Susan M. Love, M.D. (surgeon), is Director of the Revlon/UCLA Breast Center at the University of California in Los Angeles, and is the author of the well-known book, Dr. Susan Love's Breast Book (Love 1995). We sent her a copy of this book's First Edition, with a personal note, on March 30, 1995. She was in San Francisco on May 19, 1995, to hold a press conference and to give a talk. At each occasion, people asked her about this book. Because both occasions were videotaped by people making a program about breast cancer, we learned of her comments.Part 1. Dr. Love: Looking Behind and Ahead
Dr. Love stressed two themes, which we will flag as # and ## below. The first comments are from the press conference:
"There is no question that radiation, especially in children, is dangerous, and we ought to avoid it as much as possible. But a lot of that stuff was unique to the period [1920-1960]. #, There is no question that it may be the cause of a lot of the cancer we are seeing right now. A significant amount, but not quite that high [75-percent]. ##, We can't do anything about the past. But we can do something about the pesticides and hormones that are being pooh-poohed now. There is not much we can do about the past." And then at the evening talk (Herbst Hall), Dr. Love said:
#, "I'm not sure that it's quite that high [our 75-percent estimate], but I'm sure that a lot of the breast cancer we are seeing now can be explained by that. Back when we were kids, they were using radiation for all kinds of things, and people were not aware of the risk ... We used radiation for everything ... We were shrinking thymus glands with radiation ... People with TB were getting checked with x-rays all the time ... Even mastitis [was treated with radiation]. All of those people have a higher risk of breast cancer later on. So there is no question that it does explain some of the increase. I'm not sure I'd go as far as saying 75 percent." She continued:
##, "And we're not using radiation quite as liberally now as we did. We still could probably be more cautious, but I think that we don't do those things anymore, and what we need to focus on even more are the things that our daughters are being exposed to that will be causing breast cancer 20 or 30 years from now."
From the doubly-flagged "##" comments, it seems that Dr. Love considers overdosing by x-rays to be a past problem, not worth attention from her or from other breast-cancer activists. This is consistent with her 1993 "Commentary" in JAMA --- a "Commentary" in which she repeatedly and admirably stressed the need to focus on prevention of breast-cancer. She reported (Love 1993) that:
"Women around the country want breast cancer eradicated. They want research into the causes of breast cancer and they want to know how to prevent this killer. How can we achieve this goal?" Dr. Love suggested various actions (e.g., more research into the possible causal role of pesticides and chlorinated compounds). She neither mentioned radiation as a cause, nor reduction of radiation exposure as a guaranteed way to prevent a share of the future cases.
The assumption is very common, that current medical uses of radiation will make no significant contribution to the future incidence of breast cancer. Such a consequential assumption deserves a reality-check (Parts 2 and 3, below).Part 2. Reality-Check: Some growing Aspects of Medical Radiation
Although we will show, below, that some aspects of medical radiation have been growing since 1960, there is nonetheless a high probability that average breast-dose per female (USA) has decreased since its peak, especially for children. That is very good.
But it certainly does not follow automatically that x-ray overdosing has become a problem too trivial for solution by women "who want breast cancer eradicated" and who "want to know how to prevent this killer."
2a. The New, the Old, and the Opportunity
The hasty assumption, that radiation overdosing is a past problem, may be partly our fault. We provided a list in Chapter 37 of many past uses of the x-ray which no longer occur. And we pointed out that, per diagnostic radiograph, risk has been reduced by irradiating smaller areas (p.146). Faster films and better equipment have also helped to reduce dose per examination (pp.145-146).
But, at the same time, there are many more examinations per 1,000 people ... and there are several new types of breast-irradiating examinations which did not occur in the 1920-1960 "past" ... and most of the "old" breast-irradiating exams continue.
The net effect is very probably an average breast-dose lower now than it was during the 1920-1960 period (especially for children), and so what? Large additional dose-reductions are not only readily feasible (as we will show in Part 3), but such additional dose-reductions are also guaranteed to prevent a share of future breast-cancers (as we have shown in Chapter 45). The title of this book is no mistake. Our message is that, collectively, women and their families have the opportunity to have less radiation-induced breast-cancer in the future, if they make that choice.
2b. Some New Breast-Irradiating Uses of Radiation in Medicine
o - Mammography. Mammography used to be rare. It is not even included in Chapter 39's Master Table. Now women are urged to have a mammographic exam every year, after they reach age 50, and many women want to have them at much younger ages, too. A controversy rages over such screening below age 50. In the affluent countries, the average annual number of mammographic exams per unit of population approximately tripled between the 1970-1979 and 1985-1990 periods (UNSCEAR 1993, Table 8, p.283). In 1990, the U.S. Congress instructed Medicare coverage to include a mammogram every two years for women age 65 and beyond (ACS 1994, p.21).
How many women today (USA) have screening mammograms per year? We have two rather different estimates. The higher estimate: Approximately 18.6 million screening mammograms per year --- or 39 percent of women ages 40 to 79 (from UCSF 1995, p.3). The lower estimate: Approximately 12 million women (USA) have a screening mammogram each year --- allegedly 25 percent of the symptom-free women who are "currently eligible" (Khalkhali 1995, p.38).
Presently, "about 5 percent of screening mammograms are positive or suspicious, and of these, 80 to 93 percent are false positives ..." (Wright 1995, p.29, 31).
If the average absorbed dose per mammographic exam is about 0.2 rad (0.2 centi-gray), and if all women decide to have annual mammograms, the annual average breast-dose from this source alone would become almost half what it was in "the past," from all sources combined, for those ages (Master Table). If the average absorbed dose per exam were to fall to 0.1 rad, it would still amount to an appreciable fraction of total dose from all sources in "the past."
o - X-Ray-Guided Breast Biopsies (stereotactic needle biopsies). This non-surgical technique uses x-rays from different angles and a computer to plot the exact location of the suspicious area, before the needle is inserted. Several x-rays must be taken (a minimum of five, for one popular system), but only part of the breast is irradiated. One woman whose biopsy required eleven x-rays told us that, when she inquired about the total radiation dose, she was told 1.3 rads. She added, "I was also told that I was the first patient who ever asked them!"
