was detected. Cancers detected within a year of the CT scan were not included to minimise the potential reverse causation of CT scans performed for cancer-related symptoms.

Risk factors

Time since exposure, year of exposure, age at exposure, sex, socioeconomic status, site of CT scan and …