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Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
Appendix D
Thyroid Cancer in Idaho 1970-1996
Christopher J. Johnson, MPH, Epidemiologist
Stacey L. Carson, ART, CTR, Director
Cancer Data Registry of Idaho
PO Box 1278
Boise, Idaho 83701-1278
(208) 338-5100 ext. 213 (phone)
(208) 338-7800 (FAX)
Following release of the National Cancer Institute's report of its study to assess Americans' exposure to radioactive iodine-131 from atmospheric nuclear bomb testing in the 1950s and 1960s at the Nevada Test Site, and pursuant to requests from the public, media, and health officials, staff at the Cancer Data Registry of Idaho (CDRI) conducted several analyses of thyroid cancer. This report describes the analyses of thyroid cancer incidence rates in Idaho, 1970-1996, and the ratio of female-to-male thyroid cancer cases by age group. Because four of the five counties in the United States with highest estimated exposure to iodine-131 from atmospheric nuclear bomb tests at the Nevada Test Site are located in Idaho (Blaine, Custer, Gem, and Lemhi), and public health services are delivered at the health district level, analyses were conducted at both the county and health district levels of geography (see Appendix for listing of counties by health district).
METHODS
Established in 1969, CDRI is a population-based cancer registry that collects incidence and survival data on cancer patients who reside in the state of Idaho at the time of diagnosis or who are diagnosed and/or treated for cancer in the state of Idaho. All cases of invasive thyroid cancer diagnosed among residents of the state of Idaho between January 1, 1970, and December 31, 1996, were included in these analyses.
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Thyroid Cancer Incidence in Idaho, 1970-1996, by Birth Cohort and Overall
A combination of direct and indirect age adjustment was used to compare the incidence rates of thyroid cancer among geographic areas and by birth cohort. The following provides an overview of the steps taken in the analysis.
Step 1. The number of invasive cases of thyroid cancer diagnosed among residents of the state of Idaho, 1970-1996, were summed by sex, 5-year age group, county of residence, and year of diagnosis. The age groups were: 0-4, 5-9, 10-14, …, 85+. Cases with missing information on sex, age at diagnosis, or county were not included in the analysis. If birth year was unknown, it was imputed from diagnosis date and estimated age at diagnosis. Birth cohort was defined by birth year: before 1948, 1948-1958, and after 1958. Given the years that atmospheric nuclear bomb tests were conducted at the Nevada Test Site, and the fact that children aged 0-5 are biologically most sensitive to iodine-131, persons born during the time period 1948-1958 are thought to have been at the risk of highest exposure. The other birth cohorts were chosen for comparison purposes.
Step 2. Population data were obtained from the U.S. Bureau of the Census. Data for 1970-1989 were available by sex and 5-year age-group. Data for 1990-1996 were available by sex and single-year age group. Single-year age group estimates were derived from 1970-1989 data by dividing the population in each 5-year age group into 5 equal parts. For example, if 1,000 persons were in the 5-year age group 15-19, 200 persons each were assigned to ages 15, 16, 17, 18, and 19. Separating the population data into single-year age groups was necessary to calculate age-adjusted rates by birth cohort.
Step 3. Three birth cohorts were defined, again based upon differences due to age in estimated exposure to iodine-131 from atmospheric nuclear bomb tests at the Nevada Test Site: before 1948, 1948-1958, and after 1958. Population data were estimated for each of the birth cohorts, by county, sex, and 5-year age group. Two age breaks were defined and incremented by year of study. The lower age break was defined as: AGELOW = YEAR - 1958, and year was varied from 1970-1996, the years for which CDRI has reliable statewide case information. The upper age break was defined as: AGEHIGH = YEAR - 1948, and year was again varied from 1970-1996. AGELOW and AGEHIGH give the (truncated) ages a person would have been in each year, 1970-1996, given that they were born in the period 1948-1958. Thus, a person born from 1948-1958 would have been assigned ages 12-22 in 1970, and between 32 and 42 in 1990, etc. Population data were assigned to birth cohorts depending on single-year age group and year (1970-1996). For example, for the year 1970, persons aged 10 were assigned to the after-1958 birth cohort; persons aged 20 were assigned to the 1948-1958 birth cohort; and persons aged 30 were assigned to the before-1948 birth
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cohort. Finally, population data were collapsed over age to yield estimates by birth cohort, county, sex, and 5-year age group.
Step 4. The age-adjusted rate of invasive thyroid cancer for the state of Idaho, 1970-1996, was calculated by the direct method, using the 1970 U.S. population as standard. Age-specific rates for the state of Idaho were calculated for use in direct age adjustment. The result was an age-adjusted incidence rate of thyroid cancer for the state of Idaho, 1970-1996, of 4.22 cases per 100,000 person-years.
Step 5. Age- and sex-specific rates for the state of Idaho for the time period 1970-1996 were calculated for use as standard rates in indirect age and sex adjustment.
Step 6. For all birth cohorts combined, the numbers of observed and expected cases were calculated for each health district and county. Expected cases were calculated by applying the age- and sex-specific rates for the state of Idaho to the population by age and sex in each health district and county. Two-tailed p-values comparing the number of observed and expected cases were calculated using the Poisson probability distribution. Observed and expected cases, and p-values, were calculated separately for males, females, and both sexes combined.
