Alarm about computed tomography scans is unjustified

To the Editor: We agree with Mendelson and colleagues1 about the need to ensure radiation doses of computed tomography (CT) are as low as reasonably achievable while maintaining diagnostic quality of the images. Perceived benefit to the patient must be balanced against theoretical small risks from the procedure. The uncertainty surrounding risk estimates at the lower end of the radiation dose range means that it is important for radiologists to take responsibility for monitoring radiation dosimetry. This becomes especially important when imaging young people with chronic disease (such as renal calculi, chronic hepatitis, cystic fibrosis and inflammatory bowel disease), who may have many CT scans while young. As stated by Mendelson et al,1 the theoretical risks are assumed to be cumulative over a lifetime, but diminish significantly the older the person is at time of exposure.

We would like to highlight work that the Royal Australian and New Zealand College of Radiologists (RANZCR) has undertaken to support the development of CT scanning standards, professional education, dose optimisation and the establishment of national diagnostic reference levels by the Australian Radiation Protection and Nuclear Safety Agency.

CT dose optimisation quality improvement programs have been conducted in Queensland and Victoria. These have been funded through a grant to the RANZCR Quality Use of Diagnostic Imaging (QUDI) Program from the Australian Government Department of Health and Ageing. A dose optimisation project is planned for South Australia in 2011. The RANZCR QUDI program has developed a consumer and referrer information database of diagnostic imaging procedures, including a general item about the theoretical risks associated with ionising radiation. This information is accessible at http://www.insideradiology.com.au and supports informed choices about imaging.

While Blecher2 and Mendelson et al1 are correct in indicating that the latest multidetector computed tomography (MDCT) platforms have the potential to deliver acceptably low radiation doses and high-quality images, this is not always seen in practice, based on the evidence from these optimisation programs. Some multiphase MDCT protocols have the potential to give rise to organ doses in the range where there is little doubt that a small increased risk of carcinogenesis exists.3,4

Contrary to the comment made by Blecher,2 our knowledge of the impact of radiation on humans does not arise exclusively from atomic bomb survivors. For example, we have evidence of increased breast cancer risk from patients who underwent multiple fluoroscopic examinations to monitor treatment for tuberculosis.5 Risk estimates from this and other datasets are broadly consistent with those from atomic bomb survivor data.

In view of the above, we need to be vigilant in ensuring that CT examinations are clinically justified and, secondly, performed using optimised scanning protocols. Referring practitioners need to know that the potential stochastic effects resulting from CT examinations are cumulative over a lifetime. It is this cumulative effect that is not necessarily trivial.