Answer to Question #253 Submitted to "Ask the Experts"

Q

I'm interested in finding out the best instrument to use for a patient survey following the administration of a pure beta emitter of 2.3MeV max energy (avg E = 0.33Emax). This agent is tagged to monoclonal antibodies and used in cancer patients. It's ⁹⁰Sr or ⁹⁰Y--any ideas here? A determination is required that documents that the patient does not represent a hazard to family or members of the general public following release post administration.

A

One can use a calibrated ionization chamber (such as a portable "cutie pie") which provides an energy-independent measure of dose rate for estimating dose and dose rate at one meter from the patient. In the United States, the Nuclear Regulatory Commission has revised its Part 35 (10 CFR) regulations for the release of patients after an infusion of radioactive material in therapy situations. The objective of the new regulations is to limit the dose rate to any other member of the public to 5 mSv (500 mrem) from radiation emitted by activity in the patient. Zanzonico, Binkert, and Goldsmith (J. Nuc. Med. 40:1024-1028; 1999) have shown that radionuclide therapy with even large amounts (for example, more than 200 mCi) of pure beta-emitters such as Y-90 does not require medical confinement of patients because the dose rates outside the patient from brehmsstrahlung will not exceed the NRC limits.