Radionuclide production Flashcards
Elute/eluting/elution
- process of removing the daughter product from the parent
- aka:milking
Eluant
- Solution used to allow elution to take place
- 0.9% NaCl
Eluate
- Final product of elution
- 99m-Tc04 pertechnetate
Radiolysis
Dissociation of molecules due to radiation
Carrier free
- Radioisotope in pure form
- free dilution by stable isotopes
Radionuclide generators consists of
- a longer-lived parent that decays into the shorter-lived daughter radionuclide
- paret and daughter are not isotopes, therefore, chemical separation is possible
- provides fresh supply of the daughter radionuclide until parent activity is depleted
How long does it take for a 99-Mo - 99m-Tc generator to decay and deplete
2 weeks
What are canadian generator suppliers
- Covidien
- Lantheus
- Mallinckrodt
Describe the ideal generator
- Inexpensive
- Simple, convenient, and quick to set up
- Produces a high yield of the daughter radionuclide, repeatedly and reproducibly
- Properly shielded to ensure minimal radiatioin exposure to personnel
- sturdy and compact for shipping
- eluate should not contain parent radionuclide or absorbent material from column
- should not contain any other contaminants
- daughter radionuclide should have a short effective half-life to minimize patient radiation expose
What is the principle of a generator?
- Constructed on principle of decay-growth relationship
- long-lived parent and short-lived daughter
- different chemical properties allows separation
- not isotopes (daughter has a different z #)
- parent decays to daughter
- daughter is chemically separated
Describe generator yield/activity
- 99m-Tc rapidly builds up following elution
- highest yield when milked every 24 hours
- possible to milk before 24 hours
- sacrifices yield
- 50% of max at 4.5 hours
- 75% of max at 8.5 hours
describe the 99-Mo/99m-Tc generator
- The 99-Mo used for genrators is obtained by either:
fission (n,f) of 235-Uranium - fission moly
- curent method of 99-Mo production
- higher specific activity
Neutron activation (n,y) of stable 98-Mo - lower specific activity
- not used anymore
Describe the solid column
solid column
- glass or plastic column filled with:
- cation or anion exchange resin
- alumina
- zirconia
- parent absorbed to column
- daughter grows because of the decay of the parent
- generator column is a cylindrical container containing alumina powder (Al3, O3)
- rubber stoppers at both ends of the column
- contains wool inside of glass or plastic for shock absorption
- contains glass beads or dispersion of saline
- alumina is washed in pH 5 saline (slightly acidic), acquires a positive charge, which helps absorb the molybdate ions and then loaded into the glass column
- Amount of alumina used in a column depends on the total activity of 99-Mo (5-10g)
- 99-Mo is adjusted to an acidic pH and forms various anionic species
- 99-Mo is absorbed on the alumina column
- column is washed with isotonic saline to remove any undesirable activity
Describe generator production
- the generator is aassembled under aseptic conditions
- tubing is attached to each end of the column to allow fot he elution of the radioactivity and is placed into lead shielding
- membrane filter is located on the elution end of the column
- product passes through during each elution tto ensure its sterility
- the entire generator is autoclaved to ensure it is sterile
List the tests performed before the generator is released for use
- Generator efficiency
- eluate volume
- radionuclidic purity
- radiochemical purity
- aluminum concentration in eluate
- pH of eluate
- pyrogen and sterility testing
Describe radioactive equilibrium
- Generator classified based on: half-life of parent and half-life of the daughter
- 2 most common forms of equilibrium are: secular equilibrium and transient equilibrium
Describe secular equilibrium
- occurs when parent nuclides half-life is significantly longer (~1000 times greater) than the daughter nuclides half life
- due to parent having a considerably longer half-life it will not decay within several daughters half-lifes
- initially the dauhter production>daughter decay
- this relationship allows the daughter activity accumulate
- secular equilibrium is established when the rate of the daughter production appears to be equal to the rate of parent decay
- Parent activity=daughter activity
- after secular equilibrium, the daughter appears to decay at the same half-life of the parent
Explain transient equilibruim
- Occurs when the parent and his daughter half-life differ by a factor of 10-50
- 99-Mo (66 hrs) to 99m-Tc (6.02 hrs)
- half-life will differ by a factor of 11
- as the daughter is produced it will accumulate eventually reaching a maximum activity
- when maximum activity of the daughter is reached the:
- rate of daughter production=rate of daughter decay
- after reaching max activity a state of transient equilibrium can be reached
Transient equilibrium is established when…
- the ratio of parent activity is constant
- After equlibrium is established the daughter will appear to decay at the same rate as the parent until the daughter activity is removed from the generator
Describe the properties of a 99-Mo to 99m-Tc generator
- Consists of 99-Mo parent, which decays to 99m-Tc daughter radionuclide
- Parent properties: 99-Mo
- Reactor produced
- 66 hour half-life
- not ideal for imaging
- long half life, beta emission
- decays by 3 main beta emissions
Describe 99-Mo
- Located on the generator column,binds to alumina
- 66 hour half life
- decay by beta emission
- 86% decays to 99m-Tc
- 14% decays to 99-Tc
- Photons of 740 keV and 780 keV
Describe Metastable technetium
- Remove from column upon elution of the generator
- half-life of 6.02 hours
- decays by isomeric trasition
- ground state is 99-Tc
- Gamma photons of 140 keV
Describe stable technetium
- Radionuclidic impurity
- Half-life of 2.1x105 years
- Decays by beta emission
- stable 99-Ru
- beta emission with Emax= 293 keV
- Generator column storage
How does a generator work?
