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The topic of radiation risk from medical imaging has been in the news lately with growing concern over potential dangers, along with programs to minimize exposure. A new web site www.xrayrisk.com allows you to calculate your patients' (or your own) lifetime increased risk of cancer based on the CT scans or X-rays performed.

DOTmed News spoke with the host of the web site, Michael Hanley, M.D., a second-year radiology resident at the Medical University of South Carolina.

DOTmed (DM): We have had a lot of stories on our web site about the dangers of radiation from medical exams and efforts by the American College of Radiology (ACR) designed to limit the problem, including the Image Gently program.

Michael Hanley (MH): Every time I open the paper I see an article on radiation risk. Many news reports make inflammatory claims that are scary for patients. What we tried to do was get real numbers out there with facts about radiation and cancer and how much radiation is involved with different types of medical imaging studies.

DM: So I could go to the site and put in all the mammograms I have had over the years?

MH: The site features a calculator where you can pick a study, enter your age and gender then calculate the additional risk of cancer based on the radiation exposure from those medical tests.

Screening mammograms are unique in that they are performed on health patients, making the weighing of risks and benefits much more important. The reason mammograms are recommended is because they have been proven to save lives. One of the worst things that could come of all the news media attention is that people wouldn't go to get a test like that, which would be bad for women and bad for everybody.

Alternatively, if a patient presents to the emergency room with a cough and fever, it is absolutely indicated to have a chest X-ray. You should never even think of the risk [of radiation exposure] because the risk of something bad happening because of an untreated pneumonia is so much greater than the tiny assumed risk of cancer ten years down the line.

DM: How dangerous are medical tests exactly?

MH: If you had 100 chest X-rays, you couldn't even get whole numbers [such as a one percent increase] in your lifetime risk of cancer. If you enter 100 chest X-rays into the website's calculator, you'll find that increases your risk of cancer 0.09 percent. This is added to a background risk of 45% for men. So, in general, people should not be scared of chest X-rays and mammograms.

The concern arises with CT scans because CT scans are hundreds of times more radiation than a chest X-ray. A chest CT is about 500 times the radiation of a chest X-ray. So that's a big difference. If a doctor orders a chest CT, patient should feel comfortable asking why. If there is good reason, again there is little reason to worry about the cancer risk.

If you select a chest CT on the website, the risk is still very small, but by using the calculator at least we can open up a conversation and have real numbers when people talk about this.

DM: Isn't the real issue here about children?

MH: Yes. In the "About" section of the (www.xrayrisk.com) website, (the middle graph), the risk for children is shown on the left and adult on the right from the same radiation dose. This demonstrates increased risk for the young partly because the cancers that are induced by radiation take 5-10 years to develop. So if you are 80 years old, get all the CT scans you want.

Most physicians are very cautious with children and the doses on the site are adult doses. There has been a strong campaign by the ACR to make sure people aren't using adult doses for kids (Image Gently). They have done a great job of bringing down the dose.

DM: What about radiation risk for the health care professionals such as the technologist? Are they under any increased risk?

MH: Yes, and the National Committee on Radiological Protection and Measurements (NRCP) monitors their risk. Hospitals have physicists whose job is to ensure their safety. I wear a badge that I replace very month. I send it in to a company and they tell me what my radiation dose was for the month. The government sets yearly limits, so if I were to go above the safe limit, then I would not be able to do some procedures.

DM: So interventional radiologists are at greater risk.

MH: Yes, those physicians get some of the highest radiation doses from working. Most of my days are spent behind a computer reading X-rays or CT scans
and I get no radiation exposure.

For an interventional radiologist who reads X-rays live to do procedures, they do get larger doses and are monitored very closely by the government and the hospital administration to make sure that this is done safely. The exposure limit for workers is 50 mSv per year, which is equal to about 7 chest CTs. The technicians who take the X-rays have equipment that lets them stand far away or behind a wall. But they are also monitored and protected. Exposure falls off every quickly just a few feet away from the equipment.

DM: How much radiation exposure do health care professionals receive?

MH: Other than interventional radiologists, the people who get the most are the technicians. They get about 2 mSv per year, in general that is about the same as getting a head CT.

It is important to point out that there has never been a reported case of cancer as the result of medical imaging. Most of the data is from the survivors of Hiroshima and Nagasaki. We are just trying to be as careful as we can.

DM: How much radiation exposure do we get from the sun?

MH: Total background radiation gives everybody about 3 mSv per year from the Earth, the Sun, and man-made sources. The biggest contributor is radon gas (2 mSv/year).

During a 7 hour airline flight, we are exposed to more cosmic radiation because there is less protective atmosphere. This is about the same as a chest x-ray.

DM: That brings to mind the risk to pilots and crews.

MH: They are exposed to more radiation than the average person. They are not
regulated by any government oversight board or protection agency like radiologists are even though pilots are exposed to more radiation. Domestic airline pilots are exposed roughly an additional 2 mSv a year, but studies haven't shown that pilots get cancer any more than people who are not pilots.

DM: Of course radiation is also used to kill cancer.

MH: Yes, really high doses of radiation kill cells. The way that radiation
causes cancer in low doses is by damaging the DNA. Usually, cells repair DNA damage and all goes back to normal. But sometimes the DNA repair is faulty and that is how you can get cancer. The doses to treat cancer are very high doses. Unfortunately, one of the reasons we know that radiation does cause cancer is that people who were treated as children with high doses of radiation have a higher risk of other cancers later on.

In terms of medical imaging, we have no studies of people that just got CT scans and X-rays to say they have more cancer than those who don't have CT scans and X-rays. We can't do that study because the risks are so small it would take millions of people to study.

DM: What can the average patient take away from all this?

MH: Unfortunately, the lifetime risk of developing cancer is about 45% for men and 38% for women, which is scary in itself.

The increased risk from the average imaging studies is very small and theoretical at best. People argue about what it all means. In the end it is all about weighing the risks and benefits. My advice would be don't get a whole body CT without good reason, although the risk is low, because the potential benefit is also low. Versus someone who comes in to the ER after a car accident--their potential benefit is very high and the risk very low. In that case the risks of radiation exposure should not even be discussed.

You have to weigh the risks and benefits. The same way that if your doctor tells you to take an aspirin for general heart health. Aspirin has a laundry list of side effects yet we know aspirin prevents heart attacks and strokes and the benefits outweigh the risks. That approach to a CT or chest X-ray should be the same: If the potential benefit is greater than the potential risk, it is worth doing. The www.xrayrisk.com website allow users to quantify this risk.

DM: GE is the sponsor of your website.

MH: Yes. I did this as a research project and needed funds for programming. I contacted GE and they were willing to help me get it up and running but they have no control over the site content or management.

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Read More About This

In addition, read more recent news about this important topic on DOTmed.com:
-CT Scans: Too Much of a Good Thing Can Be Risky (RSNA)
http://www.dotmed.com/news/story/8645
-Be Alert to Radiation Risk From Medical Tests (Harvard Heart Letter)
http://www.dotmed.com/news/story/8622
-Self-Referral Leads to Increased Radiation Exposure, ACR Confirms
http://www.dotmed.com/news/story/8356
-Cardiac CT Radiation Doses Can Be Lowered by 39 Percent in Most Patients
http://www.dotmed.com/news/story/8698


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