Step 7. The adjusted incidence rates for each health district and county were calculated as the standardized incidence ratio (observed/expected) multiplied by the age-adjusted rate from Step 4. For example, there were 314 cases observed, and 254.6 cases expected in Health District 4, yielding an adjusted incidence rate of (314/254.6) * 4.22 = 5.20 cases per 100,000 person-years.
Step 8. Age- and sex-specific rates for the state of Idaho, 1970-1996, were calculated by birth cohort for use in indirect age and sex adjustment by birth cohort. (Step 5 was repeated by birth cohort.)
Step 9. For each birth cohort, the number of observed and expected cases were calculated for each health district and county. Expected cases were calculated by applying the age- and sex-specific rates for the state of Idaho, by birth cohort (from Step 8), to the population by age and sex in each health district and county. Two-tailed p-values comparing the number of observed and expected cases were calculated using the Poisson probability distribution. Observed and expected cases, and p-values, were calculated separately for males, females, and both sexes combined, by birth cohort. Statistical significance was set at α = .05.
Step 10. The adjusted rates for each health district and county were calculated by birth cohort as the standardized incidence ratio for that birth cohort (observed/expected) multiplied by the age-adjusted rate for all birth cohorts (from Step 4). For example, there were 87 cases observed and 69.4 expected in Health District 4
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for the birth cohort 1948-1958, yielding an adjusted incidence rate of (87/69.4) * 4.22 = 5.29. The overall rate from Step 4 was used as the reference rate in order to facilitate comparisons across birth cohort for individual health districts and counties, and to allow comparisons among health districts and counties within birth cohort. See Box D.1 for a description of the Idaho population by health districts.
Step 11. The adjusted rates for the state of Idaho were calculated by birth cohort using the standardized incidence ratio for that birth cohort (observed/expected), with expected cases based upon age- and sex-specific rates for all birth cohorts
BOX D.1 Description of Idaho Population
The population of the state of Idaho in 1996 was estimated to be 1,189,251, made up of 594,604 males and 594,647 females (U.S. Bureau of the Census). Idaho comprises 44 counties grouped into seven health districts. The composition of the health districts and population estimates by sex are shown below:
District
Counties
Males
Females
District 1
Benewah, Bonner, Boundary, Kootenai, Shoshone
80,792
81,548
District 2
Clearwater, Idaho, Latah, Lewis, Nez Perce
49,574
48,568
District 3
Adams, Canyon, Gem, Owyhee, Payette, Washington
84,753
85,602
District 4
Ada, Boise, Elmore, Valley
147,684
149,119
District 5
Blaine, Camas, Cassia, Gooding, Jerome, Lincoln, Minidoka, Twin Falls
77,788
77,139
District 6
Bannock, Bear Lake, Bingham, Butte, Caribou, Franklin, Oneida, Power
77,425
77,227
District 7
Bonneville, Clark, Custer, Fremont, Jefferson, Lemhi, Madison, Teton
76,588
75,444
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(from Step 5). For example, there were 271 cases observed and 256.9 expected in the state of Idaho, 1970-1996, among the 1948-1958 cohort, yielding an adjusted incidence rate of (271/256.9) * 4.22 = 4.45 cases per 100,000 person-years. The state of Idaho rates by birth cohort were designed to be compared to each other, and to the overall state of Idaho rate of 4.22 cases per 100,000 person-years.
Ratio of Female-to-Male Thyroid Cancer Cases by Age Group and Birth Cohort
The overall ratio of thyroid cancer cases among females versus males differed by birth cohort, with a ratio of 2.7 in the before-1948 cohort, 5.2 in the 1948-1958 cohort, and 5.3 in the after-1958 cohort. In order to examine if the differences in female-to-male ratios by birth cohort were an artifact of differing age-specific rates by sex, cumulative ratios of female-to-male cases were calculated by age group. For all invasive cases of thyroid cancer diagnosed among Idaho residents, 1970-1996, the numbers of cases were summed separately for males and females by 5-year age group and birth cohort. The cumulative ratios of female-to-male cases were calculated by 5-year age group and birth cohort. For example, for the age group 35-39, the cumulative female-to-male ratio in the before-1948 birth cohort was 5.0 (75 cases among females aged 39 years and younger, and 15 cases among males aged 39 years and younger).
RESULTS
The overall age-adjusted incidence rate of invasive thyroid cancer in Idaho, 1970-1996, was 4.22 cases per 100,000 person-years (see Table D.1). Incidence rates varied by geographic location, ranging from 3.28 cases per 100,000 person-years in Health District 2 to 5.20 cases per 100,000 person-years in Health District 4. There were significantly more cases of invasive thyroid cancer diagnosed among residents of Health District 4 than expected based upon rates in the state of Idaho (314 observed, 254.6 expected, p<.001), and the number of observed cases was higher than expected for both males and females. Ada County had significantly more cases of invasive thyroid cancer than expected based upon rates in the state of Idaho (276 observed, 221.4 expected, p<.001). None of the four Idaho counties with highest estimated exposure to iodine-131 showed an elevation in thyroid cancer cases from 1970-1996.
