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CHAPTER 40
Conversion Factors: The Basis of
Column "V"
Part 1. Introduction
By the term "conversion-factor" in this book, we mean any
formula which estimates how many radiation-induced
breast-cancers result from a specified amount of
population-exposure --- for example, from 10,000 person-rads of
exposure. In this book, the term person-rads refers to
breast-rads.
The conversion-factors developed in this chapter differ slightly
from the conversion-factors published in our preliminary work
for this book. We continue to study the problem of
conversion-factors; many other analysts continue to study the
problem, too; and relevant new evidence continues to
accumulate. So we expect the conversion-factors to keep
improving in the future. Meanwhile, this chapter presents one
of several ways to arrive at conversion-factors, in view of what
is presently known, and what is presently unknowable.
Part 2 of this chapter begins where
Chapter 15 of
our 1990 book
ended. Otherwise, we would have to repeat most of the earlier
book. Readers who are not familiar with the previous book can,
nonetheless, follow what we do here with the "starting point"
from the earlier work (Gofman 1990).
Part 2. Step-by-Step Development of Our Conversion Factors
Our starting point for developing conversion-factors is the
study of atomic-bomb survivors. Why don't we use evidence based
in the United States, since this book focuses on the
breast-cancer problem in the USA? The answer is simple: Only
the A-Bomb Study provides observations for women irradiated at
every age, and then followed-up for decades. No comparable
study exists for American women.
We have analyzed both the 1950-1982 and the 1950-1985 follow-up
evidence from Japan on radiation-induced cancer mortality. The
more recent data are not yet available to us from RERF (as of
January 1995). Here, we will use the 1950-1982 data, because
readers can refer to Gofman
1990 to check exactly how we handled those data in reaching
our starting point for this chapter.
We begin by presenting a series of six boxes, which are
subsequently explained in the text. [For
accessibility, we also include each box at the beginning
of its own section here on the web version
--ratitor]
BOX 1, "Starting Point." All cancer-types, excluding leukemia.
A B C D
Age when Cancer-deaths Cancer-deaths Difference
exposed per 10,000 per 10,000 per 10,000
(years) initial females initial females initial females
as of 1982, in as of 1982, in as of 1982
high-dose group low-dose group (B minus C)
0-9 150.94 55.41 95.53
10-19 295.23 153.32 141.91
20-34 637.48 451.57 185.91
35-49 1318.68 1077.37 241.31
50+ 1246.33 1040.42 205.91
BOX 2, Lifetime Factors. All cancer-types, excluding leukemia.
A D E F
Age when Age when Difference Lifetime Lifetime excess
exposed exposed per 10,000 factor of cancer-deaths
(avg.) initial females increase per 10,000
as of 1982 initial females
(years) (years) (B minus C) (1059/Col C) (D times E)
0-9 4.1 95.53 19.11207 1825.776
10-19 14.9 141.91 6.90712 980.190
20-34 26.6 185.91 2.34515 435.987
35-49 41.7 241.31 none 241.31
50+ 58.9 205.91 none 205.91
BOX 3, Supra-Linearity Adjustment. All cancer-types, excluding leukemia.
A F G H
Age when Lifetime excess Supra- Lifetime excess
exposed cancer-deaths linearity cancer-deaths
(years) per 10,000 factor (per 10K females)
initial females adjusted for
(D times E) (see text) supra-linearity
(F times G)
0-9 1825.776 2.40 4381.863
10-19 980.190 2.24 2195.625
20-34 435.987 2.18 950.452
35-49 241.31 2.13 513.990
50+ 205.91 2.06 424.175
BOX 4, Division by Dose-Difference. All cancer-types, excluding leukemia.
A H I J K L
Age when Lifetime excess High-dose Low-dose Dose- Lifetime excess
exposed cancer-deaths group: group: difference cancer-deaths
(years) (per 10,000 Average Average in rads per 10K females
females) dose in dose in with avg dose
adjusted for rads rads (I minus J) = 1 A-bomb rad
supra-linearity (H / K)
0-9 4381.863 97.61 2.91 94.70 46.271
10-19 2195.625 89.20 2.50 86.70 25.324
20-34 950.452 87.38 2.63 84.75 11.215
35-49 513.990 80.87 2.76 78.11 6.580
50+ 424.175 71.73 2.51 69.22 6.128
BOX 5, Adjustment for Medical Rads. All cancer-types, excluding leukemia.
