Dose Calibrator Instrumentation

Subgroup IV: Instrument Operations and Quality Control

What tests are run on a dose calibrator?

constancy, accuracy, linearity, geometry

How often is constancy run on a dose calibrator?

daily

How often is linearity run on a dose calibrator?

quarterly

How often is accuracy run on a dose calibrator?

annually

How often is geometry run on a dose calibrator?

installation and after repair/movement

dose calibrator constancy definition

today’s readings fall within an acceptable range compared to prior readings

sources used for dose calibrator constancy

Co-57, Ba-133, Cs-137

dose calibrator constancy acceptable results

±10%

What action should you take if the dose calibrator constancy is out of range?

if consistent, explore sources of error; consider repair or replacement

dose calibrator accuracy purpose

does the dose calibrator accurately measure the amount of activity of the radioactive material placed in the chamber

What sources can be used for dose calibrator accuracy?

Co-57, Ba-133, Cs-137 (must be NIST-traceable)

dose calibrator accuracy procedure

• need at least two reference sources of different gamma ray energies

• decay-correct each source from the date of calibration to the date of the test

• measure each source three times, take the average reading

• express the results as % error relative to the expected activity

dose calibrator accuracy acceptable results

±10%

What actions should you take if the dose calibrator accuracy falls outside of the acceptable range?

repair or replace

dose calibrator linearity purpose

verify that the dose calibrator responds to varying activities in a linear fashion

What activity range should be tested for a dose calibrator linearity test?

highest amount of activity ever present in department (~50-100 mCi in a hospital) down to 30 uCi

What source is used for a dose calibrator linearity test?

Tc99m

dose calibrator linearity procedure methods

• multi-day decay method, 30 hour reading is the standard

• Calicheck or Lineator method (sleeve method)

dose calibrator linearity acceptable results

±10%

What actions should you take if the dose calibrator linearity falls outside of the acceptable range?

if deviation from expected values is seen in a particular range, use a correction factor for that range

dose calibrator geometry purpose

calculate a correction factor to correct for the dose calibrator’s dependence on sample geometry

What source is used for dose calibrator geometry?

Tc99m

dose calibrator geometry procedure

• 25 mCi in 0.5 mL in each container type, take reading

• repeat with 1 mL, 2 mL, 3 mL, 4 mL, 5mL

• middle volume reading is standard (3 mL for a 5 mL syringe)

• calculate a correction factor

dose calibrator geometry correction factor formula

CF = (activity at any volume) / (activity at 3 mL)

dose calibrator geometry acceptable results

±10%

What actions should you take if the dose calibrator geometry falls outside of the acceptable range?

determine a correction factor that can be applied to a particular radionuclide or measurement situation that comes up frequently

Given the following data, does this dose calibrator pass the linearity test?

yes

Given the following data, does this dose calibrator pass the linearity test?

no

Given the following data, does this dose calibrator pass the geometry test?

yes