Optimization and verification of image reconstruction for a Compton camera towards application as an on-line monitor for particle therapy

Abstract

A: Particle therapy is an advanced cancer therapy that uses a feature known as the Bragg peak, in which particle beams suddenly lose their energy near the end of their range. The Bragg peak enables particle beams to damage tumors effectively. To achieve precise therapy, the demand for accurate and quantitative imaging of the beam irradiation region or dosage during therapy has increased. The most common method of particle range verification is imaging of annihilation gamma rays by positron emission tomography. Not only 511-keV gamma rays but also prompt gamma rays are generated during therapy; therefore, the Compton camera is expected to be used as an on-line monitor for particle therapy, as it can image these gamma rays in real time. Proton therapy, one of the most common particle therapies, uses a proton beam of approximately 200 MeV, which has a range of ∼ 25 cm in water. As gamma rays are emitted along the path of the proton beam, quantitative evaluation of the reconstructed images of diffuse sources becomes crucial, but it is far from being fully developed for Compton camera imaging at present. In this study, we first quantitatively evaluated reconstructed Compton camera images of uniformly distributed diffuse sources, and then confirmed that our Compton camera obtained 3 %(1σ) and 5 %(1σ) uniformity for line and plane sources, respectively. Based on this quantitative study, we demonstrated on-line gamma imaging during proton irradiation. Through these studies, we show that the Compton camera is suitable for future use as an on-line monitor for particle therapy.

Features of Particle and Heavy Ion Transport code System (PHITS) version 3.02

“…In addition, the competition between neutrons and γ -ray emissions can be considered in the improved GEM, whereas in the former version, it was presumed that an excited nucleus can emit γ -rays only when neutron emission is prohibited. These improvements allow PHITS to be used for prompt γ -ray analyses, which is useful for various purposes such as design of online trajectory imaging for charged-particle therapy based on gamma cameras [22].…”

Use of a Si/CdTe Compton Camera for In vivo Real-Time Monitoring of Annihilation Gamma Rays Generated by Carbon Ion Beam Irradiation

“…In this study, the peak intensities were not evaluated in a quantitative way. A quantitative analysis of Compton images is still at an early stage of development (49)(50)(51). Additionally, differentiating transported activated elements with annihilation gamma-rays from those generated at the irradiated site is not possible.…”

Multi-modal 3D imaging of radionuclides using multiple hybrid Compton cameras

“…The specific values applied to energy cut during each reconstruction are summarized in Table 4 . The number of iterations for the Compton mode and pinhole mode is determined by checking the convergence of the images 48 . The iteration number was 20 for the tri-modal demonstration and 10 for both bottles of drugs and mouse imaging.…”