A L M N
Age when Lifetime excess Factor of Lifetime excess
exposed cancer-deaths increase for cancer-deaths
(years) per 10K females medical per 10K females
with avg dose rads with avg dose
= 1 A-bomb rad = 1 medical rad
(H / K) (L times M)
0-9 46.271 2 92.542
10-19 25.324 2 50.649
20-34 11.215 2 22.430
35-49 6.580 2 13.161
50+ 6.128 2 12.256
BOX 6, Final Adjustments to Reach Conversion-Factors.
A N "O" P Q R S
Age when Lifetime excess Lifetime excess Incidence/ US/Japan "Lift-off" Conversion
exposed cancer-deaths breast-cancer mortality ratio of reduction factors
(years) per 10K females deaths per 10K ratio for breast- factor for Master
with avg dose fem with avg dose breast- cancer Table.
= 1 medical rad = 1 medical rad cancer vulner- (see text) Described
(L times M) (see text) (see text) ability below *.
0-9 92.542 8.8315 3.704 5.67 0.50 92.74
10-19 50.649 4.8335 3.704 5.67 0.75 76.13
20-34 - 22.430 2.1405 3.704 5.67 1 44.95
35-49 13.161 1.2560 3.704 5.67 1 26.38
50+ 12.256 1.1696 3.704 5.67 1 24.56
* Each conversion factor
is the estimated number of radiation-induced excess
breast-cancer cases (lifetime incidence) per 10,000 females
(USA) from an average breast-dose of one medical rad. Each
entry in Column S is the product of Columns "O" x P x Q x R.
BOX 1, "Starting Point." All cancer-types, excluding leukemia.
A B C D
Age when Cancer-deaths Cancer-deaths Difference
exposed per 10,000 per 10,000 per 10,000
(years) initial females initial females initial females
as of 1982, in as of 1982, in as of 1982
high-dose group low-dose group (B minus C)
0-9 150.94 55.41 95.53
10-19 295.23 153.32 141.91
20-34 637.48 451.57 185.91
35-49 1318.68 1077.37 241.31
50+ 1246.33 1040.42 205.91
o - BOX 1, Starting Point
In Box 1 are the
findings for cancer mortality for all types of
cancer (leukemia excluded) in the female population, divided
into low-dose and high-dose groups for five separate age-groups
(age in 1945, at the time of the bombings). The observed
differences between high-dose and low-dose groups (Column D, Box
1) are the radiation-induced cancer-deaths.
The boxed data come from Tables
15-G,
15-H,
15-I,
15-J, and
15-K
of Gofman 1990. We
are using the entries from those tables in
the T65DR dosimetry. Those very same tables show that the
results are negligibly different when the revised DS86 dosimetry
is used properly. By "properly," we mean that the cohorts
remain constant (no shuffling of cases) while receiving a
revised estimate of average dose from the DS86 system.
Our protest against the retroactive shuffling of cohorts, and
against the constant retroactive alteration of the DS86 database,
is fully presented in Gofman
1990 (especially Chapters 5 and
6). In our opinion, use of the unstable
DS86 database (which already has many versions) is scientifically
acceptable only as part of a "constant-cohort, dual-dosimetry"
analysis in which the T65DR system remains the stable anchor for
the follow-up studies.
BOX 2, Lifetime Factors. All cancer-types, excluding leukemia.
A D E F
Age when Age when Difference Lifetime Lifetime excess
exposed exposed per 10,000 factor of cancer-deaths
(avg.) initial females increase per 10,000
as of 1982 initial females
(years) (years) (B minus C) (1059/Col C) (D times E)
0-9 4.1 95.53 19.11207 1825.776
10-19 14.9 141.91 6.90712 980.190
20-34 26.6 185.91 2.34515 435.987
35-49 41.7 241.31 none 241.31
50+ 58.9 205.91 none 205.91
o - BOX 2, Adjustment for Lifetime Follow-Up
The values in Box 1 cover only the
period through 1982. We (and others) have to estimate
what the observations may be when all
the initial participants have been followed for their full
lifespans. In 1945, the average age of the 50+ age-group was
58.9 years for females, and average age was 41.7 years for the
age-group 35-49 years (Gofman
1990, Table 26-G). In
1982, both of these age-groups have essentially told their lifetime
"story," so we can use those results without adjustment. But we
must make estimates for the other three age-groups.
