Comparison of intake and committed dose equivalent permitted by radiation protection systems based on annual dose equivalent and committed dose equivalent for a nuclide of intermediate effective half-life.

Comparison of the 226Ra ingestion permitted by a radiation protection system that limits dose equivalent, with that permitted by the ICRP system and by the ICRP system modified through the use of the Norris retention function in place of the ICRP alkaline earth model, shows that the total ingested activity and the total committed dose equivalent to bone-surface tissues are approximately the same under the three protection systems when exposure occurs at the maximum permissible level for 50 y. Under the dose-equivalent-limitation system, annual ingestion decreases from 451 kBq during the first year to 36 kBq during the fiftieth year. The total ingestion equals 3.45 MBq. Annual committed dose equivalent decreases from 3.6 Sv during the first year to 0.3 Sv during the fiftieth year. The total committed dose equivalent equals 27 Sv. Under the ICRP system and its modified version, the annual limits on intake are constant with time at 70 kBq and 63 kBq, respectively. The total intakes are 3.50 MBq and 3.15 MBq. The annual committed dose equivalent is also constant with time at 0.5 Sv for both versions. The total committed dose equivalent is 25 Sv. These results suggest that a pure dose equivalent limitation system similar to that which has evolved at U.S. defense-related facilities permits lifetime exposures similar to those permitted by a committed dose limitation system for radionuclides of intermediate effective half-life. Lifetime cancer risk for the maximally-exposed individual may be greater under the dose equivalent-limitation system due to the more rapid increase in committed dose equivalent which occurs with time compared to the increase under the ICRP system or its modified version.