Neutron rich radionuclides decay via positron by converting a P+ to a No and then release a β+. It also appears that there is some electron capture occurring, where the P+ captures an inner shell electron, converts to a No, then releases K-characteristics x-rays. When this happens no β+ is produced. Here are some of the percentages of electron capture
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
FDG
PET producers must meet Current Good Manufacturing Practice (CGMP) that complies with CFR 212
PET producers must submit a new drug application (NDA) or abbreviated new drug application (ANDA)
Drug Master File (DMF) - gives detailed information about radiopharmaceutical preparation, packaging, and what the FDG likes
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-). This makes it negative
Or a deuteron is produced which contains 1P/1N:2e-
Cyclotrons are manufactured to produce different energy levels
Lowever energy cyclotrons start off at 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 18O
18O water is the target, but only 1% is found in our drinking water
It can be refined to 97% which is required if you want to production of 18F
Another method to producing 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) where each dee causing the ion particle to increase its speed in a controlled path which is contained by a magnetic field
This polarity causes the ion to either be attracted or repelled along its path pending its location (as it crosses from one Dee to the other)
Dee's change polarity ~ 3.0 x 106/second
The orbit is not really circular, but angled with the shape of the Dee, as the atom 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, the atom is at the edge of the Dees where it fly off the Dee and head for for a target (note - there are multiple takes which allows you to make more than "batch" at a time of the same product or another 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. 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 of a 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 covering the gas
Foils are referred to as Haver foils
On the opposite side of 18O is water under pressure acting as a coolant
In the center is the 18O being bombarded with protons
Adding protons to the mix produces 18F - 18O (p,n)18F
Every two to three hours 18F can be extracted, more 18O can be added and the process continues
Usually several thousand mCi's are produced
Question - If 15mCi of 18F is calibrated for 10am, how many mCi are there if the dose was extracted from the cyclotron at 4am?