How? Tables 15-G
through 15-K of
Gofman 1990 show that the
whole-body dose in the low-dose groups was very similar in all
five age-bands (range = 2.50 rems to 2.91 rems). So we will use
the approximation that the low-dose women in the three youngest
age-groups will "behave" like the two oldest age-groups, with
respect to lifetime rate of cancer mortality. When we
average the lifetime rates of the two oldest age-groups, we
obtain 1,059 cancer deaths per 10,000 initial women.
For the age-group 0-9 years, the value 1,059 represents a
19.112-fold multiplication of the 55.41 rate observed in 1982
(Box 1, Column C). For the age-group
10-19 years, 1,059 represents a 6.907-fold multiplication of
the 153.32 rate observed in 1982. And for the age-group
20-34 years, 1,059 represents a 2.345-fold multiplication of
the 451.57 rate observed in 1982. These "lifetime factors"
are shown in Box 2, Column E. (As usual, we retain all the
digits without endowing them with the formal status of
"significant figures.")
And what about the lifetime difference between the high-dose and
low-dose groups --- the lifetime radiation-induced excess for
the three youngest age-groups? For now, we temporarily use the
assumption that the difference will also increase by the same
"lifetime factors." Later, in Box 6, we make
downward adjustments for the two youngest age-groups. Meanwhile,
Box 2 applies the "lifetime factors" to
obtain the estimated lifetime excess of cancer-deaths (all
sites) per 10,000 initial females (Column F).
BOX 3, Supra-Linearity Adjustment. All cancer-types, excluding leukemia.
A F G H
Age when Lifetime excess Supra- Lifetime excess
exposed cancer-deaths linearity cancer-deaths
(years) per 10,000 factor (per 10K females)
initial females adjusted for
(D times E) (see text) supra-linearity
(F times G)
0-9 1825.776 2.40 4381.863
10-19 980.190 2.24 2195.625
20-34 435.987 2.18 950.452
35-49 241.31 2.13 513.990
50+ 205.91 2.06 424.175
o - BOX 3, Adjustment for Supra-Linear Dose-Response
The differences in Box 1 (Column D)
come from assuming a linear
dose-response. In reality, supra-linearity describes the
dose-response among the A-bomb survivors significantly better
than linearity, both in T65DR and DS86 constant-cohort analyses
Gofman 1990,
Chapters 14 and 29). The
shape of the dose-response
for 1950-1982, with all ages and both sexes combined, is
reproduced here from Figure
14-E of Gofman 1990. The
curve has the same shape in the DS86 dosimetry, properly handled
with "constant-cohorts."
We notice with interest that the excess relative risk
specifically for breast-cancer incidence also shows a
supra-linear shape in
Thompson 1994
(Figure 3, p.S26, which is a DS86 analysis not
anchored to T65DR cohorts).
If it were not for the bend of supra-linearity, the differences
between high-dose groups and low-dose groups would have been
approximately twice as high as the values presented in
Box 1, Column D. Indeed, we evaluated
how much higher for each female age-group separately in
Gofman 1990
(Chapter 15,
Part 6,
tabulation of factors). Now we must use those supra-linearity
factors to adjust the differences in Column F. This is done in
Box 3.
The supra-linearity adjustment explains why we refer to our
conversion-factors as "low-dose conversion-factors"
(Chapter 39, Part 1). The
supra-linearity adjustment bases the difference between high-dose
and low-dose groups on the steeper slope which
characterizes dose-response in the low-dose region
(approximately zero to five rads). Readers have seen
(initially in Chapter 8)
how we maintain the applicability of these
low-dose conversion-factors to exposures which occurred at
higher doses, too. We do it by adjusting doses downward,
whenever appropriate, by factors derived from the supra-linear
curve itself.
