Friday, October 06, 2006
Carcinogenic Diagnosis
From the current issue of the Hastings Center Report
BY ADRIAN FUGH-BERMAN

If a diagnostic procedure increases cancer risk, should patients be informed of that risk? Apparently not, at least for one procedure performed more than 150,000 times a day in the United States.¹ CT scans use multiple x-rays to create three-dimensional images that are diagnostically useful but expose people to far more radiation than conventional x-rays. In fact, one CT scan exposes a patient to the lower range of radiation received by some Nagasaki bombing survivors. Up to one in a thousand patients will develop cancer from this exposure.² Sixty million CT scans a year will thus cause cancer in thousands of people. Yet most consent forms are silent about this.

The cancer-causing effects of CT scans are routinely discussed in the medical literature, and some researchers have worried about the long-term effects, especially in children, who have more dividing cells to disrupt and more time to develop cancer. Others trivialize the risk, arguing that the benefits are worth it. Yet patients undergoing CT scans are informed of the much rarer risks of serious complications and deaths (one in 400,000) caused by injection of iodinated contrast material. Serious allergic reactions are dramatic and almost immediate, but most people will survive even severe allergic reactions, especially when they take place in a health care facility. Cancers may take decades to manifest, but can be devastating. And that an effect is delayed is hardly justification for not mentioning it; informed consent for cancer treatment includes discussion of the long-term risks of inducing new cancers.

Some researchers have also suggested that since the background risk of getting a fatal cancer is one in five, what’s the harm in a little topping off? Iatrogenic risks are different from the background risks of daily living, however. Besides, the concern is not just that the incidence of cancer will be increased, but that it will occur earlier. One of five people eventually may die of cancer but dying of cancer at age fifty instead of ninety surely makes a difference.

The literature notwithstanding, the silence on medical radiation risks is not due to a conspiracy of doctors: they are largely unaware of the problem. One survey found that less than half of radiologists, and less than a tenth of emergency room doctors, realized that CT scans increased the lifetime risk of cancer.³ Few of either group could accurately compare radiation doses between CT scans and x-rays. Also, physicians may not realize that balancing risks against benefits works better when weighing diseases against treatment than when assessing diagnostics. A cancer treatment may cause heart damage, but the chance of cure may be worth the risk. There are many more variables when assessing diagnostics, including the availability and equivalency of other diagnostic techniques, the fact that all tests are fallible, and the realization that imaging is only part of making a  diagnosis, which is only the first step towards considering treatments.

Surely these risks should be mentioned to patients. Often they can also just be avoided or reduced. CT scans are sometimes superior to other imaging techniques, but in other cases, CT scans can be replaced with magnetic resonance imaging or ultrasound, which do not expose patients to damaging ionizing radiation. Sometimes just a good medical history suffices. One reason for the proliferation of CT scans is the proliferation of CT scanners; once purchased, they bring in more money the more often they are used. Necessary CT scans can be made safer by reducing the dose of radiation and by protecting non-target areas of the body. Protective garments and shields that reduce radiation exposure of the most sensitive tissues (breasts, eyes, and thyroid glands) are commercially available but little used.

1. D.R. Martin and R.C. Semelka, “Health Effects of Ionising Radiation from Diagnostic CT,” Lancet 367 (2006): 1712-14.

2. National Academy of Sciences, BEIR VII: Health Risks from Exposure to Low Levels of Ionizing Radiation (Washington, D.C.: National Academies Press, 2006); Food and Drug Administration, “What Are the Radiation Risks from CT?”.

3. C.I. Lee et al., “Diagnostic CT Scans: Assessment of Patient, Physician, and Radiologist Awareness of Radiation Dose and Possible Risks,” Radiology 231 (2004): 393-98.

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