Among the birth cohort born before 1948, the incidence rate of invasive thyroid cancer, 1970-1996, was 4.10 cases per 100,000 person-years (see Table D.2). There were significantly more cases observed than expected in Health District 4 and Ada County. None of the four Idaho counties with highest estimated exposure to iodine-131 showed an elevation in thyroid cancer cases from 1970-1996 in the birth cohort born before 1948.
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Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
Among the birth cohort born 1948-1958, the incidence rate of invasive thyroid cancer, 1970-1996, was 4.45 cases per 100,000 person-years (see Table D.3). There were significantly more cases observed than expected in Health District 4 and Ada County. None of the four Idaho counties with highest estimated exposure to iodine-131 showed an elevation in thyroid cancer cases from 1970-1996 in the birth cohort born 1948-1958. Although the incidence rate of invasive thyroid cancer, 1970-1996, was highest for the birth cohort born 1948-1958, the number of cases observed was not statistically significantly different from that expected based upon rates for all birth cohorts.
Among the birth cohort born after 1958, the incidence rate of invasive thyroid cancer, 1970-1996, was 4.35 cases per 100,000 person-years (see Table D.4). There were significantly more cases observed than expected in Elmore County. None of the four counties with highest estimated exposure to iodine-131 showed an elevation in thyroid cancer cases from 1970-1996 in the birth cohort born after 1958.
Regarding the female-to-male ratios for invasive thyroid cancer cases, the differences in the overall female-to-male ratios by birth cohort (see Table D.5) appear to be due to the higher age-specific thyroid cancer incidence rates in younger females as compared with younger males. In all three birth cohorts, the cumulative age-specific ratios were similar for the age groups 25-29, 30-34, and 35-39 (the only age groups for which comparisons are available across all three birth cohorts, as CDRI has reliable statewide cancer incidence data since 1970).
SUMMARY AND CONCLUSIONS
Thyroid cancer is relatively rare among all cancers, accounting for less than 2% of invasive cases in Idaho in 1996. The age-adjusted incidence rate of invasive thyroid cancer in Idaho, 1970-1996, was 4.22 cases per 100,000 person-years. In comparison, the Surveillance, Epidemiology, and End Results (SEER) rate for whites, 1973-1995, was 4.39 cases per 100,000 person-years. CDRI investigated thyroid cancer incidence in three birth cohorts to explore the relationship between age at the time of iodine-131 release from atmospheric nuclear bomb tests at the Nevada Test Site and thyroid cancer incidence. The number of invasive thyroid cancer cases in the state of Idaho, 1970-1996, was not statistically significantly higher than expected, based upon overall rates, for any of the three birth cohorts. Within each birth cohort, and for all cohorts combined, variation existed among health districts and counties in the incidence of thyroid cancer, with more marked variation observed among geographic areas with smaller populations.
There are several limitations of the data that may have influenced the results of the analyses. The accuracy of the estimated incidence rates assumes similar case
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Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
TABLE D.1 Invasive Thyroid Cancer in Idaho, 1970-1996, Among All Birth Cohorts
