# An Active Irradiation System with Automatic Beam Positioning and Focusing for a Medical Cyclotron
## 4 Conclusions  
In the framework of the research program on radioisotopes for theranostics ongoing at the Bern medical cyclotron laboratory, a novel compact automatic focusing system (AFS) was conceived, realized and tested. It aims at enhancing the production performance using solid target stations. This apparatus is capable of focusing the beam on small targets down to 5 mm diameter or less and to keep it in position, thanks to a feedback algorithm that, based on the measurements of beam profiles, acts on a combined compact focusing and steering magnet, named Mini-PET Beamline (MBL). Beam tests were successfully carried out by installing the AFS at the end of the 6 m long beam transfer line (BTL). We demonstrated that the system is able to react to perturbations induced by changing the beam characteristics at the input of the MBL by acting on the focusing and steering elements of the BTL, assuring the convergence of the MBL coil currents towards an optimal radioisotope production. This optimization procedure minimizes the activation of the materials outside the target, thus optimizing radiation protection issues, transport procedure and use of the accelerator. For the same amount of extracted current, a gain factor of about 20 was found by comparing the worse case of a flat beam with an automatically optimized focused beam.  
On the basis of these promising results, the installation of the AFS in the bunker of the Bern cyclotron is planned, where the solid target station (STS) is in operation. Being about 1 m long, the AFS can be easily adapted to any existing medical cyclotron facility in view of investigations and applications of new radioisotopes for theranostics in nuclear medicine.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Produced Specific Activity** & **Produced Specific Activity** & **Total Charge on Target** \\  & \({}^{66}\)**Ga** \(\left[\frac{MBq}{g}\right]\) & \({}^{67}\)**Ga** \(\left[\frac{MBq}{g}\right]\) & **[nC]** \\ \hline Flat beam & \(53\pm 7\) & \((\,1.9\pm 0.3\,)\times 10^{-3}\) & 106.0 \(\pm\) 0.4 \\ \hline Focused beam & \(1180\pm 140\) & \((\,3.9\pm 0.6\,)\times 10^{-2}\) & 2074 \(\pm\) 8 \\ \hline
**Gain factor** & \(\mathbf{22\pm 4}\) & \(\mathbf{21\pm 4}\) & \(\mathbf{19.6\pm 0.1}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of gallium production using natural zinc targets with a flat and an optimized beam.  
**Author Contributions:** [PERSON] conceived the system; [PERSON] and [PERSON] contributed to its design and construction together with the LHEP mechanical workshop; [PERSON], [PERSON] and [PERSON] contributed to the installation of the system in the BTL; [PERSON] developed and implemented the automatic focusing feedback algorithm; [PERSON], [PERSON], [PERSON] and [PERSON] performed the beam tests; [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] contributed to the data analysis; [PERSON], [PERSON], [PERSON] and [PERSON] wrote the paper; [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] revised the paper; [PERSON] coordinated the project. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was partially funded by the Swiss National Science Foundation (SNSF). Grants: 200021_175749 and CRSII5_180352.  
**Acknowledgments:** We acknowledge contributions from the LHEP engineering and technical staff who helped us with the mechanical and electronics challenges during the prototype development and installation. We thank the SWAN Isotopen AG maintenance team for the collaboration.  
**Conflicts of Interest:** The authors declare no conflict of interest.