Imaging procedures increase cancer risk

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Low doses of ionizing radiation from cardiac imaging procedures after acute myocardial infarction may increase patients' risk for cancer, study findings published in the Canadian Medical Journal indicate.

“These results call into question whether our current enthusiasm for imaging and therapeutic procedures after acute MI should be tempered,” Mark J. Eisenberg, MD, of McGill University in Montreal and colleagues wrote.

In a cohort of 82,921 patients cancer risk increased by 3% with every 10-millisievert (mSv) of low-dose ionizing radiation. All patients experienced a myocardial infarction between April 1996 and March 2006, and had been included in an administrative claims database.

Although increased risk was observed in both men and women, radiation exposure resulted in a 50% higher hazard among men than women in the mean five-year follow-up period.

No regulatory controls currently exist to guide or limit patient radiation exposure, but study results revealed that average cumulative radiation exposure due to cardiac procedures was 5.3 mSv per patient year.

“We should at least consider putting into place a system of prospectively documenting the imaging tests and procedures that each patient undergoes and estimating his or her cumulative exposure to low-dose ionizing radiation,” the researchers wrote.

In the first year after MI, data indicated that 77% of patients underwent at least one cardiac imaging session or therapeutic procedure that involved low-dose radiation exposure. The most common procedures were percutaneous coronary intervention (40.7%), myocardial perfusion imaging (33.8%) and diagnostic cardiac catheterization without intervention (31.1%).

Mean radiation doses associated with various procedures are as follows: perfusion imaging, 15.6 mSv; PCI, 15.0 mSv; cardiac resting ventriculography, 7.8 mSv; and diagnostic catheterization, 7.0 mSv.

Patients experienced a total of 12,020 new cancer diagnoses during follow up in the abdomen and pelvis (41.9%),  thorax and breast (26.8%) and bone, soft tissue and skin (22%).

“Although these patients most likely will die of cardiac-related causes, the increased exposure to low-dose ionizing radiation increases their risk of cancer and perhaps mortality,” the researchers wrote.

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