Source of Radioactivity for Dose Monitor Constancy Testing
For constancy testing of dose monitors in nuclear cardiology and radiation therapy settings, sealed radioactive check sources are used, with the specific isotope varying by application—typically long-lived isotopes such as Cesium-137 (137Cs) for therapy dosimetry systems or flood sources containing radioactive material for gamma camera quality control. 1
Quality Control Sources in Nuclear Cardiology
Sealed Source Phantoms for Automated Systems
- Modern SPECT and SPECT/CT systems incorporate built-in automated daily quality control procedures that require placement of a sealed source phantom in the appropriate location, with some systems featuring quality control sources that automatically move into the field of view. 1
- These automated systems perform acquisition and data analysis automatically, yielding pass/fail results for constancy verification. 1
Flood Sources for Conventional Gamma Cameras
- Daily performance assessments of gamma cameras require obtaining uniform flood fields using radioactive flood sources to verify uniform detector responsiveness over the imaging field. 1
- Weekly high-count flood acquisitions are performed using these same flood sources to assess spatial resolution and field uniformity. 1
- For SPECT cameras using translating radioactive rod sources for attenuation correction, daily low-count floods and weekly high-count floods are required using these rod sources. 1
Common Pitfall
Personnel exposure occurs during manipulation of flood sources or phantoms for camera quality control assessment, making proper handling technique and time/distance principles essential. 1
Radiation Therapy Dosimetry Check Sources
Long-Lived Isotope Standards
- Radioactive check sources are specifically recommended for operational and constancy checks of dosimetry systems used for calibration of therapeutic x-ray generators, including linear accelerators. 2
- Cesium-137 (137Cs) gamma-ray sources serve as calibration standards for radiation therapy dosimetry, having been proposed as substitutes for radium in treatment applications and requiring suitable calibration for consistency. 3
Calibration Intervals
- When a check source is used consistently with stable results, the interval between formal calibrations at Accredited Dosimetry Calibration Laboratories can be lengthened beyond the standard 2-year interval. 2
- A formal protocol using a segregated source for quality control trending and recalibration of operational sources minimizes error propagation during recalibration. 4
Key Operational Considerations
Source Selection Criteria
- The radioactive source must have a sufficiently long half-life to provide stable reference readings over extended periods without frequent decay corrections. 2, 4
- Sources must be sealed to prevent contamination and allow safe handling during routine quality control procedures. 1