Answer to Question #3745 Submitted to "Ask the Experts"

1. Where did the Nuclear Regulatory Commission standard for MBT (molybdenum breakthrough) come from?

2. What was the reason for the reduction of the standard from 1 microcurie per milicurie to 0.15 microcuries of ⁹⁹Mo per millicurie of ^99mTc?

1. The standard was based on a consideration of the detection capability of dose calibrators, the need to ensure consistency of elutions from the resin column, and the prudency of establishing and maintaining an upper bound on the molybdenum breakthrough. These considerations help avoid unnecessary radiation exposure to the patient.

2. The current MBT requirement dates back to at least 16 October 1986 (51 FR 36967). At that time, 10 CFR 30.34(g) was revised to change the generator elution requirement to a requirement that licensees preparing ^99mTc radiopharmaceuticals could only use ^99mTc that contains less than 0.15 microcuries of ⁹⁹Mo per millicurie of ^99mTc. The licensee was required to perform the test and retain records in accordance with 10 CFR 35.204. Part 35 currently requires that MBT be determined only for the first elution of a particular generator. The MBT numerical criterion has been constant for at least 18 years.

Thomas Essig, CHP