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John W. Gofman, M.D., Ph.D., Professor Emeritus,
Molecular and Cell Biology, Univ. Calif. Berkeley
and Egan O'Connor, Exec. Director, CNR and XaHP.
XaHP Document 106, September 2000
XaHP: The X-rays and Health Project.
An educational project of the
Committee for Nuclear Responsibility.
Part 1. The Chance of Having an X-Ray This Year
The U.S. Food and Drug Administration makes this estimate on its website, March 2000: Seven out of 10 Americans will get a medical or dental x-ray "picture" this year (www.fda.gov/cdrh/consumer/xraybrochure.html). "cdrh" stands for "Center for Devices and Radiological Health."
Sooner or later, you or a family member is very likely to contemplate an x-ray, due to a medical or dental problem or due to an accident. X-rays are sometimes used during surgery, not for diagnosis, but to determine the location of catheters, needles, and other equipment.
Children have a higher risk of x-ray-induced cancer than most adults. Some people have a higher risk at any age, due to inherited vulnerabilities to mutagens --- such as one or more defective repair-genes in every cell.
Two types of x-ray imaging procedures which generally (not always) deliver the highest x-ray doses are fluoroscopy and CT exams (XaHP Doc.102). The American Cancer Society has stated, "Fluoroscopy delivers larger doses of x-ray than that used in standard films. If there is an alternative means of making a diagnosis, fluoroscopy should be avoided" (ACS, Jan. 1992, "Guidelines for the Wise Use of Medical X-Rays," Item 2900 on the ACS "Cancer Response System").
Part 2. Some Guidance about Fluoroscopy
Each fluoroscopic machine has variable dose-rates per minute. The FDA set a maximum rate of 20 Roentgens/min for equipment manufactured after May 1995. Older machines are capable of delivering unlimited exposure rates, unless the service engineer has been asked to install a limit --- which can be done on the older machines. According to Joel E. Gray, Ph.D., who is a leading figure in medical physics, an optimized fluoroscopy system delivers 1 to 2 Roentgens (R) per minute, with a maximum rate of 10 R/min (Gray 1998a, p.62).
Suggestion: Ask if fluoroscopy will occur during any part of your diagnostic or surgical procedure. Find out in advance what limit (if any) is set on the machine's dose-rate in the "High Level Control" mode. If no one knows, think hard.
A fluoroscopic system which facilitates reduced dosage includes several features, described below.
A very desirable feature is a "display," adjacent to the fluoroscopic monitor, showing the fluoroscopist the actual exposure rate and the cumulative dose in "real-time." Even better are the systems which make a permanent record of this information. Also available are systems which emit an audible warning when exposure rate and/or cumulative dose reaches a "notification" level, pre-set before the procedure begins.
The feature called "freeze-frame" or "last-image hold" is very desirable, because it provides a good (but static) image which can be examined without keeping the x-ray beam on.
Very desirable, too, is the "pulsed-progressive" feature, which does not use a continuous x-ray beam. Instead, it pulses the x-ray beam on for a few milli-seconds at a time, which reduces dose and produces sharper images, according to Gray 1998b (p.67).
Also desirable is a continuously adjustable, circular "collimator" (beam adjuster). Otherwise, with an image receiver which is circular, a rectangular x-ray beam necessarily irradiates more area of the patient than needed (Shope 1997, p.14).
Part 3. Some Guidance about CT Exams
Suggestion: Ask if you can have an exam which does not use "overlapping slices." Overlapping slices mean that the overlapped areas receive twice the dose.
Suggestion: If you are thin, or if your child will have the exam, try to ascertain that the operator adjusts the exposure according to size. There is no need for smaller patients to receive the same dose as a thick person.
Suggestion: Ask if the procedure involves a "contrast agent" --- a substance which is often needed to obtain images of natural tubes such as the blood vessels, esophagus, upper and lower gastro-intestinal tract, and urinary system. If the answer is "yes," the exam may be done twice --- with and without the contrast agent. You might ask if the exam truly needs to be done both ways. If one will suffice, your dose will be cut in half.
Three-dimensional imaging without x-rays is sometimes available. In 1995, a member of Britain's Royal College of Radiology stated that MRI (Magnetic Resonance Imaging) can do almost everything now which CT (Computed Tomography) can do. Fairly soon, 3-dimensional images from ultra-sound machines may also be a non-x-ray alternative in some circumstances.
Part 4. Teeth, Breasts, Testes, Shielding
Teeth: For dental x-rays, "digital" imaging (no film) can deliver considerably less dose than conventional imaging (films). We have seen claims that digital gives 60% less dose, even 90% less dose. We have no independent confirmation. (Each facility should do regular measurements, because true doses and assumed doses can be very different.)
Breasts: Females at any age should pay special attention to "chest" x-ray exams where the x-ray beam travels from front to back. If the exam can be done instead from back to front, the breasts will receive a much lower x-ray dose (about 5%). Breasts receive irradiation during exams of the heart, esophagus, ribs, lungs, upper spine, shoulders, etc.
Testes: During x-ray exams of the abdomen, pelvis, lower spine, hip, or thigh, males should try to keep their testes out of the x-ray beam (by shielding).
Shielding means covering (with a lead-lined cover) an area which is in the x-ray beam but whose image is not needed. Suggestion: Ask the x-ray technologist to show you the four corners of the area which will be irradiated. (Often, it is the full size of whatever standard film is being used.) Ask if any areas can be shielded, and if not, why not.
* Part 5. Do You Have Power as a Customer?
XaHP Document 104 lists several techniques which can reduce x-ray dosage, while still obtaining high-quality images. Patients who are willing to ask about such matters as peak kilovoltage, filtration, distance from the x-ray focal point to the patient, etc., will have additional ways to discern which x-ray practitioners in their area are more likely to give lower doses than others.
And what if your HMO or other health insurer does not permit a choice of x-ray practitioners? What then? Whenever customers (you) cannot take your business elsewhere, "market forces" are very weak.
There is no mystery about how to reduce doses, technically. What is lacking is leadership. If just a few thousand American radiologists would openly endorse the goal, their leadership (in our opinion) could reduce the average dose-level administered by other radiologists virtually overnight. Other kinds of x-ray practitioners would follow suit.
The leadership of radiologists, which we encourage, would provide the fastest, most efficient, and lowest-cost way to get the job done.
# # # # #
- Gray 1998a (Sept.), Joel E., "Lower Radiation Exposure Improves Patient Safety," in Diagnostic Imaging Vol.20, No.9: 61-64.
- Gray 1998b (Oct.), Joel E., "Optimize X-Ray Systems to Minimize Radiation Dose," in Diagnostic Imaging Vol.20, No.10: 62-70.
- Shope 1997, Thomas B., "Proposed Fluoroscopic Amendments," memo & letter March 18, 1997 to "Fluoroscopic X-Ray System Manufacturers, Users, and Other Interested Parties," from Dr. T.B. Shope, U.S. Public Health Service, Ctr. for Devices and Radiological Health, 5600 Fishers Lane, HFZ-140, Rockville MD 20857.
Leadership on dose-reduction was exemplified by the
American Cancer Society in a 1982 statement:
"The American Cancer Society firmly believes that any risk, no matter how small, should be reduced as much as possible and that radiographic equipment should deliver the lowest dose of radiation consistent with producing an optimal diagnostic image."
--- From pg. 228, "Mammography 1982: A Statement of the American Cancer Society," approved by the ACS Medical and Scientific Committee and Board of Directors. In "CA - A Cancer Journal for Clinicians," Vol.32, No.4: 226-230. July/Aug. 1982.