We do not know how many breast biopsies per year are done this way, or the typical x-ray dose. By contrast, the number of surgical excisional breast-biopsies each year (USA) is estimated as follows. "In this country, we perform 750,000 and possibly a million open surgical biopsies, removing an abnormality found on the physical exam and/or mammography. Clearly, the majority of people who do have that procedure do not have cancer," says Joseph P. Crowe, Jr., M.D., director of breast services at the Cleveland Clinic Foundation (Crowe 1995, p.5). Referring to all breast biopsies combined, Dr. Iraj Khalkhali, chief of breast imaging at the Harbor-UCLA Medical Center, asserts that "only one out of four to six breast biopsies is positive for breast cancer" (Khalkhali 1995, p.38).
o - Scinti-Mammography. This is a diagnostic technique used experimentally by the Nuclear Medicine Division of the Harbor-UCLA Medical Center in Torrance, California; it is now in clinical trials at various institutions. Dr. Iraj Khalkhali, chief of breast imaging at the Harbor-UCLA Medical Center, is an enthusiast for it. With its further testing and evolution, he hopes that scinti-mammography may reliably distinguish dangerous from benign situations in non-biopsied women, and that "a large number of breast biopsies can be safely reduced" (Khalkhali 1995, p.38).
Patients are injected in the arm with 20 milli-curies of the radioisotope Technetium (Tc) 99m, SestaMIBI. The radiological half-life is a little over 6 hours. Breast images are taken 5 and 60 minutes after the injection (Khalkhali p.35). "There is no significant risk or discomfort to the patient. Compression of the breast is not required and the radiation risk is miniscule," according to Khalkhali (quoted in Harbor 1995).
The average dose to the whole body (including both breasts) per scinti-mammogram is 0.3 rad, with a dose of 3.0 rads to the large intestine (Khalkhali 1995, p.34-35). Since Tc-99m emits a gamma of about 140 KeV, the corresponding doses in our "medical rads" would be somewhat lower than 0.3 rad and 3.0 rads. Reduced or not, any dose to the whole body is very much more serious than the same dose to the breasts alone. Nonetheless, women have every right to choose an option like this, if they prefer it to the alternatives.
Potential alternatives also under development include BBE: Breast Biophysical Examination. BBE is a non-invasive, electrical method of examination, which distinguishes cancerous tissue from non-cancerous tissue after a suspicious area has been detected by mammography or physical examination. BBE, which itself involves no ionizing radiation, is being evaluated at multiple institutions, under the leadership of Joseph P. Crowe, Jr., M.D., director of breast services at the Cleveland Clinic Foundation. Crowe's opinion is that initial breast screening by BBE may become possible someday, but not soon (Crowe 1995, p.5, p.17).
o - Breast Irradiation From Computed Tomography, or CT Scans. In the affluent nations, the increasing use of CT scans is remarkable. The average annual rate per 1,000 population rose from 6.1 to 44, in the periods 1970-1979 vs. 1985-1990 (UNSCEAR 1993, p.283, Table 8). For 1985-1990, the annual rate in the USA was about 14.5 CT exams per 1,000 population; in Australia, 30 per 1,000; West Germany, 35 per 1,000; Belgium, 50 per 1,000; and Japan, 97 per 1,000 (UNSCEAR, p.280-281, Table 7).
What share of CT exams irradiate the breasts? UNSCEAR (1993, Table 14, p.297) provides one clue: In Britain (UK) in 1989, about 12 percent (because 0.7 % are thoracic spine exams; 7.9 % are routine chest exams; 4.0 % are mediastinum exams).
And what about doses to the breasts? An indication comes from Table 15 of the same source (p.297). In Japan, CT scans of the chest deliver an average absorbed dose to the breasts of 1.6 rads (15.9 mGy), with a range of 0.87 rad to 4 rads.
Doses to patients from CT scans are typically about 10 times higher than from "conventional" diagnostic examination by x-ray, according to UNSCEAR, p.235/81. However, there are special situations when CT scans give much lower doses than conventional x-ray techniques --- and UNSCEAR mentions myelography of the lumbar spine (p.235/81), and fetal doses from pelvimetry (p.237/95).
The trend in doses from CT scans is upward. Why? "The number of slices imaged on each patient has risen as the time required to perform scans and reconstruct images has decreased. However, since little change has occurred in the dose required per slice, the dose per examination is likely to have increased substantially" (UNSCEAR p.244/141, citing a report from Britain's National Radiological Protection Board: NRPB 1990). UNSCEAR continues:
"Indeed the average effective dose equivalent due to a body scan at the Mayo Clinic in the United States was 15.6 mSv (range: 9-60 mSv) in 1988 (Vetter 1991); in 1980, the comparable figure for the United States was 1.1 mSv (NCRP 1989)." We think this factor of 14 may need further documentation. (15.6 mSv is the same as 1,560 milli-rems. The term "effective dose equivalent" is explained in Part 2c, below.)
For those who assume that the x-ray problem keeps diminishing, we will describe the more complex situation in UNSCEAR's words: "Some examinations with higher doses, such as computed tomography, are becoming more frequent. At the same time, however, better equipment and techniques are allowing doses in other examinations to be reduced" (1993, p.267/302). And the net effect? "The total dose for all x-ray examinations per examined patient may be unchanged or only slightly decreased," with reference to the last decade or so (1993, p.242/130).
o - Breast Irradiation From Interventional Cardiac Radiology. Interventional radiology refers mainly to the use of fluoroscopy to guide the passage of needles, wires, and catheters, or to localize renal stones in lithotripsy, or to infuse pharmaceuticals in specific locations. Such uses, which are not purely diagnostic or directly therapeutic, are called "interventional."
In discussing fluoroscopy, UNSCEAR confirms that "The greatest radiation dose to individual patients in fluoroscopy is associated with imaging of the heart (interventional or otherwise)" (1993, p.233/71). Such imaging of the heart almost inevitably irradiates parts of the breasts.
Although cardiac catheterization was developed and used well before 1960, even on children, its use has increased (not decreased) since "the past" 1920-1960 period. The increase accompanies some spectacular developments in surgical repair of congenital heart defects and in repair or supplementation of clogged coronary arteries --- already mentioned at pages 183-185, and 213-214. The duration of fluoroscopy can be very long --- 22 minutes on the average for heart catheterization (p.214), and sometimes lasting long enough to cause serious skin injury (p.184 and p.216)
"Potentially very high doses" are associated with the dilation of cardiac vessels by percutaneous transluminal cardio-angioplasty (PTCA). In an Australian study of this procedure, skin doses ranged from 100 to 500 rads (UNSCEAR 1993, p.233/71). "The number of PTCA procedures in the United States increased to an estimated 400,000 in 1990" (p.232/69). That's just one cardiac procedure.
