Dose Response Curve

Dose response curves are graphical representations of the changes in biological effect with changes in dose. Dose response curves can be used to estimate the biological effect related to a particular radiation dose so that one can then estimate the risk associated with a particular dose.

Radiation is like most substances that cause cancer since the effects are apparent at high doses, but not at low doses. The estimate of the risk of cancer resulting from the low levels of exposure, likely at a university or medical center, are extrapolated from the obvious effects of high doses and dose rates to the low doses/rates on campus. Generally, for radiation protection purposes, these estimates are made using a linear-no threshold model (curve l in Figure 1).  

FIGURE 1 - DOSE RESPONSE MODELS

Explanations of the risks are as follows:

Cancer Fatalities: Of 10,000 people, 2,300 will succumb to some form of cancer. If 10,000 radiation workers are each irradiated with 1 rem of whole body radiation, it is estimated that the radiation may cause four additional cancer deaths in the group.

Genetic Effects: The current incidence of spontaneous mutations ranging from very mild to very serious is approximately 1,000 incidents per 10,000 live births. A dose of 1 rem per generation (30 years) results in an increase in the natural or spontaneous mutation rate by about 1%. The doubling dose (the dose required to produce an incidence of mutations equal to the spontaneous rate) was established by the BEIR III Committee to be in the range of 50 to 250 rem. The corresponding estimate of the 1986 UNSCEAR was 100 rad.

Fetal Effects: Radiation doses delivered during pregnancy can cause different effects depending upon the dose and the time during pregnancy at which it is delivered. Doses received during the pre-implantation phase (up to 2 weeks after conception) can result in prenatal death. Deformed organs and limbs may be observed for exposures during weeks 2 to 8, the organogenesis phase. After six weeks, radiation exposure appears to produce stunted growth and possible mental retardation. The peak for mental retardation seems to be from 8 to 15 weeks after conception. An increase in the risk of solid tumors and leukemia during the first 14 years of life may be a consequence of in-utero radiation exposure.

¹American Cancer Society, U.S. Mortality 2000, "Cancer Facts & Figures 2003", www.cancer.org
²NCRP Report #116, "Limitation of Exposure to Ionizing Radiation", National Council on Radiation Protection and Measurements, March 1993
³Hall, Eric J., Radiobiology for the Radiologist, 3rd edition, J.B. Lippincott Company, 1988

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