Impact of Therapy on Dosimetry

DOE-STD-1121-98

Report 65 (NCRP 1980), IAEA Safety Series No. 47 (IAEA 1978b), the Radiological Health Handbook

(Bureau of Radiological Health 1970), and the Health Physics and Radiological Health Handbook

(Shleien 1992).

Therapeutic actions to reduce internal dose following the intake of radioactive material typically

require medical administration of an agent to block, chelate, dilute, or purge the body of the radioactivity.

Blocking agents are used to prevent gastrointestinal absorption through ion exchange processes (e.g.,

Prussian blue for cesium blockage) or adsorption (e.g., antacids or alginates for strontium). These may be

coupled with stomach lavage, emetics, and purgatives or laxatives to accelerate removal or passage

through the GI tract. Chelating agents, e.g., DTPA for plutonium or americium, are usually administered

by intravenous injection and bind with ionic forms in the blood. They are then rapidly excreted in urine.

Dilution of radioactivity can be accomplished by administering a relatively large dose of the stable form

of the element, thereby reducing the likelihood of retention of the radioactive form (e.g., administration of

stable potassium iodide in response to exposure to 131I). Acceleration of normal metabolism to speed

removal of radioactivity can be effective (e.g., diuretics to accelerate body water turnover to eliminate

tritium). For extreme cases of insoluble particle inhalation, lung lavage may be an effective therapy.

Details concerning the effective methods of treatment and therapy for various radionuclide intakes can be

found in the Guidebook for the Treatment of Accidental Internal Radionuclide Contamination of Workers

edited by Gerber & Thomas (Bhattacharyya et al. 1992), NCRP Report No. 65 (NCRP 1980), IAEA

Safety Series No. 47 (IAEA 1978b), IAEA Technical Report Series No. 184 (IAEA 1978a), and ICRP

Publication 28 (ICRP 1978a). These documents should be immediately available to health physics and

medical personnel.

An additional resource for assisting with the medical management of radiation accidents is the

Radiation Emergency Assistance Center and Training Site (REAC/TS), a service operated for the U.S.

Department of Energy by the Oak Ridge Institute of Science and Education (ORISE). REAC/TS

maintains a 24-hour emergency contact list, which can be reached by phone at (865) 576-3131 from 8 am

to 4:30 pm Eastern Time and at other times, (865) 576-1005 (DOE Oak Ridge Operations Emergency

Operations Center).

Sites with potential for intakes of transuranics should have access to a supply of DTPA and a

physician registered as a co-investigator. DTPA is approved by the U.S. Food and Drug Administration

as an Investigational New Drug (IND) and is available to physicians who are registered as co-

investigators (Goans 1996a, 1996b). As of September 1996, physicians can register as IND co-

investigators by contacting the REAC/TS DTPA program, Patrick Lowry, M.D., Head of Medical

Section, at (865) 576-4049.

10.5 IMPACT OF THERAPY ON DOSIMETRY

Most procedures and computer codes used for routine intake and internal dose assessment are based

on standard ICRP assumptions for the biokinetics of radioactivity in the body. Dose reduction therapy

can have significant impact on the validity of these assumptions. The nature of the impact depends on the

type of therapy and the radionuclide of interest. There is no single rule for evaluating data following dose

reduction therapy. It is imperative that the dosimetrist understand the therapeutic processes involved and

the impact on bioassay measurements. Some examples follow.

The use of diuretics to accelerate body water turnover effectively decreases the biological retention

of tritium. Since tritium body water concentration can be easily measured by urinalysis, the actual

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