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
When is transient equilibrium reached for Mo/Tc?
After 24 hours.
It is most efficient to extract the 99mTc in a 24 hour cycle
