Deriving the mean excitation energy map from dual-energy and proton computed tomography.

The mean excitation energy, , is an essential quantity for proton treatment planning. This work investigated the feasibility of extracting the spatial distribution of by combining two computed tomography (CT) modalities, dual-energy CT and proton CT, which provided the spatial distribution of the relative electron density and the stopping power relative to water, respectively. We provided the analytical derivation of as well as its uncertainty. Results were validated on simulated X-ray and proton CT images of a digital anthropomorphic phantom. Accuracy was below 15% with a large uncertainty, which demonstrated the potential and limits of the technique.