We propose a new type of optimised and highly sensitive beta-imaging camera with active background rejection POSICS for radio-guided surgery (RGS) and potentially for many other applications.

The RGS technique is used to help surgeons to locate precisely tumours, and minimise the surgical invasiveness thus improving patient life quality after the intervention. Currently, the beta-emitting radiotracers are mostly used in conjunction with gamma probes or gamma cameras. However, the exploitation of direct detection of positrons is still in an early stage of development. The direct detection of positrons can significantly improve the Signal-to-Noise Ratio (SNR), and then the sensitivity.

The proposed beta-imagining camera departs from what already developed so far for the use a novel active gamma background rejection based on two active detection layers. Each layer will be composed by a novel position sensitive SiPM (PS-SiPM) coupled with two different scintillator types: organic on top layer detect positrons, inorganic one with collimator on bottom layer to detect background gammas coming from positron annihilation, natural background radioactivity, patient body natural radioactivity. Active gamma background rejection has many important benefits as the use of smaller amount of radio-pharmaceutical tracers (dose) to spot tumours, or conversely to spot tumours of smaller size with commonly used doses and allow to use of RGS also in the case where the gamma-ray background from healthy organs presently does not allow it.

Arrays of SiPM devices are commonly used in many applications but they require a huge number of readout channels (e.g. 2.5 cm² of active area, to reach <1 mm resolution, needs 64 channels).
POSICS instead relies on the usage of novel position sensitive PS-SiPM, based on ‘charge sharing’ approach, having only 4 readout channels. The charge produced at the outputs allow identifying the interaction position of the events. Such approach would allow to reach ~1 mm resolution on 2.5 cm² of active area with only 4 read-out channels, i.e 16 times less number of channels with respect to standard arrays of SiPM.

This significant reduction of readout channels is important not only for the final product cost but also for the lower power consumption, which a relevant aspect for detector performance and for its engineering.

We will also investigate the possible scalability of such device, i.e. increase the sensitive area without increasing the number of read out channels. The proposed approach should be considered a first step towards the development of a new “LEGO brick”-like assembly of a position sensitive detectors, with interfaced readout electronics as a ready-to-use device for various applications in science and medical diagnostics. Such “LEGO bricks” would be tiled together to instrument big surface and have also the capability group readout channels to achieve the best trade-off between the resolution required and number of channels.