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The MUGA scan’s role in monitoring cancer therapy

By DrRich

Dateline: 09/28/2000

Adriamycin (generic name – doxorubicin) is a chemotherapeutic drug that is commonly used, in combination with other drugs, in the treatment of cancer. A serious problem with Adriamycin is that it can be toxic to the heart muscle, and can lead to heart failure.

Doctors have developed strategies to minimize the risk of damaging the heart muscle with Adriamycin. These strategies include: avoiding the drug altogether in patients who already have heart disease; keeping the total dosage given to each patient below a certain “threshold” value; and monitoring the patient’s cardiac function by means of the MUGA scan.

The MUGA scan (MUltiple Gated Acquisition scan) is a noninvasive test that produces a moving image of the heart. From this image, the health of the heart’s major pumping chamber (the left ventricle) can be assessed.

A MUGA scan is performed by attaching a radioactive substance, Technetium 99, to red blood cells, then injecting the red blood cells into the patient’s bloodstream. (The level of radiation to which a patient is exposed during this test is considered minimal.) The patient is then placed under a special camera (a gamma camera), and with some fancy computer manipulation, a “movie” of the beating heart is made. From this moving image, the MUGA scan gives an accurate and reproducible way to measure the ejection fraction of the left ventricle.

The left ventricular ejection fraction (LVEF) is an excellent measure of overall cardiac function. The ejection fraction is simply the proportion of blood that is expelled from the ventricle with each heart beat. So, for instance, if the left ventricle ejects 60% of its blood volume with each beat, the LVEF is 0.6. (A normal LVEF is 0.5 or greater.)

While there are other ways to measure the LVEF (such as the echocardiogram), the MUGA scan measures it more accurately than any other method. In situations where it is important to detect minor changes in a patient’s LVEF – such as in following patients receiving Adriamycin – most experts believe the MUGA scan is the best test available.

Before a patient receives their first dose of Adriamycin, a MUGA scan is usually performed, both to establish a baseline LVEF, and to rule out pre-existing cardiac disease. The MUGA scan is then repeated after a certain amount of Adriamycin is administered (400 milligrams of Adriamycin per square meter of surface area – a number determined by the patient’s height and weight). More MUGA scans are repeated periodically, as more Adriamycin is given. If the patient’s LVEF begins to decrease, then the doctor and patient must reconsider the risks and benefits of continuing with Adriamycin in view of this apparent early cardiac toxicity.

Thus, the MUGA scan plays an important role in allowing Adriamycin to be used in the treatment of cancer, while minimizing the risk of cardiac toxicity.

Here's a link that shows what a MUGA scan looks like.

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