Neutron rich radionuclides decay via positron and the ones generally used in PET are in the above diagram (there are some additional PET tracers not mentioned)
Regulatory agencies NRC and FDA
NRC use to only regulate by-product materials, but since 9/11 that philosophy has changed
NUREG-1556 - Program - "Specific Guidance About Possession Licenses for Production of Radioactive Material Using an Accelerator.” published October 2007
Volume 21 - "Program-Specific Eventually all State in the US will be required to regulate all radioactive materials." published October 2007
Volume 13 Rev. 1 - “Program-Specific Guidance About Commercial Radiopharmacy Licenses” was published November 2007.
Volume 9 Rev. 2 - “Program-Specific Guidance About Medical Use Licenses” published January 2008
Current market cyclotrons for PET are classified as "Negative Ion"
How do we accelerate negative ions?
Take Hydrogen and add an e- to its orbit (1P:2e-)
Or a deuteron is produced which contains 1P/1N:2e-
Cyclotrons are manufactured at different energy levels
The least amount would be in the range of 8 MeV
Most commercial systems for PET are between 12 - 18 MeV
Some are as high as 30 MeV which is required to produce 124I
FYI - As a general rule linear accelerators usually do not have enough energy to create the β+ needed in PET
The making of FDG
First you need to 18F
18O water is the target, but only 1% is found in our drinking water
It can be refine it to the point where 18O is 97%. The product is then ready for the production of 18F
Another method to produced 18F is to place 14Ne high pressure and then bombard it deuteron
Beam production and the operation of a cyclotron (use mouse over to see the beam - this may not work in Bb, see other site)
Ion Source is the where the negatively charged ions enter the system
As they spins out outward the energy of the negative ions increases
Speed increases with the enhancement of the four Dees, which alternate a charge (polarity) with each dee causing the ion particle to increase in speed in a controlled path which is contained within the magnetic field (see magnet)
This polarity causes the ion to either be attracted or repelled along its path pending its location
Dee's change polarity ~ 3.0 x 106/second
The orbit is not really circular, but angled with the shape of the Dee, as ion is pushed/pulled along with variation in charge
The beam is 6-8 mm beam in diameter, focused, as it increases in energy as it goes "up hill" and coasts in the the valley (look at the Dee structure)
After ~200 cycles, at the edge of the Dees the ions fly off the Dee and head for for a target (note there many - allows for production of other/or same product)
Prior to reaching the target it strikes an extraction foil
This carbon foil is only a few atoms thick
It strips off the electrons leaving just the proton as the proton continues to the target
Note - electrons and protons spin in different directions and when the electrons are stripped off the beam the negatively charged ion becomes positive
Placement of the foil can vary with one or more targets being bombarded
An advantage to the negative ion cyclotron is that does not become radioactive or contaminated therefore making it easier to decommission
Target for producing 18F
The proton beam then head to its target
In front of the target is Helium that is under pressure with a thin foil overing the gas
Foils are referred to as haver foils
On the opposite side is 18O is water under pressure acting as a coolant
In the center is the 18O being bombarded with protons
Adding protons to the mix and producing 18F - 18O (p,n)18F
Every two to three hours the 18F can be extracted, more 18O can be added and the process continues
Usually several thousands of mCi are produced per 2 or so hours
Question - If 15mCi of 18F is calibrated for 10am, how many mCi are there if the dose was extracted from the cyclotron at 4am?