All Cases
Male Cases
Female Cases
Residence
Incidence Rate
Observed
Expected
P-Value
Observed
Expected
P-Value
Observed
Expected
P-Value
STATE OF IDAHO
4.22
1,119
n/a
n/a
256
n/a
n/a
863
n/a
n/a
HEALTH DISTRICT 1
3.60
127
148.9
0.074
26
35.2
0.132
101
113.7
0.250
HEALTH DISTRICT 2
3.28
85
109.4
0.018
18
25.8
0.141
67
83.6
0.072
HEALTH DISTRICT 3
4.34
165
160.6
0.751
39
37.4
0.838
126
123.2
0.826
HEALTH DISTRICT 4
5.20
314
254.6
0.000
70
55.5
0.067
244
199.2
0.002
HEALTH DISTRICT 5
4.59
171
157.2
0.291
37
36.9
1.000
134
120.3
0.232
HEALTH DISTRICT 6
3.52
126
151.0
0.042
34
34.3
1.000
92
116.7
0.021
HEALTH DISTRICT 7
4.03
131
137.2
0.631
32
30.9
0.897
99
106.3
0.515
ADA
5.26
276
221.4
0.000
63
47.7
0.039
213
173.7
0.004
ADAMS
4.13
4
4.1
1.000
2
1.1
0.570
2
3.0
0.834
BANNOCK
4.19
72
72.5
1.000
17
15.8
0.828
55
56.7
0.894
BEAR LAKE
4.64
8
7.3
0.887
2
1.8
1.000
6
5.5
0.949
BENEWAH
2.67
6
9.5
0.333
1
2.4
0.624
5
7.1
0.578
BINGHAM
3.29
30
38.5
0.190
11
8.9
0.553
19
29.7
0.050
BLAINE
4.80
16
14.1
0.674
4
3.2
0.783
12
10.9
0.815
BOISE
4.42
4
3.8
1.000
2
1.0
0.510
2
2.8
0.916
BONNER
3.40
25
31.0
0.322
6
7.6
0.733
19
23.4
0.424
BONNEVILLE
4.31
75
73.5
0.888
14
16.3
0.685
61
57.2
0.648
BOUNDARY
5.13
11
9.0
0.598
4
2.2
0.362
7
6.8
1.000
BUTTE
2.38
2
3.5
0.626
1
0.9
1.000
1
2.6
0.519
CAMAS
0.00
—
0.9
0.793
—
0.2
1.000
—
0.7
1.000
CANYON
4.67
113
102.1
0.305
28
23.1
0.354
85
79.0
0.532
CARIBOU
2.08
4
8.1
0.184
—
1.9
0.299
4
6.2
0.510
CASSIA
3.37
17
21.3
0.421
5
5.0
1.000
12
16.3
0.348
CLARK
0.00
—
0.9
0.821
—
0.3
1.000
—
0.6
1.000
CLEARWATER
3.93
11
11.8
0.969
2
3.0
0.843
9
8.8
1.000
CUSTER
7.91
9
4.8
0.112
5
1.2
0.017
4
3.6
0.957
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All Cases
Male Cases
Female Cases
Residence
Incidence Rate
Observed
Expected
P-Value
Observed
Expected
P-Value
Observed
Expected
P-Value
ELMORE
4.40
23
22.0
0.894
2
5.0
0.251
21
17.1
0.396
FRANKLIN
0.88
2
9.6
0.008
1
2.3
0.641
1
7.3
0.012
FREMONT
3.34
9
11.4
0.600
—
2.7
0.130
9
8.7
0.996
GEM
4.66
16
14.5
0.757
3
3.5
1.000
13
10.9
0.607
GOODING
3.87
13
14.2
0.888
3
3.6
1.000
10
10.6
1.000
IDAHO
2.47
10
17.1
0.094
1
4.3
0.140
9
12.8
0.363
JEFFERSON
2.90
11
16.0
0.255
4
3.8
1.000
7
12.2
0.164
JEROME
4.85
20
17.4
0.594
4
4.1
1.000
16
13.3
0.519
KOOTENAI
3.53
66
78.9
0.156
11
18.1
0.105
55
60.8
0.501
LATAH
3.40
27
33.5
0.295
6
7.4
0.771
21
26.1
0.372
LEMHI
4.29
9
8.9
1.000
2
2.2
1.000
7
6.6
0.989
LEWIS
0.87
1
4.8
0.092
—
1.2
0.580
1
3.6
0.249
LINCOLN
3.13
3
4.0
0.850
—
1.0
0.713
3
3.0
1.000
MADISON
4.17
18
18.2
1.000
7
3.5
0.134
11
14.7
0.409
MINIDOKA
4.51
23
21.5
0.806
1
5.1
0.074
22
16.4
0.216
NEZ PERCE
3.61
36
42.1
0.394
9
9.7
0.980
27
32.3
0.400
ONEIDA
3.21
3
3.9
0.889
—
1.0
0.749
3
3.0
1.000
OWYHEE
2.76
6
9.2
0.381
1
2.3
0.647
5
6.9
0.639
PAYETTE
3.21
15
19.7
0.344
1
4.7
0.106
14
15.0
0.924
POWER
2.82
5
7.5
0.486
2
1.7
1.000
3
5.7
0.352
SHOSHONE
3.92
19
20.4
0.863
4
4.9
0.902
15
15.5
1.000
TETON
0.00
—
3.6
0.053
—
0.9
0.808
—
2.7
0.131
TWIN FALLS
5.22
79
63.8
0.073
20
14.7
0.216
59
49.1
0.187
VALLEY
6.33
11
7.3
0.248
3
1.8
0.531
8
5.5
0.393
WASHINGTON
4.20
11
11.0
1.000
4
2.7
0.581
7
8.3
0.817
NOTES: The incidence rate for the state of Idaho is age adjusted to the standard 1970 U.S. population using the direct method. The incidence rates for the other geographic areas are the products of the standardized incidence ratios and the state age-adjusted rate. Expected cases are based upon age- and sex-specific rates for the state of Idaho. P-values compare observed and expected cases, are two-tailed, based upon the Poisson probability distribution.
