Medical x-rays now account for about 15% of radiation exposure in the United States and the amount is growing. Intermountain Healthcare in Utah now has a program to keep track of the accumulated radiation given to patients with x-ray procedures.
So, what is the true story? We know the advances in CT scanners have transformed medicine — we can see internal organs that previously could only be viewed with surgery. Doctors can diagnose internal problems with much improved accuracy. But, we also know CT scans, like all x-ray tests, come with some radiation exposure. The true story is a large measure of good with a pinch of bad.
The bad aspect of radiation with medical imaging is the slight tendency to set off cancer. Not right away, but many years after the exposure. The slight increase in lifetime risk is much less than 1%. To keep it in perspective the lifetime risk of fatal cancer is about 25% (25 out of 100 people die of cancer). Clearly, other things besides x-rays are causing cancer. 15% of radiation exposure is from medical imaging, but 85% is from background radiation — natural radiation from our environment, the sun and the stars.
There are imaging methods that have no radiation. Those are MRI (very good and very expensive) and ultrasound (blurry and cheap). If MRI was fast and low cost it might do away with regular x-rays but research is a long way from that ideal.
At least for then next decade x-rays will be the work-horse for medical imaging. Below is a table listing the x-ray exposure for various x-ray procedures. A chest x-ray is one of the most common x-rays and fortunately one that takes very little x-ray radiation. So, other procedures are often compared to the chest x-ray, also seen in the last column of the table.
The milliSievert (mSv) is the measure of radiation dose. One chest x-ray gives about 0.34 mSv. That amount of radiation is what a person would normally accumulate in 52 days from background radiation alone. Radiation treatment intended to damage tissue (like cancer tissue) requires 20,000 to 60,000 mSv — medical imaging is not in that ballpark.
Review of CT scans suggests that 1/3 may have been unnecessary. For instance, a CT scan done because of a bump on the head without any symptoms except from the bump would be considered unnecessary. So, an unnecessary CT scan is unnecessary radiation. None of us want radiation without some benefit. This thought is in the spotlight now, especially in emergency rooms, where a lot of the unnecessary scanning happens.
It seems reasonable to keep a running total of radiation exposure from medical imaging. Use the above table add up the radiation from all imaging tests you have had — a good number to tell your doctor, especially when additional imaging is proposed. The question “is that imaging test worth the radiation exposure?” is certainly reasonable.