Application of the HICAM camera for imaging of prompt gamma rays in measurements of proton beam range

The HICAM gamma camera is an imaging device recently developed in the framework of a European project, based on Silicon Drift Detectors (SDDs) as photodetectors. Although originally designed for low-energy gamma-ray imaging in nuclear medicine (140 keV of ^99mTc), in this work we attempt to use the camera, suitably modified, to image high energy prompt gamma rays (2 to 7 MeV) emitted by a target irradiated by protons. The final objective of our experiment is to assess the feasibility of proton beam range measurements by prompt gamma imaging with a slit camera, and the HICAM camera was chosen for a first prototype. Although a SDD-based camera would not be fast enough for real treatment conditions, the prototype here employed benefited from the camera modularity, compactness, high resolution and low noise. The camera here employed is composed of 25 SDDs of 1 cm² active area each, arranged in a 5×5 format, already used in clinical and research environments with a high intrinsic spatial resolution (~1 mm). The SDD matrix has been coupled to a LYSO crystal (1cm thickness), to improve efficiency with high-energy gammas, and has been characterized preliminarily with a ⁶⁰Co source. Good imaging performances have been obtained in this test. Moreover, results of a first test of the camera to detect prompt gammas emitted with a proton beam impinging on a plastic target are presented in this work.