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TABLE D.2 Invasive Thyroid Cancer in Idaho, 1970-1996, Among Birth Cohort Born Before 1948
All Cases
Male Cases
Female Cases
Residence
Incidence Rate
Observed
Expected
P-Value
Observed
Expected
P-Value
Observed
Expected
P-Value
STATE OF IDAHO
4.10
679
698.3
0.480
185
186.5
0.953
494
511.8
0.447
HEALTH DISTRICT 1
3.55
79
93.8
0.133
21
26.4
0.346
58
67.5
0.273
HEALTH DISTRICT 2
3.08
50
68.5
0.024
13
19.1
0.190
37
49.4
0.082
HEALTH DISTRICT 3
4.32
106
103.6
0.841
31
28.4
0.669
75
75.3
1.000
HEALTH DISTRICT 4
5.13
173
142.3
0.014
44
37.3
0.306
129
105.0
0.026
HEALTH DISTRICT 5
4.54
108
100.3
0.468
25
27.6
0.716
83
72.8
0.255
HEALTH DISTRICT 6
3.77
81
90.7
0.334
27
24.6
0.682
54
66.1
0.147
HEALTH DISTRICT 7
4.34
82
79.8
0.837
24
21.8
0.688
58
58.0
1.000
ADA
5.35
157
123.9
0.005
40
32.2
0.201
117
91.8
0.013
ADAMS
6.22
4
2.7
0.578
2
0.8
0.403
2
1.9
1.000
BANNOCK
4.41
43
41.2
0.815
13
10.9
0.595
30
30.3
1.000
BEAR LAKE
5.10
6
5.0
0.755
2
1.4
0.805
4
3.6
0.960
BENEWAH
3.45
5
6.1
0.854
1
1.8
0.915
4
4.3
1.000
BINGHAM
4.13
23
23.5
1.000
10
6.4
0.230
13
17.1
0.393
BLAINE
3.60
6
7.0
0.888
—
1.9
0.288
6
5.1
0.803
BOISE
5.52
3
2.3
0.805
2
0.7
0.319
1
1.6
1.000
BONNER
3.20
15
19.8
0.339
5
5.7
0.983
10
14.0
0.347
BONNEVILLE
4.35
44
42.7
0.882
8
11.3
0.420
36
31.4
0.459
BOUNDARY
6.62
9
5.7
0.254
3
1.6
0.458
6
4.1
0.459
BUTTE
0.00
—
2.4
0.187
—
0.7
0.990
—
1.7
0.377
CAMAS
0.00
—
0.6
1.000
—
0.2
1.000
—
0.4
1.000
CANYON
4.63
70
63.8
0.472
21
17.1
0.397
49
46.8
0.783
CARIBOU
1.65
2
5.1
0.232
—
1.4
0.494
2
3.7
0.567
CASSIA
3.13
10
13.5
0.422
4
3.7
1.000
6
9.8
0.286
CLARK
0.00
—
0.6
1.000
—
0.2
1.000
—
0.4
1.000
CLEARWATER
3.72
7
7.9
0.922
2
2.3
1.000
5
5.6
1.000
CUSTER
6.79
5
3.1
0.406
3
0.9
0.140
2
2.2
1.000
OCR for page 207
Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
All Cases
Male Cases
Female Cases
Residence
Incidence Rate
Observed
Expected
P-Value
Observed
Expected
P-Value
Observed
Expected
P-Value
ELMORE
2.56
7
11.6
0.222
—
3.1
0.091
7
8.5
0.781
FRANKLIN
0.00
—
6.4
0.003
—
1.8
0.330
—
4.6
0.021
FREMONT
2.92
5
7.2
0.543
—
2.0
0.261
5
5.2
1.000
GEM
3.82
9
9.9
0.930
3
2.8
1.000
6
7.1
0.864
GOODING
4.28
10
9.9
1.000
3
2.8
1.000
7
7.0
1.000
IDAHO
2.55
7
11.6
0.216
1
3.4
0.298
6
8.2
0.573
JEFFERSON
3.48
8
9.7
0.735
4
2.8
0.598
4
6.9
0.357
JEROME
5.63
15
11.2
0.329
4
3.1
0.770
11
8.1
0.389
KOOTENAI
3.32
38
48.4
0.148
8
13.3
0.176
30
35.1
0.446
LATAH
2.83
12
17.9
0.192
3
4.9
0.562
9
13.0
0.333
LEMHI
4.20
6
6.0
1.000
2
1.8
1.000
4
4.3
1.000
LEWIS
1.24
1
3.4
0.292
—
1.0
0.741
1
2.4
0.610
LINCOLN
1.55
1
2.7
0.490
—
0.8
0.898
1
1.9
0.856
MADISON
7.13
14
8.3
0.087
7
2.2
0.014
7
6.1
0.821
MINIDOKA
3.71
12
13.6
0.790
—
3.8
0.044
12
9.8
0.568
NEZ PERCE
3.51
23
27.6
0.440
7
7.5
1.000
16
20.1
0.425
ONEIDA
3.02
2
2.8
0.943
—
0.8
0.908
2
2.0
1.000
OWYHEE
3.55
5
6.0
0.907
1
1.8
0.948
4
4.2
1.000
PAYETTE
3.18
10
13.3
0.457
1
3.7
0.237
9
9.6
1.000
POWER
4.73
5
4.5
0.923
2
1.2
0.709
3
3.2
1.000
SHOSHONE
3.66
12
13.9
0.746
4
3.9
1.000
8
10.0
0.673
TETON
0.00
—
2.2
0.225
—
0.6
1.000
—
1.5
0.429
TWIN FALLS
5.47
54
41.7
0.076
14
11.2
0.467
40
30.5
0.114
VALLEY
5.66
6
4.5
0.584
2
1.3
0.743
4
3.2
0.784
WASHINGTON
4.27
8
7.9
1.000
3
2.2
0.766
5
5.7
0.997
NOTES: The incidence rate for the state of Idaho is the product of the age adjusted rate for all birth cohorts using the 1970 standard U.S. population (direct age adjustment) and the standardized incidence ratio for this birth cohort compared with all birth cohorts (indirect age adjustment). The incidence rates for the other geographic areas are the products of the standardized incidence ratios for this cohort and the state age-adjusted rate. Expected cases for geography other than state are based upon age- and sex-specific rates for the state of Idaho for this cohort. P-values compare observed and expected cases, are two-tailed, based upon the Poisson probability distribution.
