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More on CAT Scans and Cancer

Friday, October 29, 2010 // Uncategorized

8/18/2009 10:13:21 PM

Coronary calcium scoring has been advocated by some as a screening test for patients at risk for coronary artery disease.

Prognostic Value of Absence of Coronary Calcium

The absence of coronary calcium was associated with low event rates, especially in asymptomatic patients.

Elevated coronary calcium scores are associated with greater burden of atherosclerotic disease. To determine whether the absence of calcium as identified by computed tomography identifies a population at low risk for adverse cardiac events, U.S. investigators conducted a meta-analysis of 49 articles in which the diagnostic and prognostic values of coronary artery calcification were addressed.

In 13 studies that involved 65,000 asymptomatic patients, 25,903 did not have coronary artery calcification; only 146 of such patients (0.6%) experienced adverse cardiac events during a mean follow-up of 51 months. In seven studies in symptomatic cohorts, 17 of 921 patients (1.8%) without coronary artery calcification had adverse cardiac events during a mean follow-up of 42 months.

Comment: In this large meta-analysis, the absence of coronary calcium was associated with low event rates, especially among asymptomatic patients. Unsurprisingly, event rates in symptomatic patients were somewhat higher. However, editorialists remind us that more data are needed to determine when scans such as these add incremental prognostic value to standard assessments and whether calcium scoring will lead to improved treatment and outcomes.

Kirsten E. Fleischmann, MD, MPH

Published in Journal Watch General Medicine July 28, 2009

It’s not clear from this what the risk factors for the populations studied were.  It doesn’t make sense to do on everyone, but it may make sense to do on patients with multiple risk factors in whom aggressive lipid/blood pressure lowering is being considered.

The test is not completely without risk as can be seen from the following article.

Cancer Risk from Coronary Artery Calcium Screening

Researchers estimate that radiation exposure from coronary CT could lead to excess lifetime cancer risk.

Recently, multidetector computed tomography scanners have become the modality of choice for assessing coronary artery calcium (CAC). In this study, researchers estimated risk for developing cancer from CAC screening with CT scanners. Because no standardized CAC screening protocol exists, researchers reviewed protocols that were used in cardiac studies. Cancer risk was estimated primarily from data on Japanese atomic bomb survivors.

The effective radiation dose delivered from a single CAC screening study ranged from 0.8 to 10.5 millisieverts (mSv) across the different scanning protocols. For the median dose of 2.3 mSv, a single screening at age 55 would result in a lifetime excess cancer risk of 8 cases per 100,000 men (lung cancer would account for 6 cases) and 20 excess cancer cases per 100,000 women (lung cancer would account for 14 cases and breast cancer for 4 cases).

Comment: Current technology allows CAC screening at a substantially lower dose (approximately 1 mSv) than the dose used in this analysis (2.3 mSv). In contrast, a mammogram delivers approximately 0.5 mSv of radiation, and an abdomen and pelvis CT scan delivers approximately 10 mSv. The American Heart Association considers CAC screening to be reasonable in intermediate-risk patients (class IIB recommendation) but not in low- or high-risk patients. The U.S. Preventive Services Task Force recommends against routine screening for CAC. Imaging sites should use protocols that deliver the lowest possible radiation dose; otherwise, CAC screening should not be performed.

Jamaluddin Moloo, MD, MPH

Published in Journal Watch General Medicine August 18, 2009

As pointed out, these screens can be done at a radiation dose that is approximately twice that of a screening mammogram.  A CTA or CAT scan angiogram involves contrast or dye and involves a substantially higher radiation dose.  It delineates the arteries and is more sensitive at detecting plaques than a calcium score which just detects calcium deposits in longstanding plaques.  The other potential risk is the detection of “incidentalomas”.  These are unexpected findings which are probably innocous, but require further testing to insure that they are.  This involves risk from additional radiation or complications of a biopsy.

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