Radiopharmacy and Radiopharmaceutical Quality Control
What the exam tests
Radiopharmacy items test generator operation, purity definitions, kit preparation, and release limits. You must distinguish radionuclidic, radiochemical, chemical, and biological purity, and calculate radiochemical purity from strip results.
Core rules
- A Mo-99/Tc-99m generator produces Tc-99m (6 h half-life) from Mo-99 (66 h). Yield depends on time since last elution; eluting too soon gives a low Tc-99m yield.
- Radionuclidic purity limits Mo-99 breakthrough, commonly 0.15 kBq Mo-99 per MBq Tc-99m; assay each eluate with a dose calibrator or gamma spectroscopy.
- Chemical purity includes aluminum breakthrough, commonly ≤10 μg/mL; aluminum can alter tagging and biodistribution.
- Radiochemical purity (RCP) is the fraction of activity in the desired chemical form. Measure by validated chromatography; impurities include free pertechnetate and hydrolyzed-reduced technetium.
- Kits must be stored, reconstituted, and used per labeling; check expiration, particle size for MAA, sterility, and endotoxin.
Worked example
An ITLC assay of a Tc-99m MDP preparation shows 3% activity at the free-pertechnetate position and 2% at the origin (hydrolyzed Tc). RCP = 100% − 3% − 2% = 95%. If the product limit is ≥90%, it passes; if the limit is ≥95%, it is borderline and should be investigated before injection. The reasoning matters more than the arithmetic: identify what each strip position represents before subtracting.
Traps that cost marks
- Confusing Mo-99 breakthrough (radionuclidic purity) with free pertechnetate (radiochemical purity).
- Testing an eluate before it has cooled or using the wrong geometry in the dose calibrator.
- Injecting a kit after its expiry or after signs of clumping (especially MAA).
- Recording a purity result without the strip system, solvent, and cutoff used.