OCR for page 208
Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
TABLE D.3 Invasive Thyroid Cancer in Idaho, 1970-1996, Among Birth Cohort Born 1948-1958
All Cases
Male Cases
Female Cases
Residence
Incidence Rate
Observed
Expected
P-Value
Observed
Expected
P-Value
Observed
Expected
P-Value
STATE OF IDAHO
4.45
271
256.9
0.394
44
45.2
0.932
227
211.6
0.307
HEALTH DISTRICT 1
3.18
27
35.8
0.156
4
5.7
0.654
23
30.1
0.223
HEALTH DISTRICT 2
4.10
24
24.7
0.992
3
4.2
0.804
21
20.6
0.980
HEALTH DISTRICT 3
4.35
36
35.0
0.905
6
5.5
0.950
30
29.4
0.966
HEALTH DISTRICT 4
5.29
87
69.4
0.046
16
11.4
0.227
71
58.0
0.109
HEALTH DISTRICT 5
4.38
37
35.6
0.865
5
5.8
0.948
32
29.8
0.737
HEALTH DISTRICT 6
3.44
30
36.8
0.297
7
6.0
0.775
23
30.8
0.177
HEALTH DISTRICT 7
3.76
30
33.7
0.599
3
5.5
0.413
27
28.2
0.919
ADA
5.39
77
60.3
0.043
13
9.7
0.361
64
50.6
0.078
ADAMS
0.00
—
0.9
0.824
—
0.1
1.000
—
0.7
0.953
BANNOCK
4.20
19
19.1
1.000
4
3.1
0.741
15
16.0
0.930
BEAR LAKE
2.94
1
1.4
1.000
—
0.2
1.000
1
1.2
1.000
BENEWAH
0.00
—
2.2
0.228
—
0.4
1.000
—
1.8
0.329
BINGHAM
1.39
3
9.1
0.040
1
1.5
1.000
2
7.6
0.036
BLAINE
3.59
4
4.7
0.987
—
0.8
0.887
4
3.9
1.000
BOISE
4.15
1
1.0
1.000
—
0.2
1.000
1
0.8
1.000
BONNER
3.90
7
7.6
1.000
1
1.2
1.000
6
6.3
1.000
BONNEVILLE
4.28
19
18.7
1.000
3
3.0
1.000
16
15.7
1.000
BOUNDARY
3.96
2
2.1
1.000
1
0.4
0.594
1
1.8
0.940
BUTTE
11.27
2
0.7
0.346
1
0.1
0.240
1
0.6
0.925
CAMAS
0.00
—
0.2
1.000
—
0.0
1.000
—
0.2
1.000
CANYON
4.53
25
23.3
0.774
5
3.7
0.613
20
19.6
0.988
CARIBOU
4.43
2
1.9
1.000
—
0.3
1.000
2
1.6
0.946
CASSIA
4.46
5
4.7
1.000
1
0.8
1.000
4
4.0
1.000
CLARK
0.00
—
0.2
1.000
—
0.0
1.000
—
0.1
1.000
CLEARWATER
6.78
4
2.5
0.480
—
0.4
1.000
4
2.1
0.311
CUSTER
7.50
2
1.1
0.621
—
0.2
1.000
2
0.9
0.480
OCR for page 209
Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
All Cases
Male Cases
Female Cases
Residence
Incidence Rate
Observed
Expected
P-Value
Observed
Expected
P-Value
Observed
Expected
P-Value
ELMORE
3.46
5
6.1
0.862
2
1.2
0.645
3
4.9
0.549
FRANKLIN
4.42
2
1.9
1.000
1
0.3
0.550
1
1.6
1.000
FREMONT
3.37
2
2.5
1.000
—
0.4
1.000
2
2.1
1.000
GEM
7.37
5
2.9
0.325
—
0.4
1.000
5
2.4
0.196
GOODING
4.64
3
2.7
1.000
—
0.5
1.000
3
2.3
0.793
IDAHO
2.38
2
3.5
0.626
—
0.6
1.000
2
2.9
0.879
JEFFERSON
2.23
2
3.8
0.541
—
0.6
1.000
2
3.2
0.777
JEROME
4.39
4
3.8
1.000
—
0.6
1.000
4
3.2
0.805
KOOTENAI
3.01
14
19.6
0.240
2
3.1
0.818
12
16.6
0.316
LATAH
5.28
11
8.8
0.541
2
1.6
0.918
9
7.2
0.608
LEMHI
2.25
1
1.9
0.880
—
0.3
1.000
1
1.6
1.000
LEWIS
0.00
—
0.9
0.803
—
0.2
1.000
—
0.8
0.939
LINCOLN
0.00
—
0.8
0.858
—
0.1
1.000
—
0.7
0.997
MADISON
3.70
4
4.6
1.000
—
0.7
0.983
4
3.9
1.000
MINIDOKA
7.05
8
4.8
0.224
—
0.8
0.900
8
4.0
0.101
NEZ PERCE
3.29
7
9.0
0.654
1
1.4
1.000
6
7.6
0.742
ONEIDA
5.84
1
0.7
1.000
—
0.1
1.000
1
0.6
0.909
OWYHEE
2.14
1
2.0
0.829
—
0.3
1.000
1
1.6
1.000
PAYETTE
2.11
2
4.0
0.477
—
0.6
1.000
2
3.4
0.686
POWER
0.00
—
1.9
0.301
—
0.3
1.000
—
1.6
0.411
SHOSHONE
3.94
4
4.3
1.000
—
0.7
1.000
4
3.6
0.970
TETON
0.00
—
0.9
0.821
—
0.2
1.000
—
0.7
0.960
TWIN FALLS
3.98
13
13.8
0.971
4
2.2
0.358
9
11.6
0.556
VALLEY
8.51
4
2.0
0.280
1
0.3
0.569
3
1.6
0.458
WASHINGTON
6.40
3
2.0
0.635
1
0.3
0.544
2
1.7
0.990
NOTES: The incidence rate for the state of Idaho is the product of the age adjusted rate for all birth cohorts using the 1970 standard U.S. population (direct age adjustment) and the standardized incidence ratio for this birth cohort compared with all birth cohorts (indirect age adjustment). The incidence rates for the other geographic areas are the products of the standardized incidence ratios for this cohort and the state age-adjusted rate. Expected cases for geography other than state are based upon age- and sex-specific rates for the state of Idaho for this cohort. P-values compare observed and expected cases, are two-tailed, based upon the Poisson probability distribution.
