Radiopharmacy production Flashcards
Give an example of a long half-life radionuclide
Iodine-131
* delivered in ready-to-use form (tablet)
* half-life = 8 days
Why are radionuclide generators needed in the radiopharmacy?
Short half-life radionuclides for diagnostic imaging would have significant decay during transport
What is the basis working principle of the radionuclide generator?
- Long half-life radionuclides decay
- Producing short half-life radionuclides
- Equilibirum is established between the parent and daughter nuclides
- Chemically separate the two (need to be able to do this!)
What is a radionuclide generator?
Device that allows a short-lived daughter radionuclide to be separated and extracted from a longer lived parent radionuclide (that would have been produced using an accelerator or nuclear reactor)
How is 99m-Tc produced from 99-Mo?
- Parent 99-Mo decays via beta minus emission to 99m-Tc
- 99m-Tc is in a metastable state, will decay by gamma ray emission to 99-Tc
How does the 99Mo/99mTc generator work?
- Glass column filled with alumina (Al2O3)
- About 75GBq of 99-Mo is bound to alumina at top of column
- 99-Mo decays to 99m-Tc
- Porous glass disk at bottom of column ensures alumina is retained
- Separation via ion exchange column: saline (milking) solution is passed through the glass column
- Milking solution chemically reacts with any 99m-Tc
- Eluted 99m-Tc is extracted from the generator
How does the Mo/Tc separation work?
- 99Mo is loaded into column as (NH4+)(MoO4-)
- Ion exchange column (washing with saline aka elution)
- MoO4(2-) adsorbed onto aluminium oxide column
- Decays to TcO4- (single charge = less tightly bound)
- Pulling saline through: chloride ions easily exchange with the TcO4- ions (but not the MoO4- ions)
- Eluate contains Na+TcO4- (sodium pertechnetate)
What are the features of the Mo/Tc generator and why?
Physical features
- Tubing: allows column to be washed through with saline
- Inlet: a needle for saline vial can be inserted
- Outlet: needle for empty evauated vial
- Filter: keeps the aluminium oxide within the glass column but removes small particles from the sample (don’t want them in the pertechnetate)
- Lead shielding: operator safety, glass column is only a partial shield, it cannot shield from gamma radiation
- Shielded vials: for collecting the Tc99m product
What is the fundamental principle of the radionuclide generator?
Immediately after the 99m-Tc is extracted, the 99m-Tc radioactivity starts to build up again until it becomes in equilibrium with production from the parent 99-Mo.
How do you calculate the activity (Ad) of the daughter radionuclide?
Bateman equation
Ad = {lambda_d / (lambda_d - lambda_p)} * {Ap(0)} * {exp(-lambdap.t) - exp(-lambdad.t)}
What is transient equilibrium?
When production rate = decay rate.
As the parent decays, the daughter activity will increase to a maximum (transient equilibrium), then effectively decay according to the decay constant of the parent, lambda_p.
Why does transient equilibrium occur in the Mo/Tc radionuclide generator?
This special type of equilibrium can be established because the 99Mo parent T/12 is 67h which is not significantly greater than that of the daughter, 6h
TE occurs when parent half-life is 10x the daughter half-life.
What is the Bateman equation for transient equilibrium?
Bateman equation = activity of daughter
Ad = {lambda_d / (lambda_d - lambda_p)} * {Ap(t)}
What does the activity as a function of time look like for the Mo/Tc radionuclide generator?
- 99Mo decay from initial activity as normal
- 99mTc build up over 24 hours
- If not extracted, 99mTc will decay as normal
- If extracted, sudden drop in activity to zero, then build up again over next 24 hours. Repeat for 5 days (120 hours)
How do you know when transient equilibrium has been reached?
When the activities of the daughter and parent radionuclides are very similar
