new imaging mode based on X-ray CT as prior image and sparsely sampled projections for rapid clinical proton CT

Proton computed tomography (CT) has a distinct practical significance in clinical applications. It eliminates 3&ndash;5% errors caused by the transformation of Hounsfield unit (HU) to relative stopping power (RSP) values&nbsp;when using X-ray CT for positioning and&nbsp;treatment planning systems (TPSs). Following the development of FLASH proton therapy, there are increased requirements for accurate and rapid positioning in TPSs. Thus, a&nbsp;new&nbsp;rapid proton CT imaging mode is proposed based on sparsely sampled projections. The proton beam was&nbsp;boosted to 350 MeV by a compact proton linear accelerator (linac). In this study,&nbsp;the&nbsp;comparisons of the proton scattering with the energy&nbsp;of 350 MeV and 230 MeV are conducted based on GEANT4&nbsp;simulations.&nbsp;As&nbsp;the sparsely sampled&nbsp;information associated with beam acquisitions at 12&nbsp;angles is not enough for reconstruction, X-ray CT is used as a prior image. The RSP map generated by converting the X-ray CT was constructed based on&nbsp;Monte Carlo simulations. Considering&nbsp;the&nbsp;estimation&nbsp;of the most likely path (MLP), the prior image-constrained compressed sensing (PICCS) algorithm is&nbsp;used to reconstruct images from two&nbsp;different phantoms using sparse proton&nbsp;projections of 350 MeV parallel proton beam. The results show that it is feasible to realize the proton image reconstruction with the rapid proton&nbsp;CT imaging proposed in this paper. It can produce RSP maps with&nbsp;much&nbsp;higher accuracy for TPSs and fast positioning to achieve ultra-fast imaging for real-time image-guided radiotherapy&nbsp;(IGRT) in clinical proton therapy&nbsp;applications.<br />&nbsp;