Using the Monte Carlo simulation tool GEANT4 we simulated the hadron-therapy beam line of the CATANA center. CATANA is the unique italian hadron-therapy facility in which 62 AMeV proton beams are used for the radiotherapeutic treatment of choroidal and iris melanomas. All the elements, such as diffusers, range shifters, collimators and detectors, typical of a proton-therapy line were modelled. The CATANA beam line provides an ideal environment for the experimental testing and validation of the software developed. The software architecture was developed, and now the validation of the software is in its final stage. Simulated ranges, energy distribution, depth and lateral dose distributions for full energy proton beams will be compared to the experimental results obtained at LNS with different detectors.