BOX 4, Division by Dose-Difference. All cancer-types, excluding leukemia.
A H I J K L
Age when Lifetime excess High-dose Low-dose Dose- Lifetime excess
exposed cancer-deaths group: group: difference cancer-deaths
(years) (per 10,000 Average Average in rads per 10K females
females) dose in dose in with avg dose
adjusted for rads rads (I minus J) = 1 A-bomb rad
supra-linearity (H / K)
0-9 4381.863 97.61 2.91 94.70 46.271
10-19 2195.625 89.20 2.50 86.70 25.324
20-34 950.452 87.38 2.63 84.75 11.215
35-49 513.990 80.87 2.76 78.11 6.580
50+ 424.175 71.73 2.51 69.22 6.128
o - BOX 4, Division by Dose-Difference
So far, we have not considered the difference in dose which
produced the difference in cancer-rates. In order to obtain
the lifetime excess per rad, we use Box 4
to divide the values in Column H by the dose-differences, for
which the data are provided by age-group in
Gofman 1990,
Tables 15-G
through 15-K. This
provides lifetime excess cancer-deaths per 10,000 females,
from an average dose of one A-bomb rad.
BOX 5, Adjustment for Medical Rads. All cancer-types, excluding leukemia.
A L M N
Age when Lifetime excess Factor of Lifetime excess
exposed cancer-deaths increase for cancer-deaths
(years) per 10K females medical per 10K females
with avg dose rads with avg dose
= 1 A-bomb rad = 1 medical rad
(H / K) (L times M)
0-9 46.271 2 92.542
10-19 25.324 2 50.649
20-34 11.215 2 22.430
35-49 6.580 2 13.161
50+ 6.128 2 12.256
o - BOX 5, Adjustment for Medical Rads
It is widely agreed that the carcinogenic potency of high-energy
gamma-rays is less than the potency of lower-energy x-rays, as
mentioned in Chapter 3,
Part 1. The
"ballpark" estimate is that medical x-rays are about two-fold
more carcinogenic, per rad, than high-energy gamma-rays (references
in Gofman 1990,
Chapter 13,
Part 4). Thus,
if the Hiroshima-Nagasaki exposure had been
to x-rays instead of A-bomb gamma-rays, the number of excess
cancers per 10,000 women, from an average dose of one medical
rad, would have been about twice as great. Box 5 converts
Column L from A-bomb rads to medical rads.
BOX 6, Final Adjustments to Reach Conversion-Factors.
A N "O" P Q R S
Age when Lifetime excess Lifetime excess Incidence/ US/Japan "Lift-off" Conversion
exposed cancer-deaths breast-cancer mortality ratio of reduction factors
(years) per 10K females deaths per 10K ratio for breast- factor for Master
with avg dose fem with avg dose breast- cancer Table.
= 1 medical rad = 1 medical rad cancer vulner- (see text) Described
(L times M) (see text) (see text) ability below *.
0-9 92.542 8.8315 3.704 5.67 0.50 92.74
10-19 50.649 4.8335 3.704 5.67 0.75 76.13
20-34 - 22.430 2.1405 3.704 5.67 1 44.95
35-49 13.161 1.2560 3.704 5.67 1 26.38
50+ 12.256 1.1696 3.704 5.67 1 24.56
* Each conversion factor
is the estimated number of radiation-induced excess
breast-cancer cases (lifetime incidence) per 10,000 females
(USA) from an average breast-dose of one medical rad. Each
entry in Column S is the product of Columns "O" x P x Q x R.
Part 3. Explanation of BOX 6: Transition to Breast-Cancer Incidence, USA
Every step to reach the entries in Column N has an anchor in
various real-world observations. And what we have, so far, are
the numbers of radiation-induced cancer-deaths (all sites) per
10,000 females, from an average dose of one medical rad, for
five different age-groups. What we want are the estimated
numbers of radiation-induced breast-cancer cases per 10,000
females, per medical rad, for each age-group. So, we continue
to look for anchors in real-world observations to make the next
transitions.
o - Transition to Breast-Cancer - Column "O"
We know the relationship of the all-cancer death-rate to the
breast-cancer death-rate in Japanese females for 1964-1965
(American Cancer Society 1970, pp.22-23). These rates for the
entire country are barely influenced by the atomic bombings.
