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CT radiation doses
  1. K McHugh
  1. Radiology Department, Great Ormond Street Hospital for Children, London WC1N 3JH, UK; kmchugh{at}gosh.nhs.uk

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The hazards of computed tomography (CT), in terms of radiation, are being increasingly recognised. CT scanning, despite representing less than 5% of the total number of x ray procedures performed, contributes approximately 40% of the total collective radiation dose to the UK population from all medical x ray examinations.1 It is well known that children are more radiosensitive than adults—for example, a 1 year old infant is 10–15 times more likely than a 50 year old adult to develop a malignancy from the same dose of radiation.2 In addition, for a given procedure, the effective (radiation) dose is larger in a small infant than in an adult—that is, the effective dose increases as age decreases.2 It has been alleged that, “the lifetime mortality risk attributable to the radiation exposure from a single abdominal CT in a 1 year old child is in the order of one in a thousand”.2 CT scanning, therefore, is a potentially dangerous modality, and when used in children in particular, the dose should be kept as low as reasonably achievable (the so-called ALARA principle).

A recent Images in Paediatrics case contained one important piece of CT information in an otherwise excellent CT image of a lipoblastoma (admittedly far more immediately dangerous than a CT study).3 The CT examination of the lower chest was done in a 6 month old baby using 250mA (mA = milliamperage, which is the main determinant of CT dose). Unless the authors have an extremely old scanner, this is an adult setting and is much too high for a child. A perfectly good diagnostic study can be done in an infant of this age with an mA of 50, which is one fifth of the dose. In fact, an adequate study might even be achievable with an even lower mA, but the CT scanner manufacturers have been slow to facilitate such low dose techniques, ignoring the needs of children. Using excessive adult CT doses in children is, in my experience, an unfortunately common error in the UK. This has also been noted in the USA.4 The message is slowing filtering through to the radiology community, but paediatricians should be aware as well. CT is a high dose radiation technique—if a CT study is truly justified in a child then weight (not age) adapted paediatric parameters should be used, which can give adequate diagnostic information with minimised radiation risk.

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