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

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Andrew Einstein, MD, of the Mount Sinai School of Medicine in New York City, and Stephen Balter, PhD, of the Lenox Hill Hospital in New York City, engaged in a debate on the radiation risks involved with CT imaging and in turn, whether the patients should be concerned about cancer. The debate was presented in a series “Controversies in Cardiac Noninvasive Imaging” this week at the Transcatheter Cardiovascular Therapeutics conference in Washington, D.C.

While Einstein conceded that the data on CT coronary angiography (CTCA) is scarce, with a comprehensive review of patients who underwent the procedure it is possible to determine 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. With this device, the scan range of the heart is 15cm and 25cm for the heart and aorta. Effective doses of eight protocols were administered in 21 doses for female patients and 15 doses for males. The analysis was repeated to assess for age, gender and scan type. With a single CTCA scan, a 20-year-old woman had a 1 in 143 chance of developing cancer, and 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 CTCA 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 said that radiation sensitivity is different in men and women. For instance, 100 mSv dosages have a much higher 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 CTCA in younger women, and he cautioned against the overuse of CT scans. In fact, Einstein stated that “CTCA should not be done on asymptomatic patients.”

From the opposing perspective, Balter argued that the link between radiation doses and cancer risks are much less defined. Balter said that you can vary the amount of noise by varying 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 focused on the linear non-threshold model, which states that the higher the dose, the higher the effect.

Among U.S. death statistics in 2003, Balter said that the risk factors were 1 in 24 cases of stroke, 1 in 5 cases of heart disease, and 1 in 7 cases of cancer. In order to determine the cancer risk, the stochastic risk is calculated and multiplied by the effective dose.

According to this standard, 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. He said that a 60-year-old man who have receives 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.

Also, Balter said that one of the reasons people are questioning cancer risks related to CT scans is that the mean age for a CT scan “is about a decade younger than cath lab” treatments.

He stated that there is little clinical data to support that CT with doses below 100 mSv are clearly linked to cancer risks.