Kaiser Health, one of the oldest and largest clinics in the US, in its recent Health News, described a 55-year old woman whose doctor recommended a CT scan of her abdomen, but she didn’t want it. She questioned if the scan was really necessary, because It would be her fourth scan in 8 years, and she was worried about the amount of radiation she was receiving from all the scans.
Her doctor listened, and agreed to treat her diverticulosis without a new scan. The Kaiser article mentions that more and more patients and doctors are becoming concerned about radiation exposure from too many CT scans.
The American Food and Drug Administration notes that the dose of radiation from a single CT is “not much less than the lowest dose of 5 to 20 mSv received my some of the Japanese survivors of the atomic bomb.”
CT scans are fantastic tools to see inside the body, but the problem is that to create these images, the CT scanner takes many individual x-rays from different angles so the CT scan software can reconstruct what are basically 3D images. So the amount of radiation exposure the patient receives is far greater than with a standard x-ray.
For example, a person undergoing a typical CT scan of the abdomen receives the equivalent radiation of 200-chest rays, or 1,500 dental x-rays. And some CT scans give much more radiation. A study at a New York hospital found that some patients who underwent several heart imaging scans had received the equivalent radiation of 5000 chest x-rays during the course of their exam.
Radiation exposure, whether from a nuclear blast or from excessive radiation from too many CT scans, does not increase the risk of cancer instantly, but takes many years to develop. Radiation causes damage to the DNA inside our cells, and the cancers that may take 20 to 30 years to develop. The cancers most likely to develop are leukemia and certain solid tumors such as brain cancer.
Various studies have tried to calculate the risk that an individual CT scan would cause a person to develop cancer. The National Cancer Institute (USA) estimates an additional risk of developing fatal cancer from a single CT scan is 1 out of 2000. Meaning, for every 2000 scans performed, one person will develop a cancer from the radiation received. Note however that the risk is cumulative, meaning that if a person receives multiple scans during their life, the risk is much higher.
All this news is disturbing, but we need to look at the big picture, and realize that most CT scans are medically necessary and provides more help than potential harm. Doctors can see inside the body in almost a miraculous way. In many cases, if there wasn’t a scan, a surgery would be necessary to see what is going on. The important point is to be aware that CT scanning should be done only when medically necessary.
The Food and Drug Administration has estimated that 30 to 50 percent of CT scans performed in the United States are “medically unnecessary”. Many of these 30 to 50 percent were scans being repeated without good reason, or the patient could have had another type of imaging study that does not use the type radiation that causes cancer.
If your doctor wants to do a CT scan
Ultrasound and magnetic resonance scans (MRI) are two types of alternative imaging studies that do NOT increase a person’s chance of developing cancer, since they do not use ionizing radiation. CT scans, and the newer PET scans, however, do use ionizing radiation.
So if a doctor recommends a CT scan, what should a patient do? First, ask the doctor if an alternative type of test such as ultrasound or a resonance scan could be done instead. And if a CT scan was done in the past, ask the doctor if a new scan is really needed. This is especially true if the patient is a child, as younger bodies are more susceptible to the cancer-causing effects of radiation.
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