Proton scatter radiography with integration-mode detectors by exploiting the West-Sherwood effect
Résumé
We present a model to analytically predict the transmitted protons fluence field on a rear integration-mode
detector. Multiple Coulomb scattering (MCS) is taken into account in the fluence signal and the West-
Sherwood effect due to transverse heterogeneities is highlighted. We then develop a gradient-based optimization method to retrieve the spatial variance of the Gaussian distribution in each pixel of the detector from the measured fluence. The initial estimation is obtained by correlating the measured attenuation to the variance when assuming a homogeneous water phantom. The proposed method was assessed on Monte Carlo simulation of a homogeneous water phantom containing or not a bone insert. The estimation results show that the algorithm can, under realistic experimental scenarios, retrieve the MCS spatial dispersion with reasonable accuracy for both phantoms. Furthermore, the West-Sherwood effect observed on fluence map is advantageously exploited to improve the quality estimation on tissue boundaries. These preliminary results indicate potential improvement of the spatial resolution of proton imaging using integration-mode detectors.