Although modern fluoroscopy equipment does not put out the highest doses per minute listed in our Index (see Fluoroscopy: output), the maximum rate has been reduced to 20 rads per minute only recently (p.185). UNSCEAR remarks, realistically, that "modern equipment may also have a potential for high doses ... For instance, high-level fluoroscopic boost options for image enhancement can contribute to high doses and may be easily activated, e.g. by a simple foot pedal" (1993, p.232/67). Anecdotally, we have heard various physicians characterized as "heavy on the pedal."
o - X-Ray Examinations In Neonatal Intensive Care Units. By and large, the diagnostic x-ray examinations given to infants are not new. What is new is the larger number of premature and congenitally challenged infants who are now surviving and receiving such x-rays.
o - Nuclear Medicine (the injection or ingestion of radio-nuclides for diagnostic and therapeutic purposes). As already illustrated by the discussion of scinti-mammography above, a radio-nuclide inserted into the body, because of a problem or suspected problem in a single area, is going to irradiate additional organs even if it ultimately concentrates in just one.
Thus, the breasts receive irradiation from uses of nuclear medicine which are totally unrelated to breast disorders. In the affluent countries, about 30 percent of nuclear medicine exams are of bone, 20 percent of lung, 15 percent of the cardiovascular system, and 15 percent of the thyroid (UNSCEAR 1993, p.324, Table 32).
The practice of nuclear medicine is a "new" use of radiation in medicine. Except for a few naturally occurring radio-isotopes and some produced on cyclotrons, there were virtually none available to medicine until after World War Two. The practice of nuclear medicine is one which has increased, not decreased, since "the past." Indeed, the number of such exams per thousand people doubled in the USA between 1972 and 1982 (p.256). The annual rate is about 28 diagnostic nuclear medicine exams per 1,000 population (about 7 million annual exams per 250 million people, USA).
New uses for nuclear medicine (including pediatric uses) and new techniques in nuclear medicine continue to develop. For example, "Single photon emission computed tomography has evolved rapidly since the early 1980s, when it was still rare. Not only is it now a standard method for tumour localization, but it is also used in a variety of applications, such as functional brain studies, cardiac studies, bone imaging and abdominal imaging. It can also be used in conjuction with labeled monoclonal antibodies" (UNSCEAR 1993, p.255/216).
2c. A Warning about "Effective Dose Equivalents"
UNSCEAR offers a very rough estimate that diagnostic nuclear medicine already adds about 10 percent to the population dose from diagnostic medical x-rays, worldwide (1993, p.257/229). For this estimate, and for many others, UNSCEAR relies on a dosimetric calculation called the "effective dose equivalent." Beware.
The word "effective" associated with any dose-estimate should grab the close attention of readers, regardless of their level of prior knowledge. Whenever that word is present, what follows is not a simple statement of dose (energy delivered per gram of tissue). Instead, the "effective dose equivalent" is a calculation which incorporates not only the quality of the radiation (for instance, high-LET vs. low-LET), but also a string of assumptions. UNSCEAR explains it as follows:
"The various organs and tissues in the body differ in their response to radiation. To allow for this, a further quantity, effective dose, is used. The equivalent dose [in rems or sieverts] in each tissue or organ is multiplied by a tissue weighting factor, and the sum of these products over the whole body is called the effective dose. The effective dose is an indicator of the total detriment due to stochastic effects in the exposed individual and his or her descendants" (p.12/69). And what is the input for those "tissue weighting factors"?
The International Commission on Radiological Protection "takes account of the attributable probability of fatal cancer in different organs, of the additional detriment from non-fatal cancer and hereditary disorders, and of the different latency periods for cancers of different kinds. All these features are included in the selection of weighting factors for converting equivalent dose into effective dose" (p.13/77).
The concept of evaluating "total detriment" is attractive. The big problem is the current quality of the evidence required to do it. Because the existing evidence for such tissue weighting factors is thin to really non-existent, we regard the "effective dose equivalents" as a step very likely to introduce large and needless errors into this field at this time. In our opinion, whenever a table or piece of text provides only "effective dose equivalents" and no actual doses, it is useless --- no matter how well intentioned.
2d. Reminder about Some "Old" but Enduring Breast-Irradiators
By 1960, almost all of the therapeutic uses of radiation, for treatment of non-malignant conditions, had been discontinued --- but the "old" diagnostic uses of x-rays (including fluoroscopy) had certainly not stopped. Conditions and diagnostic examinations, fully or partially irradiating the breasts, include (alphabetical order):
o - Barium Swallow. The patient swallows a barium contrast medium, which shows up as white on films or on a fluoroscopic screen, as it moves from lips to stomach. This exam necessarily exposes part of the breasts --- and almost all of the breasts, when a wide field is used without shielding.
o - Cardiac Problems Which Are "Watched" With Repeated X -Ray Images Or Fluoroscopy. Patients who are born with a congenital heart problem are not always fixed by surgery. Sometimes they are "watched" with repeated x-rays or fluoroscopies throughout their childhoods. Of course, we are not critical of such uses. We simply point out that they necessarily irradiate some lower parts of the breasts.
o - Cardio-Angiography (or Angiocardiography). This diagnostic exam of the heart shows its blood circulation, with the aid of a contrast medium administered by catheter, intra-arterially (or administered intravenously, for digital subtraction angiography). Fluoroscopy is used for 20-30 minutes, typically with the beam traveling from back to front, and about 20 still-pictures are made from front to back (Gofman 1985, pp.199-202). Inevitably, some lower parts of the breasts are irradiated too. UNSCEAR 1993 (p.233/71) confirms, that "Skin doses in cardiac angiography often approach 1 gray" (100 rads, or 100 centi-grays).
o - Cervical Spine (neck region). X-ray pictures of the cervical spine have typically extended 6 centimeters (over 2 inches) below the sternal notch, and thus they irradiate upper portions of both breasts, unless measures are taken to exclude them.
o - Chest X-Rays, Routine. When newborn babies need such exams, the pictures are usually taken with the x-ray beam traveling from front to back. Thus, the breasts receive almost the full force of the beam. However, front-to-back views are generally not used for examining older infants, children, and adults. The common chest exam includes one back-to-front view and one side-to-side view. Entrance surface doses today are in the range of about 0.015 to 0.030 rad; only a small fraction of the entrance dose reaches the breasts.
o - Chiropractic Full-Spine Exams. Such exams necessarily irradiate at least parts of the breasts.
o - Fluoroscopy. Because fluoroscopy provides immediate information, and also entails no expensive film and film-processing, it is attractive to use. Just press the pedal. UNSCEAR acknowledges that fluoroscopy "results in much higher doses than those from radiography, and its prevalence is both uncertain and changing with time" (1993, p.19/129). Fluoroscopy is not a problem belonging just to "the past." Even in 1994, the United States Government was urging physicians to keep some records and to use basic precautions to prevent severe over-use (see pp.184-187; also pp.216-217). See also Upper Gastro-Intestinal Exams, below.