The years 1964-1965 are chosen by us because they are
approximately the midpoint of the 1950-1982 follow-up study from
which we obtain our knowledge of radiation-induced rates. The
all-cancer deaths per 100,000 Japanese females were 94.7 deaths
per year. The breast-cancer deaths per 100,000 Japanese women
were 3.8 deaths per year. The fraction of cancer-deaths which
came from breast-cancer was 3.8 / 94.7, or 0.040127 --- four
percent. If all cancers were equally radiation-inducible, then
we could assume that approximately four percent of the
radiation-induced excess cancer-deaths in Column N would be from
breast-cancer. But it is not so simple.
We also have the observation that breast-cancer is more
inducible by radiation than other cancers. This observation
comes from the 1994 Thompson Study of cancer incidence in the
A-bomb survivors, 1958-1987. Although the Thompson Study is a
DS86 analysis which is not anchored to the T65DR cohorts, it is
unlikely that this shortcoming distorts the ratio of relevance
here The ratio of observed Excess Relative Risk (per sievert)
for breast-cancer, over the observed Excess Relative Risk (per
sievert) for cancers at all sites --- including breast-cancer.
That ratio is 1.59 / 0.63, or 2.524 (from
Thomspon 1994, pages
S26, S49, S61). Breast-cancer has by far the highest Excess
Relative Risk of any cancer reported at page S26.
In the ratio above, the denominator of 0.63 for all sites
includes breast-cancer. The all-site value would be lower than
0.63 if it were not elevated by breast-cancer. This means that
the radiation-inducibility of breast-cancer must be somewhat
more than 2.524-fold higher than the radiation-inducibility of
non-breast-cancers. However, the available data do not
allow us to adjust the ratio for females alone.
(a) So, we use the 2.524-factor without adjustment, as a
reasonable "first approximation" for the relative inducibility
of breast-cancer versus non-breast-cancer by ionizing
radiation.
(b) Also, we use the vital statistics from above to estimate
the ratio of cancer mortality from breast-cancer to cancer
mortality from non-breast-sites. The breast-rate (per 100,000
women per year) is 3.8 when all-site-rate is 94.7, so the
non-breast-rate is (94.7 minus 3.8), or 90.9. So the ratio of
breast-cancer mortality to non-breast-cancer mortality is (3.8 /
90.9), or 0.041804.
Then, for each radiation-induced entry in Column
N, what is the estimated number from breast-cancer?
The first entry, 92.542 excess cancer-deaths = (the
radiation-induced number from non-breast sites) + (the
radiation-induced number from the breast).
Let n = the number of non-breast cancer-deaths produced per
10,000 women from an average dose of one medical rad.
The number of breast-cancer deaths produced per 10,000 per rad
will be (n) x (0.041804, which is the breast to non-breast
ratio) x (2.524, which is the radiation-inducibility factor).
The product = 0.1055n = breast-cancer cases. This term for
breast-cancer cases will be used for all five age-groups.
Hence, for the age-years 0-9, we treat the all-site value of
92.542 cases (from Column N) as follows:
92.542 radiation-induced cancers = non-breast cases + breast
cases = (n) + (0.1055n) = 1.1055n. Therefore:
n = 83.71 = non-breast cases. And:
Breast cases = 0.1055n = 8.83 radiation-induced cases.
Using the same procedure, we obtain values in
Column "O" for all five age-groups.
o - Transition to Incidence - Column P
How shall we convert the estimates for radiation-induced
breast-cancer mortality to incidence? Again, we have real-world
observations from the study of A-bomb survivors. For the
1958-1987 period, the reported ratio of breast-cancer mortality
to incidence is 0.27 (Mabuchi
1994, Table 4, page S10). This is, of course, an incidence
to mortality ratio of (1 / 0.27), or 3.704. We do not think this
ratio is likely to be distorted by a DS86 analysis, even though
the Mabuchi analysis is not anchored to the constant T65DR
cohorts. (Our comments about T65DR and DS86 occur with
Box 1, above.) Mabuchi et al also
report that the mortality/incidence relationship for solid
tumors is observed to be very nearly the same for exposed and
non-exposed participants in the study
(Mabuchi 1994, Table 5,
p.S10).
