Dose-Rate Dependence of High-Dose Health Effects in Humans from Photon Radiation with Application to Radiological Terrorism
D.J. Strom (Pacific Northwest National Laboratory)
After a radiological or nuclear terrorist events or reactor accidents, radiation dose rates are likely to be low in the sense that many hours, or days, or weeks will pass before most people could receive a lethal dose of radiation. This presentation examines how dose rate affects repair and human tolerance for high doses of radiation, what mathematical relationships there are between tolerance dose and dose rate, what the human experience is with high doses at low dose rates, and what protective measures can be taken to exploit repair during low-dose-rate, high dose exposures. In 1981 Lushbaugh, Hübner, and Fry examined human "radiation tolerance" as a function of dose rate. They studied 1) lethal dose that will kill 50% of people within 60 days of exposure without medical care (LD50/60); severe bone marrow damage in 2) healthy men and 3) leukemia patients; 4) temporary sterility; 5) reduced male fertility; and 6) late effects such as cancer. Their analysis was grounded in extensive clinical experience and anchored to a few selected data points, and based on J.L. Bateman's dose-rate dependence theory. This work derives the parameters needed in Bateman's equation for each health endpoint and plots them in a more understandable manner, showing quantitatively how humans can tolerate more radiation lower dose rates. The LD50/60 increases from 3 Gy at high dose rates to >10 Gy at much lower dose rates over periods of several months. The case of an individual who survived for at least 19 y after receiving 9 to 17 Gy over 106 days shows an LD50/60 that increases with decreasing dose rate. This work shows the importance of sheltering when confronted with continuous exposure to radiological contamination such as would be expected from a radiological dispersion event, reactor accident, or ground-level nuclear explosion. *Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy under Contract No. DE-AC06-76RLO 1830.