o - Lumbar Spine Exams. Unless precautions are taken, lower parts of the breasts are irradiated during such exams.
o - Pelvimetry. This exam irradiates the breasts of the female fetus in the womb. Is this exam just part of "the past"? UNSCEAR 1993 (p.246/155) cites one source (MacMahon 1985) to the effect that abdominal irradiation of women during pregnancy has been virtually replaced by other techniques. Replacement may be technically feasible, but in Britain, during the 1976-1981 period, at least 4 percent of all pregnant women were examined by x-rays, and maybe 12 percent --- according to UNSCEAR citing papers by Kendall 1989 and Gilman 1989.
o - Rib Exams. Unless precautions are taken, more breast-area than necessary may be irradiated.
o - Scapula Exams (Shoulder Blade). This exam irradiates only one breast, but the beam is usually front-to-back.
o - Scoliosis (Curvature of the Spine) Which Is Monitored With Repeated X-Rays (Chapter 21). We will return to this topic in Part 3, below.
o - Shoulder Exams. This examination irradiates much of one breast, but not all of it.
o - Upper Arm (Humerus). X-rays of the upper arm expose the outer breast, unless precautions are taken.
o - Upper Gastro-Intestinal Series ("Upper G.I."). Patients swallow a barium contrast medium, as they do for the Barium Swallow Exam. The Upper G.I. Series usually involves an appreciable amount of fluoroscopy, which varies from examiner to examiner, and from patient to patient. The examination usually irradiates lower parts of the breasts, unless precautions are taken. The annual rate of Upper G.I. Series in the United States is estimated at about 33 exams per 1,000 population (UNSCEAR 1993, p.281, Table 7). Since few of these exams are given to children, the annual rate for adults seems extremely high. Nonetheless, the annual rate is even higher in Canada (72 per 1,000) and in Japan (156 per 1,000).
o - Upper Spine Exams (Thoracic Spine) --- Especially Post-Injury Management. Upper spine examinations necessarily irradiate parts of the breasts. Unless precautions are taken, much of the breast-area is irradiated. After bad accidents and certain occupational injuries, such exams can go on for years and years, as noted in Chapter 37, Part 2. Like scoliosis patients, female children and adults who have had a serious back injury, followed by numerous x-rays, are at elevated risk of breast cancer.
2e. Not So Simple: Forces at Work in Opposite Directions
Three Forces in One Direction
Three forces have been operating to raise the absolute number of radiation-induced breast-cancers "put on the shelf" each year since 1960, for delivery later.
1. The annual number of x-ray examinations per thousand people has been rising in the USA (p.256, for hospitals). Such examinations are done mostly in hospitals (NCRP 1989, p.12). The annual total estimate for the USA (in-hospital + non-hospital), during the years 1985-1990, is 800 diagnostic x-ray examinations per 1,000 persons, excluding dental x-rays and nuclear medicine (UNSCEAR 1993, Table 6, p.279). And with reference specifically to the United States, UNSCEAR notes: "Some information indicates that the estimate could be an underestimate by up to 60%" (p.229/46). The growth in exams per 1,000 people is not deep in "the past." We speculate that such growth may be causally linked with growing insurance coverage.
2. At the same time that the number of radiological examinations per 1,000 population has been rising (Point 1), the total population itself has continued to rise. Population (USA) has doubled since 1940, the midpoint of our 1920-1960 study-period; see our Table 2. When both the total population and the annual exams per 1,000 people double, the absolute number of examinations per year increases by a factor of 4.
3. Several new uses of radiation in medicine have been widely introduced.
Three in the Opposite Direction
On the other hand, there are three forces operating to reduce the absolute number of radiation-induced breast-cancers produced each year (and delivered later):
(1) Most therapeutic uses of radiation for treatment of non-malignant conditions have been abandoned.
(2) Most of the "old" diagnostic exams which are still useful are given with lower doses now.
(3) Fluoroscopy is used less commonly, especially for children.
Is there anyone who can quantify the net effect of these six forces? We don't think so. Even the total number of exams given today seems very uncertain, and the collective breast-dose from CT Scans, fluoroscopy, nuclear medicine, plus all the other x-ray examinations, is simply unknown right now.
Like others, we assume that the annual person-rads of breast-dose, across all age-groups, has been falling in the USA for quite a while. But just a foggy notion about a probable "fall" is no basis for dismissing the opportunity to prevent a real share of future breast cancer by causing a big additional "fall" in breast-dosage --- a provable fall. So in Part 3, we will present evidence to show that this goal is highly realistic.Part 3. Reality-Check: Some Major Examples of Current overdosing
The more that medical x-rays are used in a nation, the greater is the aggregate impact of even small overdoses per use. The number of diagnostic medical x-ray examinations given annually in the USA is impressive. The approximate number each year is at least 200 million (perhaps 60 percent higher) --- an estimate which excludes 100 million diagnostic dental x-ray examinations per year and 7 million diagnostic nuclear medicine examinations per year (UNSCEAR 1993, p.275, Table 3; also p.229/46; for the years 1985-1990).
3a. What We Mean by "Overdose"
If needed medical information can be obtained with a lower total dose of radiation, then an overdose has been given. Overdoses should be separated into two distinct classes. One might be called "careless" and the other "evolutionary."
"Careless" overdoses are those which occur because of failures to maintain the existing equipment well, to process film correctly, to position patients carefully, to avoid unnecessary repeats, to avoid exposure of unnecessary areas, to use the dose-reducing techniques in the literature, to insist on careful training, etc. Several of these failures were mentioned already in connection with current fluoroscopy (p.186, pp.214-216) and with common radiography (pp.292-294). Additional evidence will be provided below.
Carelessness results in doses to patients 3 times, 6 times, 10 times higher than needed from specific offices and users --- but patients and referring physicians presently have no way of knowing from which offices and users.
"Evolutionary" overdoses are those which occur because no one has yet developed the techniques and equipment which could achieve even bigger reductions of routine breast dose. Such techniques have been willfully developed into a 30-fold reduction for mammography (Chapter 28, Part 2) and a potential 50-fold reduction for scoliosis examinations (Chapter 21, Part 2). These are models for what might be achieved in other examinations, if the effort were made.
"Where there is a will, there is a way." Unless a comparably serious effort is made for other examinations, it is probably fair to say that nearly 100 percent of x-ray exams (excluding mammography) are done today at doses higher than needed --- in short, are delivering overdoses of the evolutionary class.
3b. Role of Digital Computed Radiography in Dose-Reduction
First the good news, then the bad.
