In this issue, we look at CT scans.
The ECI recommends the ACEM-RANZCR Guidelines on Diagnostic Imaging for EDs as a great practical tool to assist us all with clinical decision making concerning choice of imaging study.
There have been a number of articles this year about the use and risks of CT scans. The following provides a summary of recent literature...
In June a team based at the Royal Victoria Infirmary at Newcastle upon Tyne, England, published results in the Lancet (1) of a large-scale observational retrospective cohort study of patients examined by computed tomography (CT). The paper entitled “Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours” found that in children aged younger than 15 years “cumulative ionising radiation doses from 2-3 head CTs could almost triple the risk of brain tumours and 5-10 head CTs could triple the risk of leukaemia”. They interpret this as being “one excess case of leukaemia and one excess case of brain tumour per 10,000 head CT scans” (for patients younger than 10 years in the 10 years after the first scan). The authors’ concluded that “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”.
Commenting in the Lancet Einstein (2) considers this an important paper. Previously risks of cancer from CT scans were always in a sense theoretical e.g. based on studies of survivors of the atomic bombs in Japan. He noted that “many medical practitioners suggested that the evidence for cancer risk associated with CT scanning was speculation”. Einstein considers the new study should “reduce the debates about whether the risks from CT are real”. The publication of the study by the team at the Royal Victoria Infirmary initiated a number of other letters to the Lancet (3). These point out potential methodological issues with the study. In particular, it is difficult to exclude other hidden factors as being an influence in the study, which might undermine the findings.
Also published this year, a report in the British Journal of Radiology (4) sets out concerns about the potential for inappropriate usage of diagnostic medical exposures involving radiation. They reported “a significant level of inappropriate usage, and, in some cases, a poor level of awareness of dose and risk among some key groups involved” and that “authoritative sources suggest that a significant fraction (20-50% in some areas) of radiological examinations may be inappropriate”. They also found that the “extent of use of radiology has become a matter of concern for many reasons, including population dose, individual dose, budgetary and financial issues, and finally the appropriateness of the examinations or justification”. They concluded that “Clinical Audit was regarded as a key tool in ensuring that
justification becomes an effective, transparent and accountable part of the normal radiological practice. In summary, justification would be facilitated by the “3 As”: awareness, appropriateness and audit”.
Another study in the Archives of Pediatrics & Adolescent Medicine (5) suggests that parental anxiety is a driver for potentially inappropriate CT scans. The US study looked at children with non-trivial minor blunt head trauma in 2004-6. It found that “children of black non-hispanic or Hispanic race/ethnicity had lower odds of undergoing cranial CT among those who were at intermediate risk (odds ratio 0.86) or lowest risk (odds ratio 0.72) for clinically important traumatic brain injury”. The conclusion being that “medically irrelevant factors, such as patient race/ethnicity, can affect physician decision making, resulting in exposure of children to unnecessary health care risks”. They report that “parental anxiety and request was commonly cited by physicians as an important influence for ordering cranial CT
in children of white non-hispanic race ethnicity”.
In conclusion, the health risks from CT scans and up till now were based on somewhat theoretical studies. However, a recent study provides a quantification of the risk based on a large cohort study of patients. This raises a number of resulting policy and practice issues, including consent, use of variable CT dosing, justification and auditing. Added to this, the responsibility of all physicians to provide appropriate care, and appropriate resource stewardship.
References:
1. Pearce 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, 4–10 August 2012; 380: 499–505. (also published online 7 June 2012).
2. Einstein AJ. Beyond the bombs: cancer risks of low-dose medical radiation. Lancet, 4-10 August 2012; 380: 455-457 (also published online 7 June 2012).
3. Correspondence to Lancet (various). Lancet, 17 November 2012; 380: 1735-1737.
4. Malone J, Guleria R, Craven C. Justification of diagnostic medical exposures: some practical issues. Report of an International Atomic Energy Agency Consultation. The British Journal of Radiology, May 2012; 85: 523-538.
5. Natale JE, Joseph JG, Rogers AJ. Cranial Computed Tomography Use Among Children With Minor Blunt Head Trauma. Archives of Pediatrics & Adolescent Medicine, Vol 166 (no.8), Aug 2012; 732-737.
