Part 1. Chiropractic Spine Examinations: How Many ?
In the most recent reprinting (June 15, 1994), NCRP Report No. 100 (p. 16) cites the American Chiropractic Association indicating that, in 1982, chiropractors performed about 10 million x-ray examinations of the spine. And at page 12, NCRP 100 cites the American College of Radiology Manpower Survey (ACR 1982) as indicating that, in 1980, chiropractors performed an estimated 10 million medical diagnostic x-ray examinations, this number being about 5.5% of all the 180 million diagnostic x-ray examinations for the year.
Priscilla Laws, in X-rays: More Harm Than Good ? (1977) stated at page 43: "Chiropractors are popular in both Canada and the United States, and a 1971 survey of the Journal of Clinical Chiropractic indicates that more than 10 million x-ray examinations were being conducted by United States and Canadian chiropractors annually. At least two million of those were the type which irradiates the body from the skull to the thigh, including the thyroid, bone marrow, and reproductive organs." This is the examination known as the "Full-Spine Exam."
All of these reports are quite consistent with each other. For total spine exams by chiropractors in 1980, we will use the figure 10 million per year, of which 2 million were Full-Spine Exams (males and females combined).
We have a detailed reference (Bhatnagar and co-workers 1981) on the dosimetry for the Full-Spine Exam.
From that source, the mean dose to breast tissue = 465 milli-rads, including dose to breast from one antero-posterior (AP) exposure and one lateral (LAT) exposure. (These doses, say the authors, are for examinations as performed in one chiropractor's office in the Pittsburgh area.) This publication appeared in print in 1981, but was presented in 1980. We have many reasons to expect that doses in the early period (1920-1960) were higher, not lower than in later periods.
o - Item 1: For conservatism, we shall assume that the breast-dose per Full-Spine Exam was 0.465 rad during the 1920-1960 period.
o - Item 2: We shall reduce the 2,000,000 Full-Spine Examinations for the 1920 - 1960 period in proportion to population. The average female population for 1920-1960 we have determined is 69,037,400, for all ages combined. And for 1980 (Statistical Abstract of United States) the female population is 116,493,000. Therefore, our adjustment factor for population size is (69,037,400 / 116,493,000), or 0.593. And we must omit males.
We reduce the 2,000,000 Full-Spine Examinations by a factor of two for female population, which gives 1,000,000 exams. Then, reducing this by the factor of 0.593, we end up with 593,000 Full-Spine Examinations by chiropracty in the 1920-1960 period, at an average breast-dose of 0.465 medical rads. This is a start on the problem of the total dose from various spine examinations. Having taken care of Full-Spine Exams separately, we now consider the remaining 8,000,000 spine examinations annually. We must multiply this number by (0.5) to get to the value for females only, and by 0.593 to get to 1920-1960 period. So we have (8 million) x (0.5) x (0.593), or 2,370,000 spine examinations additional to the Full-Spine Examinations.
Col. A Col. B Col. C Col. D Col. E Col. F Col. G Col. H Beam Breast Raising Lumbar Projections Quality Entrance Average Rads per Factor Breast Spine Taken HVL, Exposure No. Films Entrance for Beam Rads per mm, Al. Roentgens per Exam Roentgen Quality Exam AP 2.37 0.88 1.03 0.693 1.03 0.650 LAT 2.58 3.20 1.33 0.183 1.25 0.973 OBL-PA 2.51 1.11 0.46 0.110 1.20 0.067 Total Breast-Dose in rads for complete exam -----> 1.690 Beam Breast Raising Thoracic Projections Quality Entrance Average Rads per Factor Breast Spine Taken HVL, Exposure No. Films Entrance for Beam Rads per mm, Al. Roentgens per Exam Roentgen Quality Exam AP 2.37 0.66 1.07 0.693 1.03 0.51 LAT 2.42 1.46 0.93 0.183 1.11 0.28 OBL-PA 2.42 0.76 0.12 0.110 1.12 0.01 Total Breast-Dose in rads per complete exam -----> 0.79
Notes: Gofman/O'Connor 1985 provides the factor by which rad doses must be raised when the Half-Value Layer deviates from 2.3 mm Al (Table D). The rads per Entrance Roentgen are also provided there (Table C).
Entrance doses for such examinations are provided in Table 3.19 from NCRP 100.
The NCRP and Gofman projections and entrance doses are in perfect agreement.
Final Breast Rads per Exam are in Col. H, which = (Col.D) x (Col.E) x (Col.F) x (Col.G).
