CT scans in childhood and risk of leukaemia and brain tumours

Abstract

Mark Pearce and colleagues1Pearce MS Salotti JA Little MP Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study.Lancet. 2012; 380: 499-505Summary Full Text Full Text PDF PubMed Scopus (2457) Google Scholar claim that the radiation doses from CT examinations in childhood are significantly associated with leukaemia and brain tumours. We would like to highlight some limitations of this study. First, Pearce and colleagues neglect organ dose calculation error. Several published studies2Castellano E CT dose calculations for individual patients—what you should know.http://www.ctug.org.uk/meet10-10-14/CT%20Dose%20calculations%20for%20individual%20patients%20-%20what%20you%20should%20know.pdfGoogle Scholar, 3Jansen JTM Shrimpton PC Calculation of normalised organ and effective doses to adult reference computational phantoms from contemporary computed tomography scanners.Prog Nuclear Sci Technol. 2011; 2: 165-171Google Scholar show that the accuracy of CT dose estimation for individual patients, based on phantom or Monte Carlo simulation, is highly variable, ranging from 25% to 45%. This uncertainty could affect the excess relative risk calculated by Pearce and colleagues. Second, the effective doses associated with CT examinations are not mentioned in the paper, despite the International Commission on Radiological Protection focusing its estimations of radioinduced cancer risk on the effective dose. Use of dosimetric quantities also facilitates comparisons between acquisition protocols and clinical situations. Finally, the doses to the brains of male patients aged 0–5 years seem the same in Pearce and colleagues' study. However, computer models of the dose distributions of ionising radiation in the human body indicate that morphological differences exist between 1 and 5 years.4Lee C Lodwick D Hurtado J Pafundi D Williams JL Bolch WE The UF family of reference hybrid phantoms for computational radiation dosimetry.Phys Med Biol. 2010; 55: 339-363Crossref PubMed Scopus (238) Google Scholar Therefore brain doses in these ages should be different. To design retrospective studies with 23 years of follow-up in the imaging specialty is a true challenge because improvements in technology and especially in dose reduction will have been tremendous over that period. Nevertheless, we agree with Pearce and colleagues that MRI devices, the diagnostic performances of which now compete with those of CT in many diseases, should be encouraged. We declare that we have no conflicts of interest. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort studyUse 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. Full-Text PDF Open AccessCT scans in childhood and risk of leukaemia and brain tumours – Authors' replyWe agree with Jun Deng and colleagues that the risk of leukaemia varies with age at exposure to radiation. Although there was no clear evidence of this in our study, we noted that it might just reflect insufficient statistical power to examine subgroup effects. Our dosimetric phantoms were developed to take account of changes in red bone marrow during childhood.1 Even if there is large variation in the rate of these changes between children, the associated reduction in the accuracy of our dosimetry is unlikely to account for the lack of a relation between leukaemia risk and age at exposure. Full-Text PDF