Accurate Range Shift Verification by Using a Dual-View LYSO-LaBr3 Compton Camera Prototype during Proton Beam Irradiation

Compton-based prompt gamma imaging (PGI) is promising to realize a real-time range verification for in-vivo beams during proton therapy. However, the resolution of the real-world detectors and the detection efficiency under the clinical dose rate limit the actual application of the Compton camera (CC). Besides, the background noise caused by the secondary neutrons and protons further degrades the spatial resolution of the CC in the PGI. To meet the requirement of the high-resolution and low-background 3D PGI, we attempted the first-ever effort to develop a novel dual-view Compton camera prototype. The developed dual-view LYSO-LaBr
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CC utilized the projection data obtained by the different CC to extract feature information and eliminate the background noise. Meanwhile, the prototype overcomes the problem of distortion in the direction perpendicular to the detector plane during the 3D reconstruction of a single Compton camera. A 13 MeV proton beam with a cross-section of 1 mm
²
irradiates a block of graphite, a block of polymethacrylates, and a block of fresh pork, respectively. A range shift varied from 1 mm to 5 mm of the proton beam is used to evaluate the performance of the prototype in PGI. The current intensity was about 640 nA. The pulse width and frequency were 100 μs and 1 Hz, respectively. The number of incident protons in each measurement was about 3.6×10
⁸
. The developed CC prototype could distinguish the displacement of the Bragg peak in 2 mm (reaching 1 mm) at a distance of about 13 cm. The mean deviation of the reconstructed positions of the Bragg peak was 0.13 mm in the eighteen groups of experiments. The experiments demonstrate the feasibility of the developed dual-view LYSO-LaBr
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CC in realizing accurate range shift monitoring and show its potential in range verification during clinical proton therapy and high particle rate proton therapy (e.g. FLASH proton therapy).