`Accurate Proton Range Shift Verification by Using a Two-Layer Dense-Pixel LYSO Compton Camera Prototype

Objective Compton camera (CC)-based prompt gamma imaging (PGI) is promising to realize real-time in-vivo range verification during proton therapy. Lutetium–yttrium orthosilicate (LYSO)-based CC has advantages in high detection efficiency and position resolution. However, few LYSO CC-based PGI experimental evaluations have been investigated. Approach We built a 46×46 two-layer dense-pixel LYSO CC prototype for PGI. We attempt the first-ever effort to conduct the proton range shift verification experiments with the LYSO CC prototype. A 13 MeV proton beam with a cross-section of 1 mm2 produced by the Compact Pulsed Hadron Source (CPHS) and a lead collimator irradiates a block of graphite, a block of polymethacrylates (PMMA) 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 peak current intensity was about 640 nA. The pulse width and frequency were 100 μs and 1 Hz, respectively. The rate of incident protons in each measurement is about 3.6×108 /s, and the corresponding delivered dose is about 5.8 Gy. Main results The built LYSO CC prototype can distinguish the displacement of the Bragg peak in 2 mm (reaching 1 mm) at a distance of about 13 cm, and can accurately reconstruct the positions of the Bragg peak with a mean deviation of 0.2 mm in the eighteen groups of experiments. Signification The experiments demonstrate the feasibility of the developed two-layer dense-pixel LYSO 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).