Dose calibrator QC Flashcards
Why is documentation manditory over 3 years
- Shows compliance
- Trends in QC results
- Shows intermittent problems
Sealed sources
- made of solid epoxy and sealed inside a polyethlene bottle
- leak testing performed annually
Equipment changes are assessed against
- Baseline performance: Relative assessment of values
- Known standards with threshold values
What are common long-lived standards
- 137-Cs: 30 years; 662 keV
- 133-Ba: 10.5 years; 256 keV
- 57- Co: 271 days; 122 keV
- 60- Co: 5.26 years; 1173 keV
what type of radiation detector is a dose calibrator
ionization chamber
What is the function of a dose calibrator
- used to measure the activity of RPs prior to administration
- selector buttons for each isotope
- displayed in curies or bequerels
- the accuracy of patient doses rely on the dose calibrator performance
Accuracy frequency
annual
constancy frequency
daily
linearity frequency
quarterly
geometry frequency
installation and repair
Describe the constancy test
- Ensures a consistent reading daily: Ensures precision and reproducibility over time
- Reference sources: 137-cs, 57-Co (use to assess all isotope settings, and 133-Ba (Use if primary role of DC is used to measure 131-I)
Constancy Result limits
- +/- 5%, if it isnt within limits repair or replace machine
- can be trended on a decay graph
Explain the accuracy test
- To test the instruments ability to measure a source of activity within a stated degree of the true value
- Two NIST reference standards must be used: 57-Co and 137-Cs, one must be 100-500 keV
Accuracy results requirements
Must be within +/- 5% or repairs or replacements must occur
Explain the linearity QC test decay method
Decay method: An activity of Tc measured over various time intervals over 2-3 days
- typically assayed at 6, 12, 24, 48 hours
- continue measurements until activity is under <1110kBq
- % error is calculate
- most accurate, but more inconvienient
- precision with timing is imperitave
Explain the attenuation or cali check linerity QC method
- Series of lead-lined sleeves with varying thickness to simulate decay
- each shield has a df/cf
- needs initial determination of calibration factors
- % error is calculated
- must be performed quickly, under 6 minutes
Describe the geometry QC
- Ensures meausre activity doesnt change with volume or configuration
- Geometry accuracy is affected by position, volume, container shape/size
Geometry QC results
+/- 2%- establish a correction table
Syringe volume and container shape assessment for geometry
- 37-370 MBq/ml 99m-Tc and saline
- Dose in 0.5 ml
- assay
- add increments of 0.5 ml of saline until a total of 2ml
- assay at each increment of saline
Vial volume and container shape assessment
- 37-370 MBq/ml 99m-Tc in 30 ml vial
- assay
- add increments of 2 ml saline until a total 20 ml
- assay at each 2 ml increment
