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Published on April 11, 2016

Low-dose CTs reduce radiation riskct-scan-results

CT or “CAT” scans provide doctors with multidimensional images of amazing clarity by shooting X-rays via a projector that revolves around a patient’s body. The images come at a cost, however, since the amount of radiation used in some U.S. health facilities can be hundreds of times that of a typical chest X-ray.

Concerned with minimizing patient exposure, Cape Cod Healthcare uses only “lower-dose” CT machines augmented by software and staff practices to further limit dosage, said Salvatore G. Viscomi, MD, chairman of the radiology department of Cape Cod Hospital.

Six new units were installed in Cape Cod Healthcare’s facilities on the past two years – two at Falmouth Hospital and four at Cape Cod Hospital.

“We’re using significantly decreased radiation doses than we were 5 to 10 years ago” said Dr. Viscomi. “We’re talking a fraction of what we used to do.”

The amount of radiation used in computed tomography (CT) scans varies with the patient’s body mass, and the organ or area being scanned, he explained. But, for a typical low-dose Chest CT scan used for lung cancer screening, the radiation exposure might be equivalent to five chest X-rays, or a year’s exposure to natural background radiation (not including exposure to sunlight or from air travel). Even that small amount “is not insignificant,” he said.

Radiation Exposure Concerns

The CT machines’ precision allows technicians to better contain radiation to the area being examined.

Radiation exposure remains a concern because it can damage cells and result in cancer or mutations, particularly in the pediatric population. But according to the federal Food and Drug Administration, that risk “is thought to be very small for radiation doses of the magnitude that are associated with CT procedure,” and estimates of the risk “have a broad range of statistical uncertainty.”

The FDA places the risk of eventually developing a fatal cancer from a CT dose of 10 mSv (millisieverts) at 1 in 2,000. The agency compares this with the one in five risk in the U.S. population of dying of cancer.

Dr. Viscomi, who also works as an attending physician at Brigham & Women’s Hospital in Boston and as an instructor at Harvard Medical School, said his professional contacts make him aware of new developments in radiology, sometimes even before a scientific paper detailing an advance is published.

“We’re continuing to look at our protocols to continue to reduce radiation,” he said. “I’m really aggressive in pushing the envelope as low as they can go.”

How Much Exposure Do You Get?

According to the American College of Radiology and the Radiological Society of North America, CT scans range from 1.5 to 20 mSv, depending upon the procedure. These organizations estimate a 3 mSv CT scan exposure as equivalent to a year’s worth of natural radiation.

The CT machines Cape Cod hospitals use software programs to limit exposure while improving images, as just reducing radiation alone can result in grainy images, said Dr. Viscomi. The program removes “noise” from the data and creates a clear image. Another program lessens the amount of radiation directed toward the front of a patient’s body.

“Several organs in the front of the body are more radiation-sensitive,” such as the lens of the eyes, breasts, and thyroid gland, he said.

To avoid excessive CT scans, Cape Cod Healthcare radiologists check patients’ histories to see how many scans they’ve undergone. They also evaluate whether another form of imaging, such as ultrasound or an MRI, might be more appropriate.

“A lot of our patients have chronic diseases and may have more than one CT scan,” he said.

“In general, CT scans are used to efficiently search for the cause of a problem in the emergent setting but also to follow up changes in a patient’s chronic condition.”

An MRI (magnetic resonance imaging, which uses radio waves and a powerful magnetic field to form images) may be better for examining specific locations, but can take 45 minutes to perform, he added. In an emergency situation, physicians may prefer the speed of a CT scan that can be done in seconds.

One of the CT procedures offered at Cape Cod Hospital is screening of smokers older than 55 for lung cancer. The dosage is about one-fourth of the typical low-dose scan and similar to the radiation exposure of a screening mammogram, he said.

“The benefits highly outweigh the risks,” Dr. Viscomi said. “Tumors are more likely to be found smaller, at earlier stages and before they spread to other parts of the body. Mortality from lung cancer decreases by 20% with CT lung cancer screening.”

Dr. Viscomi credited Cape Cod Healthcare’s CEO and president, Michael Lauf, with supporting the purchase of the low-dose machines and efforts to keep the radiology department equipped with the newest procedures and technology.

“We’re certainly on the cutting edge and will continue to adapt our practice to continue to be so,” he said.