Background: In medical cyclotron facilities, 11C is produced according to the 14N(p,α)11C
reaction and widely employed in studies of prostate and brain cancers by Positron Emission Tomography.
It is known from literature that the 11C-target assembly shows a reduction in efficiency during time,
meaning a decrease of activity produced at the end of bombardment. This effect might depend on aspects
which are still not completely known.
Objective: Possible causes of the loss of performance of the 11C-target assembly were addressed by
Monte Carlo simulations.
Methods: Geant4 was used to model the 11C-target assembly of a GE PETtrace cyclotron. The physical
and transport parameters to be used in the energy range of medical applications were extracted from
literature data and 11C routine productions. The Monte Carlo assessment of 11C saturation yield was
performed varying several parameters such as the proton energy and the angle of the target assembly
with respect to the proton beam.
Results: The estimated 11C saturation yield is in agreement with IAEA data at the energy of interest,
while it is about 35% greater than the experimental value. A more comprehensive modeling of the target
system, including thermodynamic effect, is required. The energy absorbed in the inner layer of the target
chamber was up to 46.5 J/mm2 under typical irradiation conditions.
Conclusion: This study shows that Geant4 is potentially a useful tool to design and optimize targetry
for PET radionuclide productions. Tests to choose the Geant4 physics libraries should be performed
before using this tool with different energies and materials.