Debate: How serious is the radiation risk from CT imaging?

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Source: Copper Queen Community Hospital  

In a point-counterpoint discussion this week, Andrew Einstein, MD, of the Mount Sinai School of Medicine in New York City, cautioned cardiologists against the overuse of CT imaging because of studies linking it to cancer risks, while Stephen Balter, PhD, of the Lenox Hill Hospital in New York City, argued that the findings are not as definite. The debate was presented in a series, “Controversies in Cardiac Noninvasive Imaging,” this week at the Transcatheter Cardiovascular Therapeutics conference in Washington, D.C.

Einstein conceded that the data on CT coronary angiography (CCTA) is scarce. However, he said that a comprehensive review of patients who underwent the procedure can be used to predict the lifetime attributable risk (LAR) of cancer incidents related to CTCA.
Einstein examined a study involving Monte Carlo simulations with a 64-slice scanner at 120 kVp and a pitch of 0.2. The analysis was repeated to assess for age, gender and scan type. With a single CCTA scan, a 20-year-old woman had a 1 in 143 chance of developing cancer, but the risk dropped to 1 in 284 by age 40.

The risk was reduced for men and women as they aged, and the overall chances for a man to develop cancer as a result of the procedure are less than that of a woman. Among male patients who received a single CCTA scan at age 20, 1 in 686 men will develop cancer.

At age 40, the risk rises to 1 in 1,000 men, and age 80, it becomes 1 in 3,000 men. Also, Einstein said that a 20-year-old male has almost five times the risk of an 80-year-old male. Therefore, a 20-year-old female has approximately 10 times the cancer risk from a single CTCA scan than a 40-year-old male, he said.

Einstein noted the difference in radiation sensitivity between men and women. For instance, a dose of 100 mSv has more effect in females, according to Einstein. At the age of 20, there were 3,460 female cases of cancer versus 1,490 male cases; and, at age 80, there were 700 female cases versus 340 male cases.

As a result of the statistics, Einstein said that the estimated LAR of cancer incidence in an average 51-year-old woman is 1 in 366.

Einstein also said that patient age needs to be considered. In particular, he warned against recommending CCTA in younger women, and he cautioned against the overuse of CT scans. In fact, Einstein stated that “CCTA should not be done on asymptomatic patients.”

From the opposing perspective, Balter argued that the link between radiation dose and cancer risk are much less defined. He pointed out that the amount of noise is varied by changing the dose distribution, and dose should be managed for the clinical purpose of the scan. He did concede that while “breasts get the same dosage as any other tissue, women are at higher risk.”

Balter agreed that young women are most sensitive to radiation. However, Balter said that a 20-year-old female, who receives a CT scan has a 1.65 percent chance of contracting cancer, and the same age group has a 1.42 percent chance of contracting cancer without a CT scan. A 60-year-old man who has received a CT scan has a 0.49 percent chance of being diagnosed with cancer and without a CT scan, he has a 9.41 percent chance. As a result, Balter said there is no statistical significance to indicate that CT scans directly relate to cancer risks.

In his conclusion, he stated that there is little clinical data to support that CT with doses below 100 mSv are clearly linked to cancer risks.