We will use the assumption that if radiation-induced
cancer-mortality (at any site) goes up by 5 cases (for example),
the radiation-induced incidence at the same site goes up by (5
cases) times (the ratio of incidence over mortality). Thus, to
convert Column "O" to breast-cancer
incidence, we multiply its entries by 3.704 (displayed in
Column P).
o - Transition to the USA - Column Q
For reasons which are not yet understood --- and which badly
need to be understood --- the rates of specific cancers often
vary enormously from country to country. In Japan, the
so-called spontaneous rate of breast-cancer is very much lower
than in the United States. We will evaluate the reported
US/Japan rates for 1964-1965, approximately the midpoint of the
A-Bomb Study follow-up. For the USA, breast-cancer deaths per
100,000 females per year were 21.55; for Japan, they were 3.80
(from American Cancer Society 1970, p.23). The vulnerability to
breast-cancer for women in the United States was 5.67-fold
greater than for women in Japan. In view of this difference, we
are making the assumption, tentatively, that the number of
radiation-induced cases per 10,000 females, from an average dose
of one medical rad, is about 5.67-fold higher in the USA than
among A-bomb survivors. So, 5.67 is entered into
Column Q as the US/Japan ratio.
Up until this point, our conversion-factors are based on the
number of excess cases per rad derived from the Japanese
experience. Use of the ratio of 5.67 in Column Q
acknowledges the real-world difference in "background" rates of
breast-cancer in the USA versus Japan. Use of this factor with our
method is equivalent to saying that the percent increase in
the background rate, per rad of radiation exposure --- the Excess
Relative Risk --- is approximately the same from one population to
another, regardless of differences in their background
rates. If the percent increase per rad is the same in the USA and
Japan, then one rad of breast-exposure induces more cases of
breast-cancer in the USA than in Japan.
The concept that ionizing radiation induces different numbers of
cancers per rad, in one country versus another, is consistent
with the concepts that --- within a single country and a single
study, such as the A-Bomb Study --- the lifetime number of
cancers induced per rad differs by site (for example, breast
versus bone) and differs by age at the time of exposure. In
other words The number of radiation-induced cases per rad is
not fixed by the number of genetic lesions induced. The number
of radiation-induced cancers per rad differs with the
circumstances.
Circumstances can differ within a population, and also from one
country to another. If ionizing radiation acts in concert with
some other factors (internal or external), present in the USA
but less present in Japan, the interaction could well cause a
six-fold disparity in the vulnerability for breast-cancer per
medical rad. We do not suggest that a rad in the USA induces
six times as many genetic lesions as it causes in Japan. We
(and others) suggest only that the impact of carcinogenic
lesions is affected by co-factors --- and vice versa. Whatever
combined factors cause the breast-cancer mortality rate in the
mid-1960s to be 5.67 times higher in the USA than in Japan,
these combined factors also cause radiation-induced genetic
lesions from medical irradiation to have a greater effect in the
USA than in Japan.
At this time, we think the 5.67 ratio of background
breast-cancer mortality-rates (USA / Japan, in the mid-1960s) is
the most reasonable approximation to use in our
conversion-factors. As additional evidence develops, it may
point to other ways to handle country-to-country "transport" of
observations. Meanwhile, we keep an open mind toward a variety
of old and new hypotheses about the actual process of radiation
carcinogenesis, including interaction between radiation and
other factors.
A Closer Look at Recent Cancer-Rates, USA vs. Japan
It is interesting to compare cancer rates between the USA and
Japan. By no means is the far higher U.S. rate for breast-cancer
a general phenomenon, as shown by the female and male tabulations
below. For stomach cancer, the Japanese rate is far higher than
that for the United States. And overall, the Japan cancer rates
are not very different from those in the United States (see "All"
in the tabulations).
