Letter: Risk overplayed?

From Roger Cox, National Radiological Protection Board

Balancing the benefits of medical irradiation with risk of cancer is an issue of growing importance. There are recognised difficulties in developing informed judgements and communicating them to patients, particularly when cancer predisposition is known or suspected. Your recent article on the risks of mammograms for certain women includes quotes from me and others that relate to this issue (9 November, p 10).

The German researchers quoted have coupled selected radiobiological data on abnormal cells in culture with ill-defined calculations of breast cancer risk to support claims of very high cancer risks from mammography in young women who are genetically predisposed. In my view, these calculations are not at all helpful. First, the radiobiological data used are not representative: other investigators do not judge that low-energy mammography X-rays have such high biological effectiveness (British Journal of Radiology, vol 62, p 910, and Radiation Research, vol 158, p 13).

Secondly, the cancer risk estimate made is unpublished and, given the data available, must make a series of unspecified assumptions about how much more sensitive to radiation breast tissue is in a woman with a predisposition. The calculation, as quoted, suggests that a cumulative dose of 40 milligrays, which would typically be received from 10 mammograms, to the breast of a genetically predisposed woman less than 20 years old would more than double her lifetime risk of breast cancer from, say, around 50 per cent to 100 per cent. In my view, this is biologically implausible, somewhat at odds with a recent epidemiological study (Cancer Causes and Controls, vol 13, p 711) and extremely difficult to reconcile with the fact that by the time a woman is 40 years old she will have accumulated a similar dose from natural background radiation.

And is a medical scenario which assumes 10 mammograms before age 20 at all realistic?

Didcot, Oxfordshire, UK