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Primary Care Corner with Geoffrey Modest MD: Cardiac Imaging and Radiation Exposure

6 Nov, 14 | by EBM

The American Heart Association came out with a scientific statement to limit patient exposure to radiation (see here). It turns out (not surprisingly) that despite improved, lower-exposure technology, there has been a 6-fold increase in medical imaging radiation exposure from 1980 to the present, and that 40% comes from cardiovascular imaging and interventions. There is clearly a knowledge deficit: a 2004 study found that <50% of radiologists and 9% of ER docs were aware that CT scans could increase lifetime risk of cancer!!! Extrapolating from current data, women and younger individuals will have higher likelihood of cancer by a procedure, as depicted below (SPECT MPI = single-photon emission CT myocardial perfusion imaging, TC = technetium-99m; CTA = CT angiography).

graph1So, recommendations:

–All clinicians should know which cardiac imaging uses ionizing radiation and what are the typical radiation exposures (there are lots of publicly available sources: see their table 2)

–Those doing the procedures should use the best dose-optimization and minimization techniques (i.e. best images at lowest radiation exposure)

–Patients should be provided with key facts about the procedure, including radiation exposure, along with risks and benefits of alternative procedures when available

So, one example they give is of a patient scheduled for cardiac imaging for CAD evaluation, with the following decision tree:

–Is the study appropriate?

–If so, is imaging without radiation available and comparable?

–If yes, consider that imaging, especially in younger patients. Otherwise, can patient exercise?

— If not, consider CT angiography or PET, if available. If so, then consider SPECT (especially using lowest dose, >1 head, and high-sensitivity camera). If stress-only imaging, then use Tc99m (not thallium-201 which has greater radiation exposure and poorer spatial resolution).

The goal of this AHA statement is to minimize radiation exposure, especially in younger people and women who seem to have higher likelihood of developing cancer over time. Clearly, the benefits of an optimal study with ionizing radiation may well be important (though we should really make sure that the test is necessary and will potentially supply information which could change management) and we know that many-too-many studies are done. See Choosing Wisely, which notes that low-risk patients comprise 45% of unnecessary “screening”, where screening should be limited to diabetics >40 yo, people with peripheral artery disease, or those with >2% yearly risk of CAD event. We should preferentially choose tests which minimize radiation. It is incumbent on the cardiologists/radiologists to make sure their equipment is up-to-date, and provide the lowest radiation exposure possible, though it is not a bad idea for us to ask them/check around for the best alternatives.

Geoff

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