Quantitative proton imaging from multiple physics processes: a proof of concept

Abstract

Proton imaging is developed in order to improve the accuracy of charged particle therapy treatment planning. It makes it possible to directly map the relative stopping powers of the materials using the information on the energy loss of the protons. In order to reach a satisfactory spatial resolution in the reconstructed images, the position and direction of each particle is recorded upstream and downstream from the patient. As a consequence of individual proton detection, information on the transmission rate and scattering of the protons is available. Image reconstruction processes are proposed to make use of this information. A proton tomographic acquisition of an anthropomorphic head phantom was simulated. The transmission rate of the particles was used to reconstruct a map of the macroscopic cross section for nuclear interactions of the materials. A two-step iterative reconstruction process was implemented to reconstruct a map of the inverse scattering length of the materials using the scattering of the protons. Results indicate that, while the reconstruction processes should be optimized, it is possible to extract quantitative information from the transmission rate and scattering of the protons. This suggests that proton imaging could provide additional knowledge on the materials that may be of use to further improve treatment planning.

Scattering proton CT

“…One way to correct for the under estimation in dense material would be to exploit its similarity to beam hardening and adapt strategies typically used in x-ray CT. Another option is to rely on iterative reconstruction and explicitly model the energy-dependence of MCS based on some a priori knowledge, as proposed by Bopp et al (2015). However, the MLP would need to be incorporated into the forward projection matrix to achieve best possible spatial resolution, which is probably more complicated in scattering proton CT than in energy-loss proton CT because the angular variance needs to be estimated from several trajectories at some point during the reconstruction.…”

“…The latter estimates the angular dispersion of protons due to MCS in the object and reconstructs a parameter describing MCS, e.g. radiation length (Bopp et al, 2013;Bopp et al, 2015;Taylor et al, 2016). An appealing practical aspect of scattering proton CT is that the imaging system is simpler than in energy-loss proton CT: it only requires tracking devices (to measure a proton's direction upstream and downstream of the object), but no detector to measure a proton's residual energy.…”

An experimental demonstration of a new type of proton computed tomography using a novel silicon tracking detector

“…22 Tomographic reconstructions of inverse scattering length (closely related to absolute scattering-power) have been demonstrated in simulation. 23,24 Further, we note that nuclear scattering tomography (NST) with protons has long been established, but this relies on very different principles (wide-angle single scattering). 25 In addition to demonstrating the first experimental CT images using multiple scattering, there are two noteworthy additional features of this work.…”

A pencil beam approach to proton computed tomography

“…The reconstruction procedure could be expressed as an iterative two-step process: the first allows estimation of the stopping power whereas the second uses the reconstructed RSP values to estimate the radiation length (and then the scattering power). 9 The updated scattering power can be used in the successive iteration for estimation of the stopping power and so on.…”

“…2 In addition, the information on the scattering and transmission rate of particles could bring complementary knowledge about the tissues. [7][8][9] In the pCT systems developed nowadays, protons are tracked before and after the passage through the patient with a dedicated system, providing information about the position and the direction of each proton. 10 A calorimeter (or range detector) is used to measure the residual energy of each proton downstream from the patient.…”