QUALITY CONTROL OF RADIOISOTOPE DOSE CALIBRATORS

TEST REQUIRED......................FREQUENCY ..........................................REGULATORY AGENCY

ACCURACY ..................................ANNUALLY .....................................NRC/STATE DEPT OF NUCLEAR SAFETY

CONSTANCY ...............................DAILY .................................................NRC/STATE DEPT OF NUCLEAR SAFETY

LINEARITY ....................................QUARTERLY ..................................NRC/STATE DEPT OF NUCLEAR SAFETY

GEOMETRY ...................................INSTALLATION ..........................NRC/STATE DEPT OF NUCLEAR SAFETY

GEOMETRY TEST MUST ALSO BE PERFORMED AFTER REPAIR, RECALIBRATION OR AFTER MOVING INSTRUMENT

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ACCURACY TEST: This test is designed to show that the calibrator is giving correct readings throughout the entire energy scale that we are likely to encounter. Low, medium, and high energy standards (usually Co-57, Ba-133 or Cs-137, and Co-60, respectively), are measured in the dose calibrator using appropriate settings. Standard and measured values are compared.

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CONSTANCY TEST: This test measures precision and is designed to show that, using a long-lived source, usually 30 y Cs-137, reproducible readings are obtained day after day on all the various isotope settings we are likely to use. The long-lived source is placed in the dose calibrator. Activity is then measured on the Cs-137 setting and all other routinely used settings on a daily basis. Values are recorded in the appropriate logbook and are compared with recent values to determine if instrument is maintaining constancy on a day-to-day basis.

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LINEARITY TEST: This test is designed to prove that the dose calibrator readout is linear for sources varying from the µCi range through the mCi range. A high activity Tc-99m source (50-300 mCi) is measured at T₀ and at predetermined time intervals up to 48 hours. Expected and actual measurements are compared (and may be analyzed graphically) to determine if the instrument is linear throughout the activity range we are likely to encounter.

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GEOMETRY TEST: This test is designed to show that correct readings can be obtained regardless of the sample size or geometry. One ml of Tc-99m in a 10 ml syringe (activity 25 mCi) is measured in the dose calibrator and the value obtained is recorded. The activity is then diluted with water to 2 ml, 3 ml, 5 ml, and 10 ml. At each of these points a reading is taken and the value recorded. Data are then evaluated to determine the effect of sample geometry on the dose calibrator reading. If instrument is geometry-dependent, it may be necessary to routinely correct readings obtained when using calibrator.

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SPECIFICATIONS FOR ALL DOSE CALIBRATOR QC TESTS

1. Deviation from standard or expected values must be within +/- 10%.

2. If Deviation >10%, then obligation is to record value, note repair or recalibration of instrument, retest, and record new values. Every dose must be mathematically corrected until the instrument is repaired. There is NO LONGER a reporting requirement.

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FULL-WIDTH HALF-MAXIMUM VALUE

Determines ability of a sodium iodide (thallium) or solid state crystal to resolve gamma ray energies. Measures only resolution, not sensitivity.

For NaI(Tl), Normal Value is 6-10%

for Ge(Li) Crystal, typical value is <1% across entire energy spectrum.