Calculating hematopoietic-mode-lethality risk avoidance associated with radionuclide decorporation countermeasures related to a radiological terrorism incident

Abstract

This paper provides theoretical health-risk-assessment tools that are designed to facilitate planning for and managing radiological terrorism incidents that involve ingestion exposure to bone-seeking radionuclides (e.g., radiostrontium nuclides). The focus is on evaluating lethality risk avoidance (RAV; i.e., the decrease in risk) that is associated with radionuclide decorporation countermeasures employed to remove ingested bone-seeking beta and/or gamma-emitting radionuclides from the body. To illustrate the application of tools presented, hypothetical radiostrontium decorporation scenarios were considered that involved evaluating the hematopoietic-mode-lethality RAV. For evaluating the efficacy of specific decorporation countermeasures, the lethality risk avoidance proportion (RAP; which is the RAV divided by the total lethality risk in the absence of protective countermeasures) is introduced. The lethality RAP is expected to be a useful tool for designing optimal radionuclide decorporation schemes and for identifying green, yellow and red dose-rate zones. For the green zone, essentially all of the lethality risk is expected to be avoided (RAP = 1) as a consequence of the radionuclide decorporation scheme used. For the yellow zone, some but not all of the lethality risk is expected to be avoided. For the red zone, none of the lethality risk (which equals 1) is expected to be avoided.

Keywords: Risk; countermeasures; lethality; radiation; radionuclide.

FIGURE 1

Predicted median lethal dose (D₅₀(y)) for the hematopoietic mode of death for different mammals (rats [Sprague-Dawley], mice [white, non-inbred], dogs, swine, goats, sheep, and humans) as a function of the external low-LET radiation dose rate y to bone marrow in Gy/h. For each species, D₅₀(y) is predicted to approach an asymptotic value > 1.5 Gy (1,500 mGy) as dose rate becomes large (Ainsworth Phenomenon). Dose rate is presented as a categorical variable and is not aligned to tick marks.

FIGURE 2

Central estimates of the asymptotic normalized dose X_∞{A} for the hematopoietic mode of death in humans for a single, negative-exponential-decaying, dose-rate pattern of beta and/or gamma radiation to bone marrow of humans. Results are presented for different initial dose rates A and for three effective retention half-times: 50 d (diamonds), 100 d (squares), and for 1000 d (triangles).

FIGURE 3

Central estimates of the temporal pattern of build-up of the normalized dose X{t, A} for the hematopoietic mode of death in humans when radiation dose rate to bone marrow decreases as a single, negative-exponential-decaying pattern over time after intake of a bone-seeking radionuclide that emits beta and/or gamma radiation. Results are presented for an initial dose rate of 0.01 Gy/h and for three effective retention half-times: 50 d (diamonds), 100 d (squares), and for 1000 d (triangles).

FIGURE 4

Central estimate of the hematopoietic mode lethality RAV for young (<16 y) female humans that ingest radiostrontium in a highly soluble form and afterwards receive radionuclide decorporation therapy (hypothetical) at 1 h (diamonds) or 24 h (squares) after intake of the radioactive substance. Evaluations were carried out for DRRF(1 h) = 10 (diamonds) and for DRRF(24 h) = 2 (squares) for a range of initial dose rates to bone marrow when T_1/2 = 16 y. The two curves overlap for initial dose rates <0.001 Gy/h.

FIGURE 5

Central estimates of the hematopoietic mode lethality RAP for young (<16 y) female humans that ingest radiostrontium in a soluble form and afterwards receive radionuclide decorporation therapy (hypothetical) at 1 h (diamonds) or 24 h (squares) after intake of the radioactive substance. Evaluations were carried out for DRRF(1 h) = 10 (diamonds) and for DRRF(24 h) = 2 (squares) for a range of initial dose rates to bone marrow when T_1/2 = 16 y. The two curves overlap for initial dose rates <0.001 Gy/h.