All data are death rates, 1988-1991 per 100,000 population, age
adjusted to the WHO world standard population. (From
ACS 1994, at page 28.)
Cancer Japan U.S. Ratio Cancer Japan U.S. Ratio
Site Females Females U.S/Japan Site Males Males U.S/Japan
Breast 6.3 22.4 3.6 Prostate 3.8 16.8 4.4
Lung 8.0 24.7 3.1 Lung 30.1 57.1 1.9
Oral 0.6 1.3 2.2 Oral 2.3 3.7 1.6
All 76.7 110.6 1.4 Leukemia 4.3 6.3 1.5
Uterine Colon &
Cervix 1.8 2.6 1.4 Rectum 15.1 16.7 1.1
Leukemia 2.8 3.8 1.4 All 150.0 164.0 1.1
Colon & Stomach 34.9 5.2 0.1
Rectum 9.7 11.4 1.2
Uterine
Other 2.4 2.6 1.1
Stomach 15.5 2.3 0.1
Comparison of the Extremes
Cancer Sites Females Cancer Sites Males
Compared Compared
Breast USA/Japan 3.56 Prostate USA/Japan 4.42
Stomach USA/Japan 0.15 Stomach USA/Japan 0.15
Ratio: A Factor of 23.73 Ratio: A Factor of 29.47
Quite A Range of Relative Rates Quite A Range of Relative Rates
We do not think any single carcinogen, acting alone, explains
these vastly different relative rates.
A Suggestion That Will Not Compute
In the effort to deny the idea of a much greater
U.S. vulnerability to breast-cancer induction per medical rad
(Column Q), it has been suggested that the
observed relative rate in the mid-1960s of 5.67 is explained by
a possible difference in x-ray dose. If there was a
dose-difference (with higher annual average dose in the USA),
then it would help explain the relative rate in the
mid-1960s --- and it would have an additional implication
worth exploring. We will explore the suggestion, below, that a
dose-difference fully explains the 5.67 relative rate
for breast-cancer mortality.
The proposal is thus entertained, that female persons in the
United States had been getting much more x-radiation than female
persons in Japan and that this accounts for the relative rate of
5.67 in the mid-1960s. The relative rate of 5.67 means, of
course, an excess relative rate of (5.67 - 1.00), or 4.67. If
we were to blame the USA-Japan difference in rates totally upon
the difference in radiation dosage up to that time, we would be
saying that about 4.67 out of 5.67 breast-cancer deaths in the
United States at that time must have been x-radiation-induced
--- that is 82% of all breast-cancers were radiation-induced. So,
the suggestion leads to the absurdity of trying to disprove
the hypothesis of radiation-causation with a proposition which
would confirm it.
A Suggestion of an Opposite Nature: Denial of Co-Action
We must consider another possible explanation for the 5.67
relative rate of breast-cancer mortality. We can suppose that
non-radiation causes of breast-cancer exist in the USA which do
not exist in Japan, and that they are not co-active with each
other or with radiation. They cause breast-cancer without
involving radiation-induced lesions at all. When radiation is
added to such a "scenario," we would suppose that the effect per
rad would be the same in the USA and Japan.
For simplification, we can assume that the amount of radiation
exposure was the same in the USA and Japan before the
mid-1960s. So, the relative rate of radiation-induced
breast-cancer mortality would be 1.0. Then the excess relative
rate, from all other causes combined, would be 4.67 in the
mid-1960s. This would mean that (4.67 / 5.67), or 82.4 % of all
breast-cancer mortality in the USA was due to non-radiation
causes (internal and external) --- each acting alone, and
present in the USA but less present in Japan. This is a
possibility, neither provable nor disprovable by current
knowledge.
We think (but can not prove) that it would be a mistake to deny
the impact of co-action between cancer-causing agents. We are
very comfortable with the concept that a rad of medical
radiation has a greater impact in the USA than in Japan, due to
interaction with other factors.
o - "Lift-Off" Reduction-Factor - Column R
For the two youngest age-groups in the A-Bomb Study, the
lifespan follow-up is far from complete. In 1995, the 0-9
year-olds reach an average age of about 54 years; the 10-19
year-olds reach about 64.5 years of age, on the average
(calculated from Gofman
1990, Table 26-E). We
and others necessarily have to make assumptions about what
the full lifetime follow-up will show, as already noted
with respect to Box 2.
