Measurement of activity produced by low energy proton beam in metals using off-line PET imaging

In this work, we investigate PET imaging with ⁶⁸Ga and ⁶⁶Ga after proton irradiation on a natural zinc foil. The nuclides ⁶⁸Ga and ⁶⁶Ga are ideally suited for off-line PET monitoring of proton radiotherapy due to their beta-decay half-lives of 67.71(9) minutes and 9.49(3) hours, respectively, and suitable β end-point energy. The purpose of this work is to explore the feasibility of PET monitoring in hadrontherapy treatments, and to study how the amount of activity and the positron range affect the PET image reconstruction. Profiting from the low energy reaction threshold for production via (p,n) reactions, both ⁶⁸Ga and ⁶⁶Ga gallium isotopes have been produced by activation on a natural zinc target by a proton pencil beam. In this way, it is possible to create detailed patterns, such as the Derenzo-inspired one employed here. The proton beam was produced by the 5 MV tandetron accelerator at CMAM in Madrid. The energy of this beam (up to 10 MeV) is similar to the residual energy of the protons used for therapy at the distal edge of their path. The activated target was imaged in an ARGUS small animal PET/CT scanner and reconstructed with a fully 3D iterative algorithm, with and without positron range corrections.