Medically reviewed by Michelle Goñi, MD, Susan Kerrigan, MD and Marianne Madsen
You’re worried. Your doctor wants to schedule a test that uses radiation. Maybe you’ve read about the risks. It’s important to not only understand how much radiation each test delivers but also how these amounts compare to the amount you are exposed to on a daily basis. Radiation is everywhere. Most of the time we don’t even think about it. So how much will you get in an X-ray, CT Scan, or some other test?
Really Radioactive
Radiation surrounds us. Energy from the sun pierces our atmosphere; it flows up from the ground in the form of radon gas. Atoms, the smallest particle of an element, have within their central core (nucleus) protons and neutrons. The nucleus is positively charged; negatively charged electrons revolve around the atom’s outer shell. If these protons and electrons are unstable, the atom sheds excess energy. This lets the atom achieve balance. Radiation is the name we give to the energy that the atom sheds.
Radiation is an “electromagnetic wave” because of its electric and magnetic fields. It travels at light speed. Unlike light, radiation can go through skin––illuminating what once could not be seen without surgery. Both the incidental radiation we’re exposed to every day and the kind used in medical devices is what’s called ionizing radiation. Besides penetrating tissue to illuminate hidden anomalies, these high-energy wavelengths can also damage DNA. Despite the body’s best efforts to repair the damage, some damage remains––leading to mutations that elevate cancer risk.
In a year, we are all exposed to around three millisieverts (mSv). If you live in Florida, where homes are more or less at sea level, you get about 1.5 mSv more per year than someone living in the mountains of Colorado. No matter where you live, about 2/3rd of your radiation exposure is due to the radon gas emanating from your house.
Discovered by accident over 125 years ago, the X-ray was the first step in medical imaging reliant on radiation to make what was once hidden visible. Getting a chest X-ray as an adult exposes you to about 0.1 mSv––the same as 10 days of natural background radiation. For that reason, most people who have the rare X-ray aren’t terribly worried. CT-Scans are different.
CT Risks
During a CT (computed tomography) scan, a patient lies down on a table before being transported within a large metal ring. As a machine whirls around the patient, X-rays are shot in bursts. Later, a computer can combine them into a 3-D image of bones, organs, tissues. The device is extremely useful in detecting early stage cancers. It also delivers a far larger dose of full-body radiation than an X-ray––up to 300 times as much. Although the machine was introduced in 1972, its use has accelerated in the 21st century. In 1980, just three million CT scans were used in the United States. Today it’s around 80 million. Although the U.S. leads the world with a per capita rate of 278 per thousand inhabitants, Iceland, Korea, and Turkey all log numbers above 225 per thousand. All that radiation has prompted concerns. Unfortunately, there is limited data on the long term risks of radiation––most studies were on survivors of the 1945 atomic blasts in Japan. Plus, there’s no denying the benefits of CT scans. Besides reducing the need for invasive exploratory surgery, studies support the notion that CT scan utilization led to improved outcomes after surgery, along with better treatments for everything from cancer to accidental injuries and trauma, so deciding on a CT scan is always a risk/benefit decision.
CT scans aren’t the only source of radiation that patients encounter. If you have a lumbar spine X-ray, you’ll receive around 1.5 mSv. Screening Digital Mammography gives patients 0.21 mSv. Nuclear imaging delivers 6.3 mSV for a bone scan and a high of 40.7 for a cardiac stress test (meaning it’s comparable to years, not days, of normal radiation absorption.) Yet despite the huge rise of CT scans, they increase the chance of developing fatal cancer to around one in 2000. During an average man’s lifespan, he faces a 44.9 % possibility of developing an invasive cancer (for women it’s 37.5%). Compared to the risk we all face, the slightly elevated possibility from medical imaging machines is small. Still, CT scans account for over three-quarters of the effective radiation dose delivered from all imaging procedures. This despite the fact that just 11% of X-ray-based examinations are CT scans.
Cancer risks are also far higher for pediatric patients who are subject to these devices. The solution is not to avoid ever getting a CT scan. Dangers from radiation are certainly less than the risk of metastatic cancer. Still, discuss the procedure with your doctor. You may be a candidate for an MRI that doesn’t depend on radiation. Above all, don’t demand CT scans or other tests just to confirm you’re healthy. The slim possibility of being rewarded by discovering an undetected tumor is not worth the radiation risk.
Written by John Bankston