We know that the observed number of cancers in the low-dose
column (Box 1, Column C) will increase
after 1982, as the two youngest age-groups advance in age. We
used the observations of their older colleagues to estimate
what would happen to the number of cases in the youngest
low-dose groups. And then we applied the same factor
of increase (Box 2, Column E) to the
radiation-induced difference between high-dose and low-dose
groups (Column D). This was equivalent to
assuming that the total number of cases in the high-dose group
(Box 1, Column B) and the low-dose
group (Box 1, Column C) would increase by the same
factor. For example (150.94 x 19.11207) - (55.41 x
19.11207) = (2884.7758) - (1059) = 1825.776, which is the
first value shown in Box 2, Column F,
for "Lifetime excess."
However, we have shown in
Chapter 3, Part 4,
why this treatment
may overestimate the lifetime difference for the youngest
age-group, and possibly for the 10-19 year-olds too.
Chapter 3 explored the "lift-off"
phenomenon! By this, we mean the temporary inflation of a
disparity between two curves, if they "lift off" at
different years or at different slopes from a baseline rate
which was near zero. The inflated difference is temporary,
and becomes diluted by subsequent observations at older ages.
Because there are more "subsequent observations" to come in the
0-9 age-group than in the 10-19 age-group, we adjust the lifetime
difference in Column N more severely downward
for the 0-9 age-group than for the 10-19 age-group. In
Column R, we are going to slash the lifetime
excess in half for the 0-9 year-olds, with a
reduction-factor of 0.5; for the 10-19 year-olds, we use a
reduction-factor of 0.75; we make no adjustment for the 20-34
year-olds. Only additional follow-up data will tell whether
these "lift-off" factors are too high or too low. Meanwhile,
in view of the "lift-off" phenomenon, we feel that a correction
of some sort is indicated.
o - Conversion Factors - Column S
In Box 6, Column S provides the
conversion-factors used in our
Master Table. Each entry
is the estimated number of radiation-induced excess breast-cancer
cases (lifetime incidence) per 10,000 females (USA) from an
average breast-dose of one medical rad. The entries are the
product of Columns "O" x P x Q x R.
# # # # #
o - "Doesn't Everything Cause Cancer If the Dose Is High Enough?
This question is asked at page 8 of the National Cancer
Institute's 1990 booklet, and answered as follows:
"No. High doses of many chemicals are toxic, but they
will not cause tumors. Other forms of toxicity, such as loss of
hair or weight, various organ malfunctions, or even death, should
not be confused with carcinogenesis." And:
"In one study, 120 pesticides and industrial chemicals were
tested at the highest doses the mice could tolerate and survive.
The mice were exposed for two years. These chemicals were not
randomly selected, but were chosen because they were suspected
of carcinogenicity. However, only 11 of these chemicals caused
cancer in the test animals."
o - "What Happens When People Are Exposed to Several
Carcinogens at the Same Time?"
This question is asked at page 10 of the National Cancer
Institute's 1990 booklet, and answered as follows:
"The resulting cancer rate may be higher than would be
predicted by adding the risks from each carcinogen alone.
Cigarette smoking and asbestos exposure, for example, each cause
cancer. But asbestos workers who smoke are subject to a cancer
risk that is far higher than would be expected by adding the risk
from smoking to the risk from asbestos." And:
"Animal studies have shown similar jumps in cancer rates
from multiple exposures. This effect does not occur in animals
with all carcinogens, and sometimes two carcinogens will
somehow interact to give reduced rates of cancer. Although it is
conceivable that this type of reduction could occur with human
exposures, it is not something people can count on."
Source: National Cancer Institute (USA), "Everything
Doesn't Cause Cancer," 12-page booklet, March 1990
(NIH Publication 90-2039).
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for 1950-1982, with all ages and both sexes combined, is
reproduced here from Figure
14-E of Gofman 1990. The
curve has the same shape in the DS86 dosimetry, properly handled
with "constant-cohorts."