Results
After exclusion of 33 372 patients who could not be traced by NHSCR because of incomplete names or dates of birth in the RIS databases (and 960 non-UK resident patients) and those who were ineligible for follow-up because the exit date occurred less than 2 years in the case of leukaemia analyses or 5 years for brain tumours after the first scan (or when information, such as date of scan, was missing or obviously inaccurate), we included 178 604 individuals in the leukaemia analyses and 176 587 in the brain tumour analyses