Answer to Question #1172 Submitted to "Ask the Experts"

Q

What is the Nuclear Regulatory Commission's current requirement for bioassay of individuals involved in the administration of outpatient doses of ¹³¹I in capsule form, in excess of 33 mCi?

A

The current requirements are specified in both the Nuclear Regulatory Commission's (NRC) Part 20 and Part 35 regulations. The more general requirement, in Part 20, specifies that any worker who is likely to receive in a year in excess of 10% of the annual limit on intake (ALI) must be monitored for intake. For ¹³¹I, this would normally be, in effect, a requirement to perform bioassays. The determination of who is to be monitored under this requirement must be made prospectively, that is, at the beginning of the monitoring period (normally the start of the calendar year). The more specific requirement is in Part 35, which requires that, for staff who helped prepare or administer a dosage of ¹³¹I to patients who were hospitalized for compliance with the patient-release criteria, a measurement of thyroid burden must be made within three days of such administration. Although both Part 20 and Part 35 requirements apply, the general rule is that the specific requirement, in this case Part 35, takes precedence over the general requirement. It should be noted that some licensees may have somewhat different requirements incorporated into their licenses. For example, many licensees incorporate the programs described in NRC's Regulatory Guide 10.8 into their licenses. In that case, the requirement is to measure thyroid burden one day after administration of over 30 mCi of ¹³¹I and to consider a measurement two days after administration. In the revised Part 35, which is not yet in effect, the specific requirement in Part 35 is deleted, and the licensee will in that case be expected to comply with the more general, Part 20, requirement.

Sami Sherbini NRC