Radiopharmacy Flashcards
What is radiopharmacy?
Involves preparation of radioactive materials for patient administration that will be used to diagnose and treat specific diseases in nuclear medicine.
What are the roles of a radiopharmacist?
Activities/responsibilities:
Formulation and stability of radiopharmaceuticals (RPs).
Managing the production of RPs.
Health and safety for individuals dealing with RPs
Clinical role:
Give advice on use of RPs.
Give input to patient care.
What is alpha decay?
A type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms or decays into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two.
What is beta decay?
A type of radioactive decay in which a beta particle is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide.
What factors should be considered when radiopharmacy is carried out?
Location: near Nuclear Medicine Department
Layout: smooth orderly flow of work - separate rooms for separate purposes.
Budget: building costs, equipment, running costs, maintenance costs.
Either (for a centralised facility):
Full suite of rooms - clean room facilities - contained workstation.
Or (local operation):
Isolator - small workloads.
RPs are sterile products, so must be in a sterile area e.g. at positive pressure. But, production area should be at negative pressure relative to the outside world.
What working practices should be followed?
Appropriate shielding - lead, tungsten, aluminium, perspex.
Protective clothing / gloves.
Contained workstation.
Tray with absorbent tissue.
Non-absorbent surfaces.
Eating, drinking etc forbidden.
Frequent monitoring.
Use of fume cupboards for gaseous or volatile materials.
What are radiopharmaceuticals?
These are medicinal products which are radioactive.
Radiopharmaceuticals may consist of various chemical forms, contained in a variety of dosage forms.
A radiopharmaceutical is made by reacting the radionuclide with various ligands.
What are the advantages of the radionuclide (Technetium-99m)?
Ideal physical properties for imaging (140keV).
Decays by pure gamma radiation.
Technetium-99m decay to Tc rapid (short half-life, 6hrs).
Versatile coordination chemistry (forms complexes easily).
What is the mechanism of radiolabelling?
Incorporation of a radionuclide into a molecule:
Commonest method; join a radionuclide with a compound with desired biological properties, usually by covalent bonding (eg 99mTc labelled RPs, blood cells labelled with Tc, Cr or In).
Bifunctional chelates:
Used for proteins/peptides.
A complex is formed between protein & a chelate, which is then labelled with radionuclide.
Isotope exchange reactions:
When compound of interest has an element which has a radioactive isotope – so replace a proportion of atoms with this isotope. Used to label with 14C, 32S, 3H, iodine
Why is technetium-99m used for radiolabelling?
One reason that Tc is widely used is its diverse chemistry; it can exist in oxidation states from -1 to +7 (has 7 electrons in outer shells available for bonding).
However, Tc in the various possible reduced states (+1, +3, +5) is relatively reactive, will readily bond to ligands, chelating agents.
To lower the oxidation state of the Tc atom, (which can then bind to ligands) – a reducing agent is added (to reduce oxidation state of Tc).
The most common means of achieving this is by adding a stannous (tin) salt.
Wide variety of bonding possibilities using all the reduced states of Tc – hence the popularity.
How are cold kits prepared?
Radioactive concentration of generator eluate is calculated, then appropriate volume of eluate is added to ‘cold kit’ using a syringe.
Invert several times to mix.
Incubate according to instruction for a few minutes (room temperature, or may require heat).
Individual doses are taken from the stock for named patients – syringe plus suitable shielding are sent for immediate administration.
Each patient activity must be measured and recorded in the radiopharmacy log.
How can quality assurance of radiopharmaceuticals be carried out?
Documentation: Guide to GMP – logs for receipt of materials, elution of generator. SOPs for preparation and supply of RPs. Tests on equipment, environment, radiation safety.
Operator technique: broth transfer tests every 3 months.
Equipment: regular checks on calibrators etc.
Environment: contamination - particulate, microbial. Radioactive contamination of surfaces. Overpressures in sterile suite. Air flow rates, efficiency of filters.
What tests should be carried out on the final product?
Radioactivity. Radionuclide identity. Radionuclide purity. Radiochemical purity. Chemical purity. Foreign particulate matter (use polarised light). Particle size. Sterility. Pyrogens.
What are the different ways localisation occurs?
Physical - aggregates can get trapped in capillaries (eg in lung, pulmonary embolism).
Chemical - certain RPs are hydrophilic, localise in kidney.
Biological - receptor imaging agents or antibodies bind to receptors or tumour-associated antigens.
What are the methods of localisation?
Capillary trapping. Ion-exchange. Aerosol deposition. Transport mechanisms. Phagocytosis and pinocytosis. Metabolic incorporation. Autologous products. Immunological mechanisms.
