Computed tomography-induced cancer risk may be overstated

Dec 24 2012

By Lynda Williams, Senior medwireNews Reporter

Clinicians should be careful not to overemphasize the risk for radiation-induced cancer when counseling patients on undergoing surveillance computed tomography (CT) imaging, caution US scientists.

The team from Massachusetts General Hospital in Boston used a Markov model of testicular cancer to demonstrate that the delayed timing of radiation-induced cancer can mean that the risk to a patient's life is outweighed by the potential benefit of early detection of recurrent disease.

"If a physician compares these risks directly, without taking into consideration the difference in timing, these risks may appear similar," the researchers explain.

"However, if given the choice between equal risks of dying now, versus dying several years from now, most patients would understandably choose the latter; these 'equal' risks are not equal."

In their example of 33-year-old men undergoing CT surveillance in the decade after orchiectomy for stage I seminoma, the lifetime mortality risk from testicular cancer was only slightly higher than the associated risk from radiation-induced malignancy, at 598 versus 505 events per 100,000.

However, the life expectancy loss attributed to testicular cancer was three times that attributed to radiation-induced cancer, at 83 versus 24 days.

The researchers explain that a timing paradox exists which means that that differences in life expectancy loss attributable to testicular cancer versus radiation-induced cancer are more pronounced in younger men than the differences in lifetime mortality risk.

Thus, for 33-year-old men with nonseminomatous germ cell tumor (NSGCT) - which has higher testicular cancer-specific mortality and requires less CT surveillance than seminoma - the lifetime mortality attributable risk to testicular cancer was relatively higher than that of radiation-induced cancer, at 2243 versus 262 cases per 100,000. Life expectancy loss from testicular cancer versus radiation-induced cancer also had a greater difference, at 311 versus 12 days.

When the researchers added in chest CT to NSGCT patients, the lifetime mortality risk attributed to radiation-induced cancer rose to 454 cases per 100,000 and a life loss expectancy of 22 days.

Lead author Pari Pandharipande commented on the findings in a press release: "Radiation-induced cancer risks, often discussed at the population level, can be challenging to conceptualize and apply to imaging decisions that have to be made at the patient level.

"We as physicians can benefit from dedicated educational efforts to improve decision making and better convey the risks to patients."

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