Concerning ionizing radiation-induced cancer from internally deposited radionuclides.

Purpose: A comparative evaluation was conducted of ionizing radiation-induced cancer from internally deposited radionuclides.

Materials And Methods: Data were evaluated for humans for (226)Ra, and for laboratory animal studies for alpha-emitters (228)Ra, (226)Ra, (224)Ra, (238)Pu, (239)Pu, (228)Th, (252)Cf, (249)Cf, and (241)Am, and for beta-emitters (90)Sr, (90)Y, (91)Y, and (144)Ce. Intake routes included ingestion, inhalation, and injection.

Results: Cancer risk associated with protracted ionizing radiation exposure is a non-linear function of lifetime average dose rate to the affected tissues. The lifetime effects are best described by three-dimensional average-dose-rate/time/response surfaces that compete with other causes of death during an individual's lifetime. At the higher average dose rates the principal deleterious effects are those associated with radiation-induced injury, while at intermediate average dose rates radiation-induced cancer predominates.

Conclusions: The cumulative radiation dose is neither an accurate nor an appropriate measure of cancer risk associated with protracted ionizing radiation exposure. At low average dose rates the long latency time required for radiation-induced cancer may exceed the natural lifespan yielding a lifespan virtual threshold for radiation-induced cancer for cumulative doses below about 5-10 Sv for bone, bone marrow and lungs.