U.S. Nuclear Regulatory Commission

Technical Assistance Request, Clarification of 10 CFR 35.50 (b) (1)

HPPOS-280 PDR-9306150132

Title: 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