Dearth of data lowers the bar in debate over radiation and cancer

May 21, 2010

Radiologists have come to expect rising demand for CT, which is why anecdotal reports of sudden and dramatic falls in CT volumes have sent a shudder through the community. All the more alarming is that the rumored drop-offs are coming at the request of patients who want nothing to do with CT because they fear its radiation will someday cause cancer. Instead they reportedly are demanding ultrasound or MRI because neither has ionizing radiation -- never mind that neither is indicated, nor, particularly in the case of ultrasound, has much chance of providing useful information.

Radiologists have come to expect rising demand for CT, which is why anecdotal reports of sudden and dramatic falls in CT volumes have sent a shudder through the community. All the more alarming is that the rumored drop-offs are coming at the request of patients who want nothing to do with CT because they fear its radiation will someday cause cancer. Instead they reportedly are demanding ultrasound or MRI because neither has ionizing radiation-never mind that neither is indicated, nor, particularly in the case of ultrasound, has much chance of providing useful information.

This fear is rooted in the lack of radiation and cancer data that pertain directly to patient exposure to x-rays. The linkage between diagnostic radiation and cancer stems largely from research performed on victims of the atom bombing of Hiroshima, which, after a billion dollars and 60 years, continues to stir debate.

Clinical research studies examining the potential of CT exposure to cause cancer are under way, but it could be years, even a decade, before the results are known. Even then, they may not be conclusive. In the meantime, the tenuous link between radiation and cancer appears to be driving a wedge between patients and the diagnostic technology that can help them.

In response, a tit-for-tat kind of argument countering atom bomb˜based reasoning has surfaced among medical imaging advocates, who suggest that a little radiation-like the amount given during a CT exam-might be a good thing. The underlying theory is called hormesis. Contrary to the widely held belief that effects from low doses of ionizing radiation accumulate until they have the same detrimental effects as high-level radiation, hormesis contends that low doses actually have a beneficial effect that may, in fact, prevent cancer.

Believers in this hormetic effect got a boost from a recent study of cell phone use and its potential for causing brain tumors. The study failed to forge a causative link between cancer and cell phone use. But some data suggest that heavy cell phone users are more predisposed toward some cancers, and that light or moderate users showed less cancer incidence.

Investigators claim the two findings are anomalies. But advocates of hormesis have latched onto the cell phone research as an example of how some radiation exposure can be good. Advocates of CT argue that given the superficiality of the atom bomb data as they relate to medical x-ray, hormesis deserves as much consideration.

If there is a lesson to be taken from the current debate, it is that just as nature abhors a vacuum, scientific debate abhors a lack of evidence, and it will pull in anything that comes close-hormesis and atom bomb findings alike.