ACC: Radiation dose in CV imaging--How much is too much?

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ATLANTA--Currently, cardiovascular imaging accounts for 30 percent of all the medical radiation that people receive in the U.S., noted Andrew Einstein, MD, cardiologist and assistant professor of clinical medicine at Columbia University College of Physicians and Surgeons in New York City, during a symposium at the 59th annual American College of Cardiology (ACC) annual conference on Monday. Einstein also spoke to whether the current levels of radiation are appropriate, as well as strategies for reducing radiation exposure.

Einstein described current radiation dose in cardiovascular imaging as “a problem for patients, a problem for populations and a problem for the profession.”

Radiation dose has both deterministic and stochastic effects, said Einstein. The deterministic effects are due to radiation-induced cell death, which only occurs above a specific, typically high-threshold dose and after cells and tissue have been killed by radiation, he noted, explaining that this can vary by individual.

Stochastic effects are due to radiation-induced mutations and the severity does not depend on dose, Einstein explained. The effects can include a neoplasm, which occurs after a latency period. For example, leukemia occurs after a two-year lag period and most solid tumors appear following a lag period of ten years, he said.

In quantifying ionizing radiation, Einstein explained that there are two fundamental approaches that can be employed -- measuring dose and estimating risk. While measuring radiation exposure due to medical imaging is important, it can also be problematic and difficult, he noted.

The sample size necessary to have sufficient statistical power to detect an increase in cancer mortality would need to be very large, and it must include lifetime follow up, explained Einstein. “Really, it’s an issue of statistical power,” he said.

Referring to studies conducted in the past, Einstein referenced the Japanese atomic bomb study in which 120,000 survivors where followed, and an Oxford University study, consisting of 15,000 children, which assessed childhood cancer and its connection to in-utero imaging. Einstein noted that the doses of radiation found by these studies were similar to the doses that cardiovascular patients receive currently.

“At the doses that our patients receive, there is the potential for increased  risk for cancer and that’s why we are concerned,” he said. “That’s why we think there might be a problem.”

This year there are six studies involving between 6,000 and 7,000 patients currently underway collecting data from CT and nuclear medicine scans, said Einstein. Perhaps most noteworthy, a pooled analysis is planned by the United Nations for this year. “We are looking forward to the results [from] this epidemiologic study for our patients, populations and our profession,” he said.

As reports are emerging, along with patient photographs displaying the results of radiation overexposure, Einstein noted that better appropriate use criteria, monitoring of imaging and improved effective dose estimations are necessary. “We shouldn’t be seeing these gory pictures in 2010, but we are,” he explained.

“The FDA is keeping a closer eye on the topic as emerging reports are finding that imaging protocols are not correct and many people are receiving much too high a radiation dose. This gives our profession a bad name,” concluded Einstein.  “The more we police ourselves and practice good medicine, the less regulatory encumbrance we will undergo.”