plain HTML | ASCII text formats
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 102, September 2000
XaHP: The X-rays and Health Project.
An educational project of the
Committee for Nuclear Responsibility.
Post Office Box 421993
San Francisco CA 94142-1993.
Gifts are tax-deductible.
Part 1. A Tale of Two Views
According to the affectionate wife of a radiologist, "Radiologists see themselves as saving lives and doing no harm in the process. They assume that x-ray doses are not an issue, as long as their equipment is inspected twice a year. Doses are not what interests them. What interests them a lot is getting clearer images and faster images. And the people they listen to are the equipment salesmen and each other."
A reminder is appropriate: Radiologists are certainly not the only x-ray practitioners. Many internists, cardiologists, urologists, gastro-enterologists, orthopedists, chiropractors, dentists, and others do their own x-ray work. Moreover, according to a 1989 report (NCRP 1989, p.34): "In many office practices in the U.S., x-ray examinations are performed by persons with little or no formal training in the uses of x-rays or x-ray protection."
The personal comments of the radiologist's wife seem to be consistent with the published comments of Joel E. Gray, Ph.D., professor and medical physicist at the Mayo Clinic until his recent retirement to become a consultant. Dr. Gray is a world-class expert in obtaining high-quality x-ray images while minimizing x-ray dosage to patients and staff.
Is Dr. Gray concerned by insufficient attention to minimizing dose-levels during x-ray imaging?
Readers can judge for themselves, as we do. This document quotes (below) from Dr. Gray's 1998 articles entitled "Lower Radiation Dose Improves Patient Safety," and "Optimize X-Ray Systems to Minimize Radiation Dose" (Gray 1998a+b). Both articles were publisheed in "Diagnostic Imaging," a newsmagazine for x-ray professionals (www.dimag.com). XaHP Document 104 briefly describes several of the techniques recommended by Dr. Gray and by others for achieving major reductions in x-ray dosage, while retaining good image-quality or even improving it.
Part 2. "Most Imaging Professionals Are Not Aware ..."
Dr. Gray recommends that, "to reduce the potential incidence of induced cancers," it would make sense to concentrate first on the x-ray imaging procedures which account for the most dosage (Gray 1998a, p.63). Today, the higher doses in x-ray imaging usually, but not always, come from Computed Tomography (CT) and from procedures using fluoroscopy --- which is the use of a continuous x-ray beam to observe the motion of arteries, organs, catheters, or other equipment.
"Most imaging professionals are not aware of the high doses of radiation that CT produces. It is therefore essential to educate the imaging community and referring physicians about CT's high exposures. Although the use of this modality should not be discouraged where its benefits are clear, referring physicians should be aware that CT is one of the highest radiation-exposure exams in diagnostic radiology" (Gray 1998a, p.63).
X-ray doses to patients from CT exams are typically, but not always, about 10 times higher than from "conventional" x-ray images (UNSCEAR 1993, p.235/81).
Use of CT exams has been rapidly growing for 20 years, as cheaper and more powerful computers have made such exams faster. CT exams are one of several digitally-based x-ray procedures which produce images without using film.
The result? The images from such procedures can look the same, even when they are made from a large range of doses. Thus, if doses are not measured, x-ray practitioners who give high doses can be unaware of doing so. Techniques exist with which x-ray practitioners could make major reductions in the dose-levels delivered during many CT procedures (discussion in XaHP Document 104).
Part 3. "Many Users of Hospital Fluoroscopy Equipment Do Not Understand the Basic Principles ..."
The other biggest source of dose in x-ray imaging is fluoroscopy. Dr. Thomas Shope, an expert at the U.S. Public Health Service, reports that "Over the past 20 years, there has been a substantial increase in the use of x-ray fluoroscopy as a visualization tool for a wide range of diagnostic and therapeutic procedures" (Shope 1997, p.i).
According to Gray, "Many users of hospital fluoroscopy equipment do not understand the basic principles of radiation protection and proper use of fluoroscopic equipment. It is necessary that physicians receive basic education about radiation and fluoroscopy before using the equipment. The [hospital's] Radiation Safety Committee can credential individuals who have obtained the appropriate education, and the hospital can grant privileges based on credentials. Continuing education should be required to maintain physicians' credentials and privileges" (Gray 1998b, p.70).
Part 4. "If You Don't Know What Your Exposures Are ..."
Healthcare facilities nationwide are periodically accredited by the Joint Commission on Accreditation of Healthcare Organizations (JCAHO). The JCAHO is an independent not-for-profit organization whose mission is "to continuously improve the safety and quality of care provided to the public ..." (www.jcaho.org). The JCAHO used to require that x-ray exposures at accredited facilities be measured and compared with national survey data (such surveys are described in XaHP Document 103). On the key role of measurement, Dr. Gray comments to x-ray practitioners:
"If your exposures have not been measured recently, you cannot be sure what exposures you are using. And if you don't know what your exposures are, you don't know if you are doing a good job" (Gray 1998a, p.61). Dr. Gray stresses that dose-reduction techniques not only reduce the risk of causing cancer, but they can sometimes produce better images.