Technical developments like digital computed radiography have the potential to reduce dose. "The rapid development of more powerful yet cheaper computers is revolutionizing all imaging methods ... The transition to digital systems in industrialized countries is likely to continue" (UNSCEAR 1993, p.242/131+132). And:
"At present, 15%-30% of examinations are digital. Digital radiography uses large image intensifiers or photostimulable phosphor imaging plates. Chest examinations using digital techniques can produce substantial savings of time and money for film, chemicals and archiving. While the quality of the image with a large image intensifier is not as good as with full-size images on film, the difference can be small enough to be clinically negligible" (UNSCEAR, p.242/132). And:
"If fluoroscopy is not used, an image intensifier can reduce patient exposure to one third that of full-size images on film or, in situations like peripheral angiography, to one tenth" (UNSCEAR, p.242/132; also p.238/100). However:
"Persistent anecdotal evidence indicates that some of the dose reduction per image in computed radiography may be offset by a tendency of radiologists to obtain more images per patient than they would have done with conventional film/screen systems. Also, while over- or under-exposure shows up in conventional radiology as incorrect blackening of the film, considerable over-exposure can go undetected in a digital system unless exposure is specifically monitored" (UNSCEAR p.243/134). No matter how elegant the machine, it can be carelessly used with respect to overdosing.
3c. Dose-Variation for the Same Exam --- Not Just in "the Past"
Large variation of dose for the same x-ray exam is an indicator that overdoses are occurring. But one must not assume that the minimum dose in a range of doses is the best dose. If a dose is too low to provide useful information, then all of that dose is an overdose. Moreover, some variation in dose is unavoidable (for instance, due to the different size of patients). Of course, one can be quite confident that the average dose is providing useful information (or it would not be so frequent). Thus, doses far above the average are likely to be overdoses. And all doses below the average are much preferable, until they approach a useless extreme.
Situation in the USA
Very large dose-variations for the same x-ray examination have been recorded in the USA and are displayed on page 292, which includes the average doses. Although the table is not from 1995, it is not from deep in "the past" either. The data are from 1972-1974, and were acquired under the NEXT program. NEXT stands for Nationwide Evaluation of X-Ray Trends, now a co-operative program conducted by the federal Food and Drug Administration, Center for Devices and Radiological Health (Telephone: 301-594-3533) and the Conference of Radiation Control Program Directors (Telephone: 502-227-4543).
When we attempted to acquire a current version of the same survey, we learned that such surveys were discontinued long ago in the USA, due to "budget cuts" (which may mean "considered unimportant"). For the last decade, about 400 institutions report on only one examination per year.
With this reverse-trend in data collection, we are not surprised that UNSCEAR (p.229/46) is very uncertain even about how many examinations are given per year in the USA since 1985.
Variations Reported in Other "Level One" Countries
The UNSCEAR 1993 report sorts nations into four levels of health care. Nations in Level One are presumed to have the most health care per 1,000 population.
"Doses per examination vary by a factor of 10 or more, even in a single hospital," reports UNSCEAR 1993 (p.243/136), with reference to nations at "Level One." And: "Screen/film speed is the overriding cause of patient dose variation in the United Kingdom, and fluoroscopy time in gastro-intestinal tract examinations is the second biggest cause" (p.243/137).
Big variations also occur in CT Scans. "In computed tomography, the absorbed dose for a given examination varied by a factor of 3 in New Zealand, and a factor of 5 in Sweden and the United Kingdom. In Japan, the effective dose equivalent for the same examination varied by a factor of up to 3.5, depending on the scanner unit ... Panzer et al  noted even greater variation, by a factor up to 10, with 122 scanners in the Federal Republic of Germany" (UNSCEAR 1993, p.234/80).
Variable dosage from radiography applies to infants, too . "A study covering 11 member States of the European Community (Schneider 1992), which considered typical x-ray examinations performed on infants (abdomen, skull, chest, spine, pelvis), showed large variations in entrance surface doses, far greater than the known and expected variations for corresponding examinations of adults. The maximum entrance surface doses for the abdomen, skull, chest, and spine were almost 50 times higher than the minimum doses, and for the pelvis, a 76-fold difference was found. The study had been standardized on the size of the infant, so that no additional variation was introduced" (UNSCEAR 1993, p.237/98).
"Examination of infants and young children is not infrequent. The per caput effective dose equivalent to children in the Federal Republic of Germany in 1983 was estimated to be 30 percent of the effective dose equivalent to an adult" (UNSCEAR, p.230/58). UNSCEAR's Table 9 for 1985-1990 combines the findings for ages newborn through age 15, and reports that (in the "Level One" nations), children age 15 and younger receive about 6 percent of the CT Scans, 5 percent of the chest fluoroscopies, 7 percent of the chest photofluorography, 8 percent of the chest films; 11 percent of the abdominal exams, 3 percent of the Upper G.I. Series, 19 percent of the skull exams, etc. (pp.284-290, Table 9).
Dose varies also for chiropractic exams. For example, UNSCEAR (p.237/93) cites a 1989 survey in Manitoba, Canada, which found that "the ratio of maximum to minimum dose was as great as 23. This is similar in magnitude to the variations found in medical diagnostic radiology," at which point UNSCEAR cites NRPB 1986.
The existing evidence from the "Level One" nations points overwhelmingly to major variation in dose for the same exam --- an indication of serious overdosing.
Frequency of X-Ray Examinations in Some "Level One" Countries
UNSCEAR 1993 has provided estimates in its Table 6 (p.279) of the annual estimated rate of x-ray examinations per 1,000 population in 27 countries at "Level One." Just to show the range of exams each year per 1,000 population, for the years 1985-1990, we have selected several countries:
Belgium: 1,290 exams each year / 1,000 population.
USSR: 990 --- and all past data from the USSR is in doubt.
USA: 800 --- and UNSCEAR says it may be 60 percent higher (1,280).
New Zealand: 640
3d. Exams Which Are Repeated, or Have No Medical Basis
Total overdoses come from x-ray or nuclear medical exams which are repeated due to errors, or were originally done for no medical reason. No part of their radiation dose is medically necessary.
How many x-rays are repeated simply because the quality of the first films is unacceptably poor --- or because the first films are lost? According to Caufield (1989, p.230), the United States Bureau of Radiological Health estimated more than 10 percent, and she cited its 1978 estimate (Bureau 1978, p.70) which we have not seen ourselves. According to Laws 1977 (p.112), some earlier estimates suggest only 3 to 6 percent, but she says such estimates do not count repeats ("re-takes") which occur on a later day!
