The use of CT scanning in the assessment of minor head injury has increased substantially in recent years. Concerns have been raised that this will increase the risk of radiated induced cancer. A study published in the Lancet of 178,604 children and young adults who received a CT scan shows that 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.
Should this influence our decision to use CT in children with minor head injury? Our analysis undertaken suggests that it should, but that clinical decision rules probably provide an appropriate balancing of risks and benefits. We modelled the benefits of CT scanning in minor head injury, in terms of detected and treating serious bleeding, and the risks, in terms of lifetime cancer risk using similar estimates to the Lancet study. The results showed that the best outcomes (measured as quality-adjusted life years) were achieved using CT selectively based on a decision rule. Indiscriminate use of CT scanning worsened outcomes by increasing the cancer risk, while failure to use CT worsened outcomes relating to head injury.
Determining the appropriate balance between sensitivity and specificity for a decision rule is tricky and could do with more detailed study, but our analysis in adults suggested that currently available rules with 98-99% sensitivity and 40-50% specificity have probably got the balance right. It isn’t worth sacrificing specificity below 40% to achieve 100% sensitivity and it isn’t worth sacrificing sensitivity below 95% to improve specificity. It would obviously be great if we could improve both sensitivity and specificity, but diagnostic decision-making usually involves a trade-off between them.
Pearce et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet, published online 7/6/12
Pandor et al. Diagnostic management strategies for adults and children with minor head injury: a systematic review and an economic evaluation.
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