"It is time for the radiology imaging community --- radiologists, medical physicists, and technologists --- to take the necessary steps that will optimize x-ray imaging systems to reduce radiation exposures and improve image quality" (Gray 1998b, p.70). Dr. Gray's articles describe steps which can cut dose by 5-fold under several circumstances.
Part 5. "Useless Radiation": Inexpensive to Eliminate
The term "useless dose" (sometimes called "wasted radiation") can be defined as x-ray dose, given to patients during x-ray imaging, which is not required in order to achieve the medical benefits of the x-ray imaging but which needlessly increases the patients' risk of an x-ray-induced death later on.
Radiologists in Toronto, Canada, participated in a dose-reduction program twenty years ago (Taylor 1979). They invited a team of medical physicists (health physicists) to observe their actual practices, to measure doses, to teach low-dose techniques, to tune-up the existing equipment, and to ensure proper processing of exposed films.
The result? The experiment demonstrated that dose from diagnostic radiology could be reduced "by a factor of at least 3 with little work and by a factor of 10 or more if all conditions are optimized" (Taylor 1983, p.557). These achievements were obtained without purchases of major new equipment, and without reduction in the quality of x-ray images.
This is still the case, according to Dr. Gray many years later: "Techniques for reducing radiation exposure in angiography [imaging of the vessels] and fluoroscopy are relatively simple, inexpensive, and easily applied to general radiographic imaging" (Gray 1998b, p.62). XaHP Document 104 describes several of the techniques identified by Dr. Gray and by others for achieving major reductions in dosage, while retaining good image-quality or even improving it.
Fortunately, elimination of useless doses from medical x-ray imaging very seldom requires expensive new equipment. Instead, it requires the reality-check of frequent dose-measurements (which are simple and inexpensive to make) and it requires better technique (which requires motivation).
Part 6. The Simplicity of Dose-Measurement
The entrance dose of x-rays is the dose received at the body's surface, where the x-ray beam enters. The exit dose, which is what results in an image, is very much lower (sometimes about 5% of the entrance dose). The body absorbs the difference between the entrance and exit doses.
It is both easy and inexpensive to measure the entrance dose of x-rays during an x-ray procedure. On the patient's skin, the x-ray technician just tapes a small crystal which responds to the x-ray dose. The crystal does not interfere with the image. These crystals are called TLDs (Thermo-Luminescent Dosimeters). If two x-ray images are made from different angles, two TLDs are used. After the x-ray procedure, the irradiated TLDs are sent to a "reading" machine which reveals the entrance dose. Commercial services provide and read TLDs for about eight dollars per TLD, for accounts using about 50 TLDs per month.
True doses, measured during actual procedures, sometimes differ many-fold from the assumed or calculated doses (Wochos 1977 + 1979; NCRP 1989, p.35). Unless x-ray practitioners periodically measure the entrance doses and compare them with assumed or calculated doses, they will not know what doses they are really administering.
# # # # #
- 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," Diagnostic Imaging Vol.20, No.10:" 62-70.
- NCRP 1989. National Council on Radiation Protection and Measurements, "Exposure of the U.S. Population from Diagnostic Medical Radiation." Bethesda MD: NCRP Report 100. 105 pages. The NCRP is a nonprofit organization funded by various groups including the Amer. College of Radiology, Amer. Dental Assn., Amer. Medical Assn., Amer. Nuclear Society, Radiological Soc. of No. Amer., US Dept of Energy, US Nuclear Reg. Commission, and others.
- Shope 1997, Thomas B., "Proposed Fluoroscopic Amendments," memo & letter March 18, 1997 to "Fluoroscopic X-Ray System Manufacturers, Users, and Other Interested Parties," from T.B. Shope, U.S. Public Health Service, Ctr. for Devices and Radiological Health, 5600 Fishers Lane, HFZ-140, Rockville MD 20857.
- Taylor 1979, Kenneth W. et al, "Variations in X-Ray Exposures to Patients," Journal of the Canadian Assn. of Radiologists Vol.30: 6-11.
- Taylor 1983, Kenneth W. "Diagnostic Radiology." Chapter 16 in The Physics of Radiology, Fourth Edition, edited by H.E. Johns and J.R. Cunningham. Springfield IL: Charles C. Thomas, publisher.
- UNSCEAR 1993. United Nations Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionizing Radiation: 1993 Report with Scientific Annexes. ISBN 92-1-142200-0. 922 pages.
- Wochos 1977, J.F. et al, "Patient Exposure from Diagnostic X-Rays: An Analysis of 1972-1979 NEXT Data," U.S. Food and Drug Admin., Dept. of Health, Educ. & Welfare, HEW Publication 77-8020.
- Wochos 1979, J.F. et al, "Patient Exposure from Diagnostic X-Rays: An Analysis of the 1972-1975 NEXT Data," Health Physics Vol.36: 127-134.
- XaHP Document 103, Variation. Gofman and O'Connor, "How X-Ray Doses Vary from One Practitioner to Another: Nationwide Surveys," X-rays and Health Project, POB 421993, San Francisco CA 94142-1993.
- XaHP Document 104, Techniques. Gofman and O'Connor, "Techniques for Reducing X-Ray Doses to Patients and Staff," X-rays and Health Project, POB 421993, San Francisco CA 94142-1993.
and can always be found at http://www.ratical.org/radiation/CNR/XHP/XRayAttention.html