A high rate of retakes reflects a careless attitude toward overdoses --- but not necessarily by the radiologic technologists ("rad techs"). Even when competent and conscientious "rad techs" know how to make all the calculations, adjustments, and judgments to get a good image with the initial exposure, they may be working under time pressure. According to Laws (1977, p.118), workloads can be so unreasonble that competent technicians have too little time to set exposures carefully, to adjust the size of the x-ray beam properly ... or even to employ lead shielding to reduce unnecesary exposure, when such shielding would be appropriate.
Where such work-overloads are normal, they reflect a careless attitude by the bosses toward overdosing. Another cause of re-takes (and overdoses without re-takes) is a plain lack of adequate teaching. Only a careless attitude toward overdosing allows inadequate teaching on the topic to persist anywhere.
Sometimes even the first set of x-rays done on a patient is not primarily for a medical diagnostic purpose. "Improper purposes include impressing patients, showing insurance companies that the work has been done, obtaining evidence in case of malpractice suits, and justifying investment in x-ray equipment" (Caufield 1989, p.230, citing Dr. Lauriston Taylor, chairman emeritus of the National Council on Radiation Protection).
According to Caufield (p.230, p.231), the United States Bureau of Radiological Health estimated in 1978 that hospitals were giving more than 18 million unnecessary x-rays per year, and altogether, it estimated that one in five x-rays was unnecessary (Bureau 1978, p.69, p.70).
The practice of "defensive medicine" is a "hot topic" now, but even in 1977, Laws was quoting from the 1973 book, A Practical Medico-Legal Guide for the Physician (Gordon 1973, pp.66-67): "An excessive number of x-rays may be taken, but they are necessary to support the diagnosis and to protect the physician from a malpractice claim. A lay jury or judge often considers the examination incomplete without pertinent x-rays. The patients themselves frequently share this opinion ..." This opinion is particularly easy for patients to hold, if the cost of such x-ray exams is covered by insurance.
3e. Slow Adoption of Known Dose-Reducing Techniques
The slow adoption of known ways to reduce dose is a type of careless overdosing.
Rare Earth Intensifying Screens
UNSCEAR 1993 provides an example when it states (p.243/135) that "The use of rare earth intensifying screens is one of the more important technical developments leading to lower doses per examination. While such screens are by no means new, having been available since the early 1970s, they are not yet fully utilized in all relevant situations. For instance, sample studies indicate that fewer than 50 percent of the radiographic examinations in the United Kingdom were carried out with rare earth screens in 1986 (NRPB 1990)."
How much can use of such screens reduce dose? "Rare earth screen cassettes, which may reduce doses by 50-90 percent, are used in only about half of British hospitals; and only six carbon fibre x-ray table tops, which may reduce doses by a further 10-40 percent to both staff and patients, are currently being used for general radiography in Britain" (Dawood 1988, p.1277).
Dawood and his co-author are in the Department of Pediatric Radiology, Hospital for Sick Children, in London. They comment (p.1277):
"Most people accept the risk from a small dose of ionising radiation in return for the benefits of radiological diagnosis. They trust that the radiation dose will be the smallest possible. Such trust may, however, be misplaced: There is considerable variation in somatic dose for the same procedure among different hospitals. Dose reduction is of greatest concern for children ..."
With respect specifically to breast irradiation, Hull 1985 (p.1) provides a disturbing example of careless overdosing in the USA. We quote:
"Scoliosis, a curvature of the spine, is usually monitored with x-rays. The most frequent victims are adolescent females; about 80,000 female scoliosis patients are monitored with x-rays every year. These exams have traditionally been taken from the front, giving the greatest radiation exposure to the breasts ..." (See Chapter 21.) And:
"In 1979, researchers at Case Western Reserve University in Cleveland found that ... by shooting from the back, [they can] significantly reduce radiation exposure to the breasts. Special shields and filters further reduce dose. Yet these simple practices aren't being used. A recent survey by the FDA of 256 x-ray units found just 7 percent using breast shields and only 11 percent shooting from the back. The FDA found more than a 200-fold range in radiation dose."
At the very same time, a senior editor of the Journal of the American Medical Association told Hull, "There aren't people out there giving more radiation than is needed. All the radiation given for diagnostic procedures is the minimum amount that can be given and still get a good picture" (Hull 1985, p.1).
3f. Additional "Instant" Ways to Cut Some Doses a Lot
Children receive about 6 percent of CT Scans (Part 3c, above). Their dosage can be reduced to half, with "negligible reduction of image quality," when xenon detectors are replaced by ceramic detectors, according to UNSCEAR (p.238/101, citing Parker 1989).
Infants in neonatal intensive care units (or special care baby units) often receive multiple radiographs from a mobile x-ray unit --- most commonly to diagnose and manage respiratory difficulties. A study of one British hospital (John Radcliffe Hospital, Oxford) found that 7.8 percent of all live births went to such a unit (Fletcher 1986, p.165). Skin dose per radiograph of chest and abdomen was measured there at about 0.007 rad (p.165). The average number of such exams per baby was 6.5 (p.167), with half of the babies receiving only one exam, and with an average of 59 exams for babies requiring ventilation (p.169). See also Chapter 37, Part 2.
Faulkner and co-workers investigated two methods to reduce the dose to newborn infants, per x-ray examination from mobile units (Faulkner 1989). They were able achieve a dose-reduction of 37 percent by using a lead rubber adjustable collimator to restrict the area of the x-ray beam, and an additional dose-reduction of 33 percent by using a rare-earth film-screen combination. They say that the latter reduction could have been even larger if the particular mobile unit at hand had allowed more selection of tube current and exposure time, or if they had also used a rare-earth metal filter (p.232). The two tested methods, used together, cut the neonatal dose more than in half per x-ray examination.
General Radiology: The Film-Processing Opportunity
A very common cause of overdosing in "Level One" nations is incorrect processing of radiographic films. And it is very common in the USA, as a 1992 paper by Suleiman and co-workers shows. At the outset (p.25), these workers explain: "The consequence of underprocessing is higher radiation exposure and a degradation of film contrast" (p.25). And the higher radiation dose is not small. There is a great deal to learn from their survey, conducted under the auspices of the federal Food and Drug Administration.
Since 1981, the FDA has been monitoring processing speed of over 2,000 automatic film processors in hospitals, private offices, and mammography facilities, as part of the NEXT program (see Part 3c). The survey "revealed underprocessing at 33 percent of observed hospitals in 1987, 7 percent of mammography facilities in 1988, and 42 percent of private practices in 1989" (p.25) "The quality of processing, in general, may actually have deteriorated during the study period ..." (p.27).
