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Pearce MS, Salotti JA, Little MP, et al .Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study

Institute of Health and Society, Newcastle University, Sir James Spence Institute, Royal Victoria Infirmary, Newcastle upon Tyne, UK.
The Lancet (Impact Factor: 45.22). 06/2012; 380(9840):499-505. DOI: 10.1016/S0140-6736(12)60815-0
Source: PubMed

ABSTRACT 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.
In our retrospective cohort study, we included patients without previous cancer diagnoses who were first 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 first CT and for brain tumours 5 years after the first CT.
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).
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 first 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 benefits 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.
US National Cancer Institute and UK Department of Health.

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    • "Concomitantly, the increased sensitivity of children and adolescents to IR might potentiate and reveal more clearly the eff ects of IR at low doses than in adults. Recently a number of studies were published dealing with the long-term risk of radiation-induced cancer following CT scans in childhood (Pearce et al. 2012, Mathews et al. 2013, Huang et al. 2014). "
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    ABSTRACT: A feasibility study on the application of the γ-H2AX foci assay as an exposure biomarker in a prospective multicentre paediatric radiology setting. A set of in vitro experiments was performed to evaluate technical hurdles related to biological sample collection in a paediatric radiology setting (small blood sample volume), processing and storing of blood samples (effect of storing blood at 4°C), the reliability of foci scoring for low-doses (merge γ-H2AX/53BP1 scoring), as well as the impact of contrast agent administration as potential confounding factor. Given the exploratory nature of this study and the ethical constraints related to paediatric blood sampling, blood samples from adult volunteers were used for these experiments. In order to test the feasibility of pooling the γ-H2AX data when different centres are involved in an international multicentre study, two intercomparison studies in the low-dose range (10-500 mGy) were performed. Determination of the number of x-ray induced γ-H2AX foci is feasible with one 2 ml blood sample pre- and post- computed tomography (CT) scan. Lymphocyte isolation and fixation on slides is necessary within 5h of blood sampling to guarantee reliable results. The possible enhancement effect of contrast medium on the induction of DNA DSB in a patient study can be ruled out if radiation doses and the contrast agent concentration are within diagnostic ranges. The intercomparison studies using in vitro irradiated blood samples showed that the participating laboratories, executing successfully the γ-H2AX foci assay in lymphocytes, were able to rank blind samples in order of lowest to highest radiation dose based on mean foci/cell counts. The dose response of all intercomparison data shows that a dose point of 10 mGy could be distinguished from the sham irradiated control (p = 0.006). The results demonstrate that it is feasible to apply the γ-H2AX foci assay as a cellular biomarker of exposure in a multicentre prospective study in paediatric CT imaging after validating it in an in vivo international pilot study on paediatric patients.
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    • "Computed tomography (CT) is an important imaging procedure, but the radiation dose required is relatively high compared to conventional radiographic procedures. Therefore radiation protection should be optimised to minimise risks of adverse health effects (Brenner and Hall 2007, Smith-Bindman et al 2009, Brenner et al 2011, Pearce et al 2012). It is essential that performance and output of CT scanners are tested routinely. "
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    • "There are real public health consequences of these sensational predictions . A recent study observed that when parents of children presenting with isolated head injuries in an emergency department were advised that a CT scan was indicated, but may increase their child's risk of cancer by 1 in 10,000 [based on (Pearce et al. 2012)], willingness to proceed with the scan was reduced by over 20% (Boutis et al. 2013). There is also anecdotal evidence from professionals in the imaging field that articles in the popular press about radiation risks from medical imaging are generating concern among patients (Esz 2013; Fletcher et al. 2013). "
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