This project aims at verifying and comparing various Dual-energy CT (DECT) based analytical methods to predict tissue properties and relative stopping power (SPR) values for use in proton therapy.The relative (to water) proton stopping power has been experimentally verified using fresh tissue samples and dosimetric gel, showing a marked improvement of accuracy for DECT over single energy CT (SECT). The reliability of different Hounsfield-units (HU) to SPR conversion algorithms has also been thoroughly assessed for DECT data acquired using different CT scanners. An ongoing analysis of already acquired PET scans and planned prompt gamma measurements will enable verifying the ability of DECT in predicting tissue compositions.