The lumbar spine films are by far the most common spine films aside from the Full-Spine Examination. Using the data from Table 3.7 of NCRP 100, we estimate the lumbar plus thoracic spine exams together will constitute 80% of of the spine films other than the Full-Spine Examination. Therefore, we shall reduce the 2,370,000 spine exams to 80% of that value, or 1,896,000 exams divided between lumbar plus thoracic spine examinations.
In the 1964 period, thoracic spine exams constituted 0.17 of the total (thoracic + lumbar) exams, and lumbar exams consituted 0.83 of that total.
In the period up through 1963, the "wasted radiation," namely the area exposed relative to the area needed for the x-ray, was about 3.2-fold (NCRP 100 concurs). See also Chapter 23. So the lumbar films can be considered to have had the breasts fully in the field, since there was already high exposure to breasts for this exam even without the wasted radiation. (See `Lumbar Spine,' p.126 in Gofman / O'Connor 1985.)
Next, we can estimate an average breast-dose for thoracic and lumbar spine exams by combining these two exams in their relative proportions (doses taken from the box).
Average Dose = (0.83 x 1.69) + (0.17 x 0.79) = 1.54 medical rads.
This dose applies for 1,896,000 examinations, which can be handled (mathematically) like 1,896,000 persons.
o - Item 3: Total accumulation of person-rads to the breasts in the United States Population:
Full-Spine: (593,000 persons) x (0.465 rads) = 275,745 person-rads.
Other,Spine: (1,896,000 persons) x (1.54 rads) = 2,919,840 person-rads.
Total person-rads, all spine exams = 3,195,585 person-rads.
o - Item 4: These person-rads will be distributed into all females between 15 and 64 years of age, a total of 50 age groups. We do not have the precise age distribution of dose, so we shall assume each age group gets 1/50 of the total, which is 3,195,585/50, or 63,912 person-rads per age-year category, rounded off.
o - Item 5: We must next determine the average population dose in rads. Since we have to deal with 50 different age-groups, we shall demonstrate here how the estimate is made, and in the Master Table (Col. R), the actual calculations of dose will be presented for each of the fifty age-years.
Let us take the national population of women in the 15th year age bracket. That number from Master Table, Column A, is 888,277 women.
If we distribute 63,910 person-rads into 888,277 women, the average dose per woman is (63,912 women-rads) / (888,277 women), or 0.072 rads.
This value will not differ very much from age-group to age-group since the only basis for difference is the decline in population-number with increase in age.
o - Item 6: There is no reason to assume this practice was not carried out throughout the 1920 to 1960 period. Indeed, it was still going strong in the 1980's.
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o - Safety Claims about Low-Dose Radiation:
A Warning from the National Cancer Institute (NCI) in 1990
This book (Preventing Breast Cancer) states there is no safe dose of ionizing radiation with respect to induction of breast-cancer (or other cancers).
Various women have recounted to us that they have been advised that cancer is the result only of high doses of radiation, and that repair of DNA and chromosome eliminates all the injury at low radiation doses.
What does the National Cancer Institute tell the public? In its 1990 booklet (pp.9-10), it deals with the topic as follows, with question-and-answer:
"Are there safe levels for human exposure to carcinogens? In other words, are there threshold dosages below which we can be sure that no cancer will occur? " And:
"There is no adequate evidence that there is a safe level of exposure for any carcinogen. As far as we know, the frequency of tumor formation goes down as the dosage goes down, but the risk of carcinogenesis may not disappear until the dosage reaches zero. Although high doses are often used in the [animal] tests, we must not assume that only high doses cause cancer. On the contrary, we must assume that low doses will also cause cancer, but at lower rates." And:
"Human cancers have occurred following very low level exposure. Asbestos brought home on the clothing of asbestos workers, for example, has caused fatal cancers in members of the workers' families."
Source: National Cancer Institute (USA), "Everything Doesn't Cause Cancer," 12-page booklet, March 1990 (NIH Publication 90-2039).
Note: For induction of cancer by ionizing radiation, there is mainstream evidence (from humans, not from test-animals) disproving any safe dose or dose-rate. See Gofman 1990, Chapters 18-21, 32, 33. In addition, human studies (like the A-Bomb Study) provide evidence of a dose-response --- that is, the frequency of radiation-induced cancer goes down when dose goes-down (and goes up when dose goes up). A dose-response is important in helping to exclude non-radiation explanations.