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Canadian study affirms cancer risk from heart imaging
 
 
  February 7, 2011 Reed Miller, www.theheart.org
 
Montreal, QC - Another registry study confirms that low-dose radiation from cardiac imaging raises a patient's risk of cancer [1].
 
Results from a cohort study of over 82 000 patients in the Quebec Med-Echo registry by Dr Mark Eisenberg (McGill University, Montreal, QC) and colleagues are published online February 7, 2011 in CMAJ.
 
The cohort included patients from all over Quebec who were admitted to a hospital with acute MI between April 1996 and March 2006 and had no history of cancer. The registry documented all cardiac imaging and therapeutic procedures involving low-dose ionizing radiation and estimated the patients' exposure based on the average effective radiation dose for that procedure, ranging from 15.6 mSv for myocardial perfusion imaging down to 7 mSv for diagnostic cardiac catheterization.
 
A statistical analysis to adjust for the patients' age, gender, and exposure to low-dose ionizing radiation from noncardiac imaging found that for every 10 mSv of low-dose ionizing radiation a patient was exposed to, his or her risk of developing cancer within five years increased 3%. Of the 82 861 patients included in the cohort, 77% underwent at least one cardiac imaging or therapeutic procedure with low-dose ionizing radiation in the first year after an acute MI. The cumulative exposure to radiation from cardiac procedures was 5.3 mSv per patient-year, of which 84% was in the first year. The patients were diagnosed with a total of 12 020 incident cancers during the follow-up period. As reported by heartwire, cardiologists, radiologists, and patients are increasingly concerned about long-term effects of the low-dose radiation exposure of patients undergoing some kinds of cardiac imaging, especially patients likely to undergo multiple scans, including MI patients. Eisenberg et al's study appears to support the recent findings by Einstein et al that MI patients undergo a median of 15 procedures that expose them to radiation and about a third of these patients receive a total dose greater than 100 mSv [2]. "The potential increase in cancer-related death associated with exposure to radiation from cardiac imaging and therapeutic procedures has to be weighed against the potential risk of death from cardiovascular diseases for which these procedures are indicated and the resulting decrease in mortality expected with their use," Eisenberg et al write. However, this study is not enough to show where the "balance between these competing risks falls" because it is relatively short and could have been influenced by unknown confounding variables. In an accompanying editorial, Mathew Mercuri (McMaster University, Hamilton, ON) and colleagues suggest that "a strategy to track radiation doses may help physicians and patients stay aware of the cumulative exposure" and that healthcare and nuclear industries have systems for monitoring exposure to employees, but there currently isn't any national system for tracking exposure in patients [3].
 
This study was funded in part by a grant from the Canadian Institutes of Health Research.
 
Sources
 
1. Eisenberg, Afilalo J, Lawler P, et al. Cancer risk related to low-dose ionizing radiation from cardiac imaging in patients after acute myocardial infarction. CMAJ 2011. DOI:10.1503/cmaj.100463. Available at: http://www.cmaj.ca.
 
2. Einstein A, Weiner S, Bernheim A, et al. Multiple testing, cumulative radiation dose, and clinical indications in patients undergoing myocardial perfusion imaging. JAMA. 2010; 304:2137-2144.
 
3. Mercuri M, Sheth T, and Natarajan MK. Radiation exposure from medical imaging: A silent harm? CMAJ 2011; DOI:10.1503/cmaj.101885. . Available at: http://www.cmaj.ca
 
 
 
 
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