The Situation at Hospitals
"A detailed analysis revealed that ... the underprocessing component [of the data] for hospitals increased from 18 percent in 1984 to 33 percent in 1987" (Suleiman 1992, p.27). "We can only hypothesize that the deterioration in processing quality in hospitals was in part attributable to cost containment efforts. We have been told on several occasions that hospitals frequently eliminated Quality Assurance technicians to reduce costs" (p.27).
At one hospital, "technical experts identified an inaccurate thermometer and incorrect developer temperatures as the reason for underprocessing. The processors were readjusted. Radiographic kilovolt peak values and photo-timers were readjusted, the average exposure was reduced by more than 50 percent, and image quality improved substantially" (p.28; emphasis added).
On the average, at hospitals which were underprocessing, "patients undergoing diagnostic radiographic examinations ... would have received an additional 45 percent radiation dose attributable to underprocessing" (p.27, emphasis added).
The Situation in Private Practices
The survey indicates that radiologists may do better than non-radiologists (excluding chiropractors), and that non-radiologists may do better than chiropractors. The 1989 survey of abdominal radiography showed that 25 percent of radiologists in private offices (total sample of 4), 33 percent of non-radiologists (total sample of 82), and 48 percent of chiropractors (total sample of 143) were underprocessing (p.27).
The 1986 and 1989 surveys of private practices showed that, where underprocessing occurred, the average radiation exposure was 67 percent higher than necessary (p.27).
The Situation in Mammography Facilities
Meanwhile, mammography centers were performing better and better. In 1985, underprocessing occurred in 18 percent. In 1988, the percentage had decreased to 7 percent (p.27).
The Big Lesson, Thanks to Suleiman and Co-Workers
The big lesson comes from comparing performance at private offices and hospitals with performance at mammography centers. The comparison shows that people are not asking for unrealistic or impossible levels of performance if they demand an end to careless underprocessing, in order to reduce radiation overdosing by a large amount. When facilities make the effort to do processing right, there is proof that it happens.
3g. A Realistic First Step: Cutting Careless Overdoses in Half
The evidence in Part 3, above, explains some comments by UNSCEAR early in its presentation: "From a radiation protection point of view, doses should be maintained as low as reasonably achievable. This means that exposures above clinically acceptable minimum doses, must be avoided. There is much potential for reducing the risks associated with medical radiation exposures for diagnostic or therapeutic purposes" (1993, p.227/34). And:
"Although the doses from diagnostic x-ray examinations are generally relatively low, the magnitude of the practice makes for a significant radiological impact" (1993, p.228/40). And later:
"A United Kingdom report (NRPB 1990) gives detailed recommendations for reducing patient doses ... It estimates that about half of the current collective effective dose to patients from x-rays could be avoided. This conclusion is drawn in spite of the relatively low frequency of examinations (about twice as many examinations per caput are performed in France and the United States) ... Since it has been suggested that in the United Kingdom the collective effective dose from diagnostic x-rays could be halved (NRPB 1990), there is probably a potential for similar dose reductions in many countries" (UNSCEAR 1993, p.243/137+138).
Very gently, UNSCEAR is suggesting that the "significant radiological impact," from hundreds of millions of diagnostic x-ray exams occurring every year, could be cut in half by getting rid of careless overdosing. (And half could be just the first step.)
We are "allowed" to ask a question which UNSCEAR can not: If influential people know about this opportunity and do not use it, what does it say about a callous readiness to inflict upon people, at random, unnecessary cases of cancer --- including breast cancer?Part 4. WIXMEASE: A Potential Way to Stop Much Careless Overdosing
A double-dose of wishful thinking represents a big obstacle to solving the overdose problem.
o - The referring physicians who order the x-ray exams presently know virtually nothing about radiation, so they wish to believe that risks are just "hypothetical" and that they need not take any responsibility.
o - The patients hate to irritate their physicians, with whom they would like to have a warm relationship, so they too wish to believe that radiation risks are just "hypothetical" and that there is no need for them to challenge anyone.
These two sets of people comfortably reinforce each other, while the overdose problem persists.
4a. Getting Realistic? The Meaning of WIXMEASE
On the average, an individual's personal risk from a single x-ray exam is small, and is even smaller from the share of radiation which is the overdose. So, it is not realistic to think that individual physicians or individual patients are going to look beyond their personal stakes and to take responsibility for the aggregate impact from millions and millions of overdoses, occurring year after year --- an impact particularly dangerous for patients who have inherited an extra vulnerability to ionizing radiation (see p.181; also Part 5, below).
Then does anyone care? The women who have committed themselves to preventing as many cases of breast cancer as possible, must surely care about the radiation-induced cases which result from careless overdosing.
It may be in their power to establish a practical service which would solve the careless overdosing problem while not disturbing the mutual comfort of the referring physicians and their patients. What about a Women's Independent X-ray Measurement Service? WIXMEASE.
4b. The Effect of Information
The first step in any serious effort to eliminate careless overdosing would seem to be an independent measurement system to find out where the overdoses occur. A lot could be accomplished just by using TLDs, which can measure entrance dose during an examination without interfering with the x-ray image (see p.298).
For years, a Monitoring-by-Mail Service has existed --- but not for the public --- at the University of Wisconsin's Medical Physics Lab in Madison, Wisconsin (Telephone: 608-262-6320). The Mail Service supplies TLDs to physicians and others who irradiate people, receives the TLDs back by mail, and evaluates the dose on each TLD.
Women of course are perfectly capable of developing their own expertise, or of hiring expertise, to run a similar service --- with one big difference: The TLDs might belong to the patients, and the dose information would become part of a growing database, openly accessible to other patients, referring physicians, and x-ray offices. Finally, it would become possible, on a current basis, to avoid places which typically give higher doses (or more repeats) than other places. Careless places would have either to "shape up," or to fail.
If information on comparative doses were readily available (for instance, on the Internet), what physician would refer patients to a high-dose facility, or to one which declined to participate --- and what patient would go? After a while, insurance systems might refuse reimbursement to non-participants in an independent, trustworthy measurement service. WIXMEASE would not need to remain the only service, if others decided to provide similar, accessible services. The more competition, the more protection against carelessness and corruption at any single service.
4c. The Effect of Independent Information
We do not underestimate the problems of getting a pilot project funded and successfully underway in one or more metropolitan areas. However, we certainly do not underestimate the talent and tenacity of the women who, in the past few years, collected 2.6 million signatures from U.S. citizens demanding a more intense national effort to reduce the incidence of breast cancer, who managed to increase the federal budget for breast-cancer research by a great deal, and who managed to establish a special tax in California to do something new about preventing breast cancer (Chapter 43, Part 3).
Nor do we underestimate the probable resistance from some physicians who will be fearful of patients "having information which they can't understand."
