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.

Calculating Pulmonary-Mode-Lethality Risk Avoidance Associated with Radionuclide Decorporation Countermeasures Related to a Radiological Terrorism Incident

“…Evaluating Pulmonary Mode Lethality RAV and RAP Lethality risks are evaluated based on the HF model (Scott 2004) using the approach described in the cited related paper (Scott 2009). For the HF model and for the pulmonary mode of death, the risk function R (i.e., individual probability of radiation-induced lethal damage to the lung) is given as a function of lethality-mode-specific hazard, H pul (a cumulative hazard function for the pulmonary mode) and survival probability, S, by (Scott and Hahn 1989):…”

“…For example, the normalized dose increment that occurs before applying lung lavage can be evaluated and added to the additional normalized dose increment that occurs after application of the procedure. Risk is then evaluated based on the sum of the two normalized dose increments (Scott 2009). Evaluating the normalized dose X requires a functional relationship between D 50 and the organ-specific radiation absorbed dose rate y when held at a given value.…”

“…The following analytical solution applies for a single negative-exponential-decaying dose-rate pattern with initial dose rate A and decay parameter λ (Scott and Dillehay 1990;Scott 2009):…”

“…However, the focus here is on scenarios involving inhalation of highly insoluble aerosols that mainly irradiate the respiratory tract. A related paper addresses ingestion (via a liquid) of highly soluble forms of beta and/or gamma-emitting radionuclides that deposit in the skeleton and irradiate the radiosensitive bone marrow (Scott 2009). …”

“…The related paper (Scott 2009) introduces health risk assessment (HRA) tools that facilitate planning for and managing radiological terrorism incidents such as those that involve an RDD. The indicated HRA tools include analytical functions for evaluating the lethality risk avoidance (RAV) due to protective countermeasures and the risk avoidance proportion (RAP) (RAV divided by the lethality risk in the absence of protective countermeasures).…”