Proton computed tomography (pCT) is an imaging modality which provides several benefits including the accurate estimation of the relative stopping power (RSP) distribution for proton therapy treatment planning. Conventional proton CT scanners measure the energy loss of each proton individually, along with their positions and directions before and after the object, to estimate the integral of the RSP along each proton’s most likely path (MLP).
However, keeping reasonable acquisition times and moderate manufacturing costs with this design is challenging. As a potential solution, a novel design was recently proposed where the RSP distribution is inferred from the time-of-flight (TOF) of protons between two detectors sandwiching the object, without needing a residual energy tracker. However, a major difficulty stems from this new design: to each measured TOF corresponds infinitely many possible water-equivalent path lengths (i.e., RSP integrals) because the velocity of the proton depends on the order of the materials encountered along the MLP. Consequently, no reconstruction algorithm is currently available for this set-up.
In this talk, I will present two reconstruction procedures that are currently under investigation at the CREATIS laboratory (Lyon, France).