Today, patients who ask x-ray offices about doses often receive answers --- and those answers may sometimes be pure fiction, looked up in a manual of what the dose should be. Isolated answers, even if true, do nothing to eliminate the undeniable overdose problem. By contrast, independent, credible, systematic, current sources of information, based on actual measured doses, would do a very great deal to eliminate careless overdosing.Part 5. Inappropriate Time in History to Assume the Problem Is "Past"
It seems to us a particularly inappropriate time in history to assume that the causal role of medical radiation in the cancer problem is "past" and now small. We put the emphasis on history for the following reasons:
o - The evidence that there is no safe dose-level of radiation has only recently been acknowledged as decisive (Chapter 45).
o - Very recent technical advances in molecular biology are confirming the multi-step genetic model of carcinogenesis --- with its implication that radiation and non-radiation carcinogens probably make each other worse (see Index: Co-action).
o - Very recent work is expanding our knowledge about rather large subsets of the population who have inherited a defective system for repairing radiation-induced genetic damage. For instance, Scott reports that sensitivity to radiation-induced chromosome damage has already been shown in more than 15 cancer-prone conditions (Scott 1994-a, Scott 1994-b; Sanford 1990; see also Savitsky 1995, p.1749, and Nowak 1995, p.1701).
o - The rapidly expanding world population, aspiring to "Level One" health care, means that a huge increase in person-rads of collective radiation dose is coming. And due to poverty, the temptation to use inexpensive fluoroscopy is strong. UNSCEAR 1993 mentions Tunisia, where over 50 percent of the radiologic equipment is fluoroscopic --- and is said to be used more often to please patients than to obtain diagnostic information (p.243/139). In China, allegedly "98 percent of all x-ray diagnosis is done with fluoroscopy" (Caufield 1989, p.225, citing a 1987 interview with Dr. Fred Mettler). In Belarus and Russia (where the population is not growing), we have been told that fluoroscopy is used "for everything" because film and film processing is not affordable.
o - The longer lifespan in the affluent countries means a shift in their populations' age-distribution toward older ages --- when more (not less) diagnostic and interventional radiology is used.
o - The number of breast cancers treated by surgery plus adjuvant radiation is growing, and this means a growing number of women at risk for a radiation-induced cancer in the other breast. During radiation therapy, the medial (mid-body) side of the other breast receives hundreds of rads of exposure from scattered radiation, for "most patients" (Muller-Runkel 1990, p.874).
o - The common diagnostic x-ray examinations of "the past" are still in use --- and many of them are breast-irradiators (Part 2d, above). In addition, new examinations (CT Scans, for example, and diagnostic nuclear medicine) have been added to the breast-irradiating scene, and their use is growing (Part 2b).
o - An enormous expansion of mammography has occurred and is very likely to continue, and this screening technique means repeated irradiation of many healthy breasts (Part 2b).
o - There is an undeniable overdose problem today in diagnostic and interventional radiology (Part 3), and even small overdoses and small risks become significant, when multiplied by hundreds of millions of occurrences year after year. For people born radio-sensitive, careless radiation overdosing, during a lifetime of medical care, is no small matter.
o - UNSCEAR 1993 estimates that the aggregate annual radiation dose from diagnostic radiation could be cut in half, without interfering with appropriate usage and needed medical information (Part 3g).
This list is a reality-check on the hasty but common assumption that medical radiation is a problem of "the past" with respect to causation of future breast-cancers (and other cancers). Still, no one should be surprised by the attitude of the medical profession. Recently (but in a different context: Lancet 1993, p.344), the editors of The Lancet remarked on "the extraordinary capacity of the profession for self-delusion."
------------------------------------------------------------------------------- | | Entrance-Dose | | Area | Procedure Reduction- Reference | | | Factor | |-----------------------------------------------------------------------------| | All Types | Elimination of medically 1.2 Cohen 1985. | | | unnecessary procedures | | | Introduction of Quality | | | Assurance programme (general) 2* Cohen 1985. | |-----------------------------------------------------------------------------| |Radiography | Decrease in rejected films through 1.1 Gallini 1985. | | | Quality Assurance programme Properzio 1985. | | | | | | Increase of peak kilovoltage 1.5 Wiatrowski 1983. | | | | | | Beam collimation 1 to 3 Johnson 1986. | | | Morris 1984. | | | | | | Use of rare-earth screens 2 to 4 Kuhn 1985. | | | Newlin 1978. | | | Segal 1982. | | | Wagner 1976. | | | | | | Increase of filtration 1.7 Kuhn 1985. | | | Montanara 1986. | | | Wiatrowski 1983. | | | | | | Rare-earth filtration 2 to 4 Tyndall 1987. | | | | | | Change from photofluorography 4 to 10 Jankowski 1984. | | | to chest radiography Mustafa 1985. | | | Neamiro 1983. | | | Use of carbon fibre materials 2.0 Huda 1984. | | | | | | Replacement of CaW04 screens with 4.0 Kuhn 1985. | | | spot film technique | | | | | | Entrance exposure guidelines 1.5 Laws 1980. | | | | | | Gonadal shielding 2 to 10 ** Poretti 1985. | |-----------------------------------------------------------------------------| | Pelvimetry | Use of CT topogram 5 to 10 Stanton 1983. | |-----------------------------------------------------------------------------| |Fluoroscopy | Acoustic signal related to dose rate 1.3 Anderson 1985. | | | | | | Use of 105 mm camera 4 to 5 Rowley 1987. | | | | | | Radiologist technique 2 to 10 Rowley 1987. | | | | | | Variable aperture iris on TV camera 3.0 Leibovic 1983. | | | | | | Change from chest fluoroscopy to 20.0 Sun 1985. | | | radiography | | | | | | High and low dose switching 1.5 Leibovic 1983. | |-----------------------------------------------------------------------------| | Digital | Decrease in contrast resolution 2 to 3 Rimkus 1984. | |radiography | | | | Use of pulsed system 2 Rimkus 1984. | |-----------------------------------------------------------------------------| | Computed | Gantry angulation to exclude eye 2 to 4 *** Isherwood 1978.| |tomography, | from primary beam | | head | | |-----------------------------------------------------------------------------| |Mammography | Intensifying screens 2 to 5 NCRP 1986. | | | Shrivastava 1980.| | | | | | Optimal compression 1.3 - 1.5 NCRP 1986. | | | | | | Filtration 3 Hammerstein 1979.| | | | |-----------------------------------------------------------------------------| | * The role of proper training in radiation protection is extremely | | important. Dose reduction-factors in this regard may be large; | | however, they are difficult to quantify. | | ** Factor for gonads. | |*** Factor for eyes. | -------------------------------------------------------------------------------