Questions and Answers for Physicians About Medical X-Rays
What are the risks from ionizing radiation associated with medical x-rays?
There are two different types of risks, stochastic and deterministic. Stochastic effects are those in which the probability (not the severity) of the effect depends on dose. Examples of stochastic effects include cancer and genetic effects. The time between radiation exposure and the clinical presentation of these effects generally is measured in years to decades. Deterministic effects have a threshold and are those in which the severity of the effect varies with the dose. Examples of deterministic effects include hair loss, skin burns, cataracts, diminished fertility, and bone marrow suppression.
Deterministic effects require significantly higher doses than stochastic effects and usually are only associated with repeated or very prolonged interventional fluoroscopic procedures. The time between radiation exposure and the initiation of these effects generally is measured in days to years. Of the two types of effects, the stochastic is the one of most concern as a public health issue. While the chance of inducing a cancer from one or more radiographic, CT, interventional fluoroscopic, or nuclear medicine studies is generally quite low for any individual, the fact that tens of millions of examinations are being performed each year places a significant number of people at risk.
Which examinations are most likely to give my patient high doses of radiation?
While every x-ray examination will subject your patient to some amount of radiation, the ones mostly likely to subject your patient to a high dose of radiation are:
- computed tomography (CT), especially of the abdomen and pelvis with and without contrast;
- interventional fluoroscopic examinations, especially complicated cardiac and neurological procedures; and
- some nuclear medicine examinations, such as stress cardiac studies.
In addition, patients who undergo repeated examinations are at increased risk of receiving high radiation doses.
What can I do to ensure that I get a complete radiological history from my patients?
Just as you ask your patients for a complete list of the medications they are taking, you should ask them for a list of all the radiographic examinations they have had. This will serve three purposes. First, it will help you determine what tests they have already had that might help in the diagnosis of their current problem. Second, it will help you decide which tests they still need to have. Last but not least, it will give you an indication of the cumulative radiation dose your patient has received over his or her lifetime. Typical doses associated with various exams are listed in Table I of the following web page: http://www.fda.gov/cdrh/ct/risks.html.
What is the FDA doing to help lower medical radiation exposure?
FDA works to protect the public from unnecessary radiation exposure by establishing performance standards for radiation-emitting products and monitoring the safety of radiation-emitting products currently in use. For example, FDA regulations require that all fluoroscopy equipment built after June 10, 2006, contain a number of dose-reducing features, including:
- a display indicating the dose the patient is receiving for the procedure;
- an audible indication of each five minutes of fluoroscopy time; and
- a “last-image-hold” capability allowing the fluoroscopist to review the last image on the fluoroscopic monitor without having to radiate the patient.
FDA also collaborates with other organizations developing international safety standards that incorporate dose-reduction technologies in various radiological equipment, including computed tomography.
Finally, FDA collaborates with other organizations to develop and disseminate information that will help medical imaging facilities, health professionals and others minimize unnecessary radiation exposure.
What are manufacturers doing to limit radiation or facilitate dose monitoring?
Manufacturers of CT units are developing and including automatic exposure controls (AEC) in their newer units. An AEC automatically adjusts the amount of x-ray exposure to the patient to optimize the final CT image. Manufacturers of fluoroscopy as well as CT units are also including hardware and software to make the collection of dose information easier and more automatic.
Are there any population sub-groups that are more at risk from radiation?
In general, the younger the patient, the greater the risk of radiation-induced cancers later in life. Because of this, additional consideration should be given before ordering any radiographic examination on children and pregnant women.
Also, women who are exposed to the same radiation doses as men are at a somewhat higher risk of developing cancers later in life.
What should I tell my patients about ways they can reduce their risks from medical x-rays?
In most cases, the benefits of having a medical x-ray exam far outweigh the risk of not having the exam because of concerns about radiation. Forgoing an exam may result in not obtaining appropriate clinical diagnosis or treatment.
But patients can reduce unnecessary exposure to radiation by informing you and the radiology facility about previous examinations they have had. They can also ask about procedures the facility has in place to ensure that the examination is being performed consistent with ALARA (as low as reasonably achievable), including being shielded during the study. Female patients should let the radiologist or x-ray technologist setting up the procedure know in advance if they are pregnant or think they may be pregnant.
What are common occupational hazards associated with performing medical imaging procedures?
Risks include a small increase in the chance of developing cancer later in life. In a few interventional procedures, where there may be high radiation doses to the lens of the eye or to the skin, there are risks, respectively, for developing cataracts and of injury akin to a skin burn.