Optimized conversion from CT numbers to proton relative stopping power based on proton radiography and scatter corrected cone-beam CT images

International audienceWe propose a method to generate accurate proton relative stopping power (RSP) maps from patient cone-beam CT (CBCT) images. The scatter polluted low frequency component in the CBCT projections is replaced by an analytically calculated estimate of the scatter-free component. This is obtained by forward projecting the segmented CBCT image overridden with reference materials (air, soft tissue, bone). The projection model accounts for polychromaticity and uses an estimate of the combined source-detector spectral function. High and low frequency image components are automatically matched. The accurate conversion curve from CT numbers to RSP is obtained by comparison of a proton radiography and a proton digitally reconstructed radiography. CBCT images are acquired on a clinical scanner and proton images are simulated by Monte Carlo. Results show clearly reduced cupping effect and overall better RSP accuracy when CBCT images are scatter corrected