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Radiopharmacy and quality control
A radiopharmaceutical must be as safe as any drug (sterile, pyrogen-free) and radioactively correct (the right isotope, in the right chemical form, in the right amount) — and each condition has its own test.
Why it matters in the exam
The exam separates types of purity. Radionuclidic purity — is a foreign isotope present (Mo-99 breakthrough). Radiochemical purity — what fraction of the activity is in the desired chemical form; tested by chromatography (ITLC), and for most Tc-99m agents at least 90%–95% is usually required. Radiochemical impurities show on the image: free pertechnetate — uptake in the thyroid, stomach and salivary glands; reduced-hydrolysed (colloidal) Tc — uptake in the liver and spleen. Chemical purity — for example aluminium, which may cause flocculation.
Specific activity — activity per unit mass. It is critical for agents that bind receptors or enzymes (peptides such as DOTATATE, brain ligands, antibodies): a large mass of unlabelled compound competes for receptors, lowers uptake and may cause a pharmacological effect. For agents taken up by a high-capacity process (FDG, MDP) it is less critical. FDG synthesis is usually by automated nucleophilic substitution in a closed module; the older electrophilic method has lower yield and specific activity.
Preparation: a preparation room with classified filtered air, and shielded workstations (hot cells or isolators) held at negative pressure relative to the room so radioactive air does not escape, while clean air is kept around the product. Written standard operating procedures (SOP) ensure uniform work, training and documentation. Dose calibrator: daily constancy with a long-lived source (for example Cs-137); annual accuracy with certified sources; periodic linearity by following the decay of a Tc-99m source or with shielding sleeves; geometry at installation. Every dose is measured before administration.
Key points
- Radionuclidic, radiochemical and chemical purity are three different tests.
- Free pertechnetate — thyroid, stomach, salivary; colloid — liver and spleen.
- Specific activity is critical for receptor agents.
- Dose calibrator: daily constancy, annual accuracy, periodic linearity.
- Written procedures and documentation for every preparation.
Summary table
| Test | What it checks | Method or frequency | Image sign when it fails |
|---|---|---|---|
| Radionuclidic purity | A foreign isotope | Mo-99 breakthrough at each elution | Unnecessary radiation |
| Radiochemical purity | The chemical form | ITLC | Free pertechnetate — thyroid and stomach; colloid — liver |
| Specific activity | Activity per unit mass | Product-specific | Low uptake for receptor agents |
| Dose calibrator constancy | Measurement stability | Daily, Cs-137 | Wrong doses |
| Dose calibrator linearity | Accuracy across the activity range | Periodic, decay or sleeves | Error at high activity |
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Sources
- EANM Guidelines on Current Good Radiopharmacy Practice (cGRPP) for the Small-Scale Preparation of Radiopharmaceuticals, 2021 — Quality control, premises and documentation
- European Pharmacopoeia: Radiopharmaceutical Preparations General Monograph, current edition — Radiochemical purity and specific activity
- AAPM Report: The Selection, Use, Calibration and Quality Assurance of Radionuclide Calibrators, 2012 — Constancy, accuracy, linearity and geometry
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.