Radiopharmaceuticals and Radiopharmacy
Radiopharmacy questions test generator operation, kit preparation, quality control, and dose calculation - the daily decisions that determine image quality and patient safety.
Core rules
- Mo-99/Tc-99m generator: Tc-99m is eluted as pertechnetate; Mo-99 breakthrough and aluminum breakthrough must be tested within regulatory and manufacturer limits.
- Kit preparation: follow the manufacturer's instructions for eluate volume, activity, temperature, and incubation time; verify radiochemical purity before administration.
- Common QC includes radiochemical purity by chromatography, aluminum ion breakthrough, pH, and visual inspection for particulates.
- Dose calculation uses decay: A_t = A_0 × e^(−0.693t/T½); Tc-99m half-life is 6.02 h.
Worked example
A vial contains 1,000 MBq of Tc-99m at 08:00. What activity remains at 14:00? Reasoning: elapsed time is 6.0 h, approximately one half-life (6.02 h). A = 1,000 × e^(−0.693×6/6.02) ≈ 500 MBq. If the prescribed dose is 740 MBq at 14:00, this vial cannot supply it; a fresher eluate or higher-calibration vial is required. Calculate before drawing to avoid remeasuring and delaying the patient.
Traps
- Using calibration-time activity instead of administration-time activity.
- Failing to assay the patient dose in a dose calibrator before injection.
- Accepting a kit past expiry or prepared with the wrong eluate volume.
- Reporting a radiochemical purity result without running the specified chromatography system.