Abstract
Background Although CT scans are very useful clinically, potential cancer risks exist from associated ionising radiation, in particular for children who are more radiosensitive than adults. We aimed to assess the excess risk of leukaemia and brain tumours after CT scans in a cohort of children and young adults. Methods In our retrospective cohort study, we included patients without previous cancer diagnoses who were fi rst examined with CT in National Health Service (NHS) centres in England, Wales, or Scotland (Great Britain) between 1985 and 2002, when they were younger than 22 years of age. We obtained data for cancer incidence, mortality, and loss to follow-up from the NHS Central Registry from Jan 1, 1985, to Dec 31, 2008. We estimated absorbed brain and red bone marrow doses per CT scan in mGy and assessed excess incidence of leukaemia and brain tumours cancer with Poisson relative risk models. To avoid inclusion of CT scans related to cancer diagnosis, follow-up for leukaemia began 2 years after the fi rst CT and for brain tumours 5 years after the fi rst CT. Findings During follow-up, 74 of 178 604 patients were diagnosed with leukaemia and 135 of 176 587 patients were diagnosed with brain tumours. We noted a positive association between radiation dose from CT scans and leukaemia (excess relative risk [ERR] per mGy 0·036, 95% CI 0·005-0·120; p=0·0097) and brain tumours (0·023, 0·010-0·049; p<0·0001). Compared with patients who received a dose of less than 5 mGy, the relative risk of leukaemia for patients who received a cumulative dose of at least 30 mGy (mean dose 51·13 mGy) was 3·18 (95% CI 1·46-6·94) and the relative risk of brain cancer for patients who received a cumulative dose of 50-74 mGy (mean dose 60·42 mGy) was 2·82 (1·33-6·03). Interpretation Use of CT scans in children to deliver cumulative doses of about 50 mGy might almost triple the risk of leukaemia and doses of about 60 mGy might triple the risk of brain cancer. Because these cancers are relatively rare, the cumulative absolute risks are small: in the 10 years after the fi rst scan for patients younger than 10 years, one excess case of leukaemia and one excess case of brain tumour per 10 000 head CT scans is estimated to occur. Nevertheless, although clinical benefi ts should outweigh the small absolute risks, radiation doses from CT scans ought to be kept as low as possible and alternative procedures, which do not involve ionising radiation, should be considered if appropriate.
Original language | English |
---|---|
Pages (from-to) | 499-505 |
Number of pages | 7 |
Journal | The Lancet |
Volume | 380 |
Issue number | 9840 |
DOIs | |
Publication status | Published - Aug 2012 |
Bibliographical note
Funding Information:This study was supported by contract NO2-CP-75501 from the US National Cancer Institute and by the Radiation Research Programme of the UK Department of Health ( RRX119 ). We thank the North of England Children's Cancer Research Fund for their continued support of paediatric cancer epidemiology studies at Newcastle University (Newcastle upon Tyne, UK); the staff in radiology departments across Great Britain who contributed data; Richard Hardy, Katharine Kirton, and Wenhua Metcalf from Newcastle University; Jeremy Miller (Information Management Services, Rockville, MD, USA); and Martha Linet and Lindsay Morton from the National Cancer Institute (Bethesda, MD, USA) for their assistance. Elaine Ron, who was one of the original investigators for this study, died of cancer on Nov 20, 2010. We greatly appreciate her contributions, support, and devotion to this study and to the field of radiation epidemiology.