OCR for page 210
Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
TABLE D.4 Invasive Thyroid Cancer in Idaho, 1970-1996, Among Birth Cohort Born After 1958
All Cases
Male Cases
Female Cases
Residence
Incidence Rate
Observed
Expected
P-Value
Observed
Expected
P-Value
Observed
Expected
P-Value
STATE OF IDAHO
4.35
169
163.9
0.708
27
24.3
0.634
142
139.6
0.859
HEALTH DISTRICT 1
4.57
21
19.4
0.774
1
3.1
0.367
20
16.3
0.416
HEALTH DISTRICT 2
2.92
11
15.9
0.265
2
2.5
1.000
9
13.4
0.282
HEALTH DISTRICT 3
4.41
23
22.0
0.887
2
3.5
0.631
21
18.5
0.615
HEALTH DISTRICT 4
5.20
54
43.8
0.152
10
6.9
0.329
44
36.9
0.279
HEALTH DISTRICT 5
5.20
26
21.1
0.336
7
3.5
0.137
19
17.6
0.793
HEALTH DISTRICT 6
2.74
15
23.1
0.099
—
3.7
0.050
15
19.4
0.375
HEALTH DISTRICT 7
3.39
19
23.6
0.398
5
3.7
0.621
14
20.0
0.213
ADA
4.66
42
38.1
0.565
10
5.9
0.159
32
32.1
1.000
ADAMS
0.00
—
0.5
1.000
—
0.1
1.000
—
0.4
1.000
BANNOCK
3.49
10
12.1
0.678
—
1.8
0.321
10
10.2
1.000
BEAR LAKE
4.92
1
0.9
1.000
—
0.1
1.000
1
0.7
1.000
BENEWAH
3.60
1
1.2
1.000
—
0.2
1.000
1
1.0
1.000
BINGHAM
2.89
4
5.9
0.611
—
1.0
0.747
4
4.9
0.928
BLAINE
10.53
6
2.4
0.072
4
0.4
0.002
2
2.0
1.000
BOISE
0.00
—
0.5
1.000
—
0.1
1.000
—
0.4
1.000
BONNER
3.41
3
3.7
0.984
—
0.6
1.000
3
3.1
1.000
BONNEVILLE
4.23
12
12.0
1.000
3
2.0
0.648
9
10.0
0.922
BOUNDARY
0.00
—
1.2
0.621
—
0.2
1.000
—
1.0
0.759
BUTTE
0.00
—
0.4
1.000
—
0.1
1.000
—
0.3
1.000
CAMAS
0.00
—
0.1
1.000
—
0.0
1.000
—
0.1
1.000
CANYON
5.04
18
15.1
0.514
2
2.4
1.000
16
12.7
0.420
CARIBOU
0.00
—
1.1
0.693
—
0.2
1.000
—
0.9
0.828
CASSIA
2.86
2
3.0
0.867
—
0.5
1.000
2
2.5
1.000
CLARK
0.00
—
0.1
1.000
—
0.0
1.000
—
0.1
1.000
CLEARWATER
0.00
—
1.3
0.566
—
0.2
1.000
—
1.0
0.713
CUSTER
14.82
2
0.6
0.224
2
0.1
0.009
—
0.5
1.000
OCR for page 211
Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
All Cases
Male Cases
Female Cases
Residence
Incidence Rate
Observed
Expected
P-Value
Observed
Expected
P-Value
Observed
Expected
P-Value
ELMORE
10.58
11
4.4
0.011
—
0.8
0.918
11
3.6
0.003
FRANKLIN
0.00
—
1.3
0.538
—
0.2
1.000
—
1.1
0.671
FREMONT
5.22
2
1.6
0.961
—
0.3
1.000
2
1.3
0.767
GEM
5.11
2
1.7
0.984
—
0.3
1.000
2
1.4
0.796
GOODING
0.00
—
1.6
0.405
—
0.3
1.000
—
1.3
0.539
IDAHO
2.23
1
1.9
0.870
—
0.3
1.000
1
1.6
1.000
JEFFERSON
1.69
1
2.5
0.574
—
0.4
1.000
1
2.1
0.771
JEROME
1.83
1
2.3
0.659
—
0.4
1.000
1
1.9
0.858
KOOTENAI
5.26
14
11.2
0.480
1
1.8
0.950
13
9.5
0.321
LATAH
2.47
4
6.8
0.376
1
1.0
1.000
3
5.8
0.332
LEMHI
9.16
2
0.9
0.471
—
0.1
1.000
2
0.8
0.365
LEWIS
0.00
—
0.5
1.000
—
0.1
1.000
—
0.4
1.000
LINCOLN
18.17
2
0.5
0.159
—
0.1
1.000
2
0.4
0.115
MADISON
0.00
—
5.4
0.009
—
0.6
1.000
—
4.8
0.017
MINIDOKA
4.16
3
3.0
1.000
1
0.5
0.797
2
2.5
1.000
NEZ PERCE
4.69
6
5.4
0.906
1
0.8
1.000
5
4.6
0.957
ONEIDA
0.00
—
0.4
1.000
—
0.1
1.000
—
0.4
1.000
OWYHEE
0.00
—
1.3
0.572
—
0.2
1.000
—
1.0
0.723
PAYETTE
5.22
3
2.4
0.873
—
0.4
1.000
3
2.0
0.668
POWER
0.00
—
1.1
0.643
—
0.2
1.000
—
0.9
0.775
SHOSHONE
5.98
3
2.1
0.710
—
0.3
1.000
3
1.8
0.525
TETON
0.00
—
0.6
1.000
—
0.1
1.000
—
0.5
1.000
