Technical Assistance Request, Clarification of 10 CFR 35.50 (b) (1)
See the memorandum from J.E. Glenn to W. E. Cline dated November 12, 1991.
This memo responds to a Region II request for clarification of the performance of dose calibrator consistency checks as described in 10 CFR 35.50 (b) (1). Specifically, "is it appropriate for a licensee to preform this test on the cobalt-57 (Co-57) setting although technetium-99m (Tc-99m) is the most frequently used isotope?"
Medical licensees are required to perform a dose calibrator daily constancy check. 10 CFR 35.50 (b) (1) requires, in part, that a licensee check each dose calibrator for constancy with a dedicated check source at the beginning of each day of use, and that the test be done on a frequently used setting. Based on numerous nuclear medicine inspections in Region II, the most frequently used setting is Tc-99m, and based on the requirements of 10 CFR 35.51 (b) (1), the licensees who use Tc-99m more frequently should perform this test on the Tc-99m setting with a dedicated sealed source (which is usually Co-57). However, some licensees perform this test on the Co-57 setting although Tc-99m is the most frequently used setting.
While this issue is not addressed in the Statements of Consideration for either the proposed or final rule on 10 CFR Part 35, effective April 1, 1987, it is believed that the rule is intended to assure that the licensee determines the consistency of the dose calibrator, on each day of use, under the actual conditions of use. Since most medical licensees use Tc-99m for patient dosage administrations more frequently than any other isotope, such licensees must check the Tc-99m setting, on each day of use, with a dedicated check source. If the licensee frequently uses the Tc-99m setting to measure patient dosages but only does a constancy check on the Co-57 setting, it appears appropriate to cite against 10 CFR 35.50 (b) (1) unless the licensee can show that the Co-57 setting is frequently used to measure patient dosages.
It is recommended that Co-57 be used as a standard to measure the constancy of the Tc-99m setting because of the close proximity of its energies. Cobalt-57 has principal energies of 122 and 136 keV and Tc-99m has a principal energy of 140 keV. It is also recommended that dose calibrators having pre-calibrated settings or potentiometers be tested on both the Co-57 and Tc-99m settings because discrepancies or fluctuations have been observed between the two settings when tested for constancy with the same check source. If such discrepancies are observed, it could indicate that there is a problem with one or both of the settings. Inspectors should encourage licensees to do a daily constancy check of all commonly used isotope settings, not only Tc-99m to ensure the accuracy of all administered patient dosages.
Regulatory references: 10 CFR 35.50
Subject codes: 6.4, 6.6
Applicability: Byproduct Materials
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