- 99-Mo is absorbed onto alumina (Al2O3)
- Chemical form of MoO2 -4 molybdate
- 0.22um filter used to ensure sterility of eluate
- generator column shielded with lead or depleted uranium for radiation protection
- The 99-Mo on the column decays to the 99m-Tc
- 0.9% saline is used to milk the generator
- The 99-Mo remains firmly attached to the column but the 99m-Tc (in the form of the pertechnetate ion) is easily detached by the chloride anion (Cl-)
- The 99m-Tc is eluted as sodium pertechnetate
- After an elution, the 99m-Tc activity on the column grows again annd can be re-milked/eluted
- the amount of activity obtained off the generator depends on the amount of time that has passed since the previous elution
- Decay relationship between 99-Mo and 99m-Tc
Describe evacuated vials
- Also referred to as collecting vials
- sterile vacuum vials that come in various sizes
- Made of glass and range in size from 5-30ml
- calibrated to withdraw a predetermined volume based on size
- place vial inside lead pot prior to eluting the generator
Describe eluant vials
- Also referred to as a saline charge
- glass vials that contain a specific volume of 0.9% saline usedto elute
- for a ‘wet’ system the vialwill contain a large volume of saline for continuous use 100-500ml
- for a ‘dry’ system the vial contains a calibrated volume for one time used only 5 to 10 ml
Describe dry generator systems
- 5-20ml saline vial placed on port before attaching the evacuated vial
- 30ml evacuated vial draws the saline through the generator to remove the 99m-Tc activity
- vacuum pulls the saline through the column and into the evacuated vial
- leave the empty saline vial on the entry port until your next elution, to maintain sterility
- place the bacteriostat vial on the collection port to maintainsterility (provided by manufacturer)
- Less chance of radiolysis (formation of hydrogen peroxide and per hydroxyl free radicals
- Oxidants that if present in pertechnetate interfere with normal chemistry
Describe wet generator systems
- Large reservoir of saline connected to generator, which keeps the column continuously bathed in saline
- elution sameas dry generator
- at the end of the elution, generator columne remains bathed in. saline
- very safe, no risk for leaking activity
- saline tubing may freeze
Describe radiolysis in wet generator systems
- due to the column being continuously bathed in saline, the radiation can cause the radiolysis of water
- results in the formation of hydrogen peroxide (H2O2) and perhydroxyl free radical (HO2)
- The oxidants which caninterfere with the 99m-Tc chnaging its oxidation state; cause it to bind more firmly to the alumina
- some manufacturers add disolved oxygen to the saline to elute the wet generato to counteract radiolysis
- Tends to occur with high activity wet generators
- saline in the tubing could freeze during the shipping of the generator
Describe radiolysis of dry generator systems
- Adds oxygen to the column which prmotes the oxidation to the pertechnetate state
Explain troubleshooting of generator systems
empty evacuated vial following elution
- loss of vacuum from vial is the most common cause
- ideally should see bubbles in your saliine vial
- re elute
- if second elution doesnt resolve problem, check the elutionneedle
Increased volume: decreased activity
- Elution vial may have been removedly on previous milking
Accurate volume: decreased activity
- Radiolysis
- re-elue 1-2 hours
