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19 March 2010

Answer to Question #487 Submitted to "Ask the Experts"

Category: Radiation Effects — Dose Response

The following question was answered by an expert in the appropriate field:

I would like a list of cancers considered to be radiogenic and the dose that likely would double the mortality from each cancer.

Column 1 of the following table is a list of the sites of cancers that, at the time Federal Guidance Report No. 13 (EPA 1999) was being prepared, were considered to be radiogenic and for which at least a nominal radiation risk coefficient could be estimated. The lifetime cancer mortality risks based on the same 1989-1991 vital statistics used for FGR-13 are shown in Column 2. Using the average radiation mortality risk coefficients from FGR-13 in Column 3, doubling doses (Column 4) can be calculated as the quotient of the corresponding entries in Columns 2 and 3.

Radiogenic Cancers
Site	Baseline Mortality	Risk Coefficient (1/Sv)	Doubling Dose (Sv)	Risk at 3.9 Sv
Esophagus	4.2E-03	1.2E-03	3.6E+00	4.5E-03
Stomach	6.4E-03	4.1E-03	1.6E+00	1.6E-02
Colon	2.2E-02	1.0E-02	2.1E+00	4.0E-02
Liver	3.7E-03	1.5E-03	2.5E+00	5.8E-03
Lung	6.0E-02	9.9E-03	6.1E+00	3.8E-02
Bone	4.1E-04	9.5E-05	4.4E+00	3.7E-04
Skin	1.0E-03	1.0E-04	1.0E+01	3.9E-04
Breast	1.8E-02	5.1E-03	3.5E+00	2.0E-02
Ovary	5.1E-03	1.5E-03	3.4E+00	5.8E-03
Bladder	5.1E-03	2.4E-03	2.1E+00	9.2E-03
Kidney	4.3E-03	5.1E-04	8.4E+00	2.0E-03
Thyroid	4.4E-04	3.2E-04	1.4E+00	1.3E-03
Leukemia	6.3E-03	5.6E-03	1.1E+00	2.2E-02
Residual	8.4E-02	1.5E-02	5.7E+00	5.8E-02
Total	2.2E-01	5.8E-02	3.9E+00	2.2E-01

Because the risk coefficients are estimates for low dose or low dose rate exposures, the doubling doses would be for a protracted exposure. Of course, doubling the force of mortality for a given cancer would reduce life expectancy so that the expected cancer risk would be less than twice the original baseline value. Column 5 shows the calculated risk of 3.9 Sv to each organ or tissue. This dose would provide a total radiation risk equal to the baseline total risk although there is substantial variation in the risk at each site. Again, the effects of dose rate and shortened life expectancy have not been considered. Reference: EPA 1999. Cancer Risk Coefficients for Environmental Exposure to Radionuclides, Federal Guidance Report No.13, EPA 402-R-99-001, U.S. Environmental Protection Agency, Washington DC, September 1999. Available at the EPA Web site.

Christopher B. Nelson
EPA/ORIA/RPD Phone: 202-564-9209

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