Presentation Transcript
DOSE CALIBRATOR :DOSE CALIBRATOR Gas-filled detector
It based on ionization chamber
It assures the user that the amount of radiofarmaceutical administrated is the correct dose for the patient.
Dose Calibrator :Dose Calibrator (NRC) requires licensees to perform quality control test on dose calibrator according to recognized standards of practice.
Retain calibration records for 3 years.
Records must include the model, serial number, date of calibration, results, and name of individual who performed test.
Dose calibrator :Dose calibrator Accuracy
Constancy
Linearity
geometry
Accuracy :Accuracy How close a reading is a true value
It measured with a long-life standards 57Co or 137 Cs
The source must produce gamma emission between 100Kev- 500Kev
Installation and annually
Must produce readings of +/- 10% of expected value.
Accuracy :Accuracy If accuracy error is greater than 10% the dose calibrator must be repaired or replaced.
Constancy :Constancy Precision testing assures the reproducibility of result.
Preferably 137 Cs or 57 Co.
Every day (instrument is used)
average reading of standard (decay standard) is plotted and constancy is measured, a 10% +/- tolerance limit of the decay standard is acceptable.
Constancy :Constancy 137 Cs or 57 Co is measured at each commonly used radionuclide setting. Ex: Tc, I-131, I-123 etc.
Each measurement is compared with expected decay corrected value for the standard at that setting for that day.
Constancy :Constancy If readings consistently fall out of limits greater than 10%, dose calibrator should be taken out of service until problem is fixed or replaced.
Linearity :Linearity It refers to the accuracy of reading over a wide range of activity. From millicuries to microcuries.
Decay and shielding methods. decay is done by using a short half-life isotope (tc99m) and assaying it over several days, comparing predicted, with measured results. Generally starting activity is highest activity administered to a patient.
Starting activity should be assayed until it reaches 30 microcuries
Linearity :Linearity Shielding method (calicheck) is a series of lead tubes that absorb tc99m photons by a known amount.
Measurements of the shielded source simulate radioactive decay.
Saves time and personnel exposure.
Measured activity must be within +/- 10% of expected activities.
Linearity is performed quarterly.
Geometry :Geometry It is performed at installation and after it is repaired.
The testing covers the range of volumes and volume configuration for which it will be used. Ex: 10mci in 1ml vs 10mci in 10ml.
Correction factor when the error exceed 10%
Correction factor should be displayed on dose calibrator