Investigation of SiPM performance Stability for On-line PET Imaging with Scanning Proton Pencil Beams

The objective of this study was to evaluate the performance of Silicon Photomultiplier (SiPM) change by radiation of neutrons induced by pencil scanning proton beam radiotherapy. Both dark current and gain changes of SiPM arrays were measured as they are the primary SiPM performance parameters. The experiment setup included a scanning proton pencil beam irradiated a human head phantom with SiPM arrays being placed nearby. Multiple repeated radiations and dark current/gain measurements were conducted. The results have shown that the impact of neutron radiations was negligible to small, with SiPM array's both dark current and gain changes less than around 1% to 2%, well within the experiment uncertainty, accumulated proton beam dose up to 12 Gy. In conclusion, for the specific pencil scanning proton beam with this study, there is unlikely any impact of neutron radiations to SiPM's performance within one fraction of the proton therapy, that is an important question for on-line PET image-based proton beam range monitoring. This conclusion is likely to be true for other pencil scanning proton beam facilities as well. On the other hand, the long term accumulated impact of neutron radiation to SPM's performance over multiple fractions of proton therapy is still an issue and should be addressed appropriately.