TWIN FALLS
6.16
12
8.2
0.258
2
1.3
0.771
10
6.9
0.318
VALLEY
4.82
1
0.9
1.000
—
0.1
1.000
1
0.7
1.000
WASHINGTON
0.00
—
1.1
0.645
—
0.2
1.000
—
1.0
0.772
NOTES: The incidence rate for the state of Idaho is the product of the age adjusted rate for all birth cohorts using the 1970 standard U.S. population (direct age adjustment) and the standardized incidence ratio for this birth cohort compared with all birth cohorts (indirect age adjustment). The incidence rates for the other geographic areas are the products of the standardized incidence ratios for this cohort and the state age-adjusted rate. Expected cases for geography other than state are based upon age- and sex-specific rates for the state of Idaho for this cohort. P-values compare observed and expected cases, are two-tailed, based upon the Poisson probability distribution.
OCR for page 212
Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
TABLE D.5 Ratio of Female-to-Male Invasive Thyroid Cancer Cases by Age Group and Birth Cohort
Birth Cohort Born Before 1948
Birth Cohort Born 1948-1958
Birth Cohort Born After 1958
Age
Group
Female Cases
Male Cases
Cumulative F:M Ratio
Female Cases
Male Cases
Cumulative F:M Ratio
Female Cases
Male Cases
Cumulative F:M Ratio
0- 4
0
1
0.0
5- 9
2
0
2.0
10-14
5
3
1.8
15-19
7
2
3.5
21
3
4.0
20-24
22
5
4.1
42
3
7.0
25-29
8
1
8.0
37
3
6.6
44
9
6.0
30-34
33
4
8.2
58
9
6.5
25
5
5.8
35-39
34
10
5.0
50
14
5.3
3
3
5.3
40-44
52
20
3.6
42
11
4.9
45-49
70
15
3.9
11
0
5.2
50-54
55
23
3.5
55-59
60
20
3.4
60-64
50
29
3.0
65-69
37
17
2.9
70-74
37
22
2.7
75-79
30
12
2.7
80-84
16
10
2.6
85+
12
2
2.7
Total
494
185
2.7
227
44
5.2
142
27
5.3
OCR for page 213
Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
ascertainment rates across geographic areas, and depends upon the accuracy of the population estimates generated by the U.S. Bureau of the Census and apportionment of 5-year age group data into five equal single-year groups. The analyses did not account for in- or out-migration of cases. Cases among previous Idaho residents who moved to another state prior to diagnosis were not accounted for, but cases among persons who previously resided in other states, but moved to Idaho prior to diagnosis, were counted as Idaho cases. This same limitation exists at the county level for county-specific analyses. Many of the statistics, particularly for the county analyses by birth cohort, are based upon small numbers of cases. Incidence rates based upon 10 or fewer cases (numerator) should be interpreted with caution.
None of the four Idaho counties with highest estimated exposure to iodine-131 showed an elevation in thyroid cancer cases from 1970-1996 in the birth cohort born during 1948-1958, which was estimated to have received the highest exposure to iodine-131. Although the overall female-to-male thyroid case ratios differed by birth cohort, this result was confounded by age, as the cumulative age-specific ratios are similar in each birth cohort.
Representative terms from entire chapter:
thyroid cancer