The Paul Scherrer Institute (PSI) is a multi-disciplinary research centre, located in Villigen, Switzerland and counts currently 1'200 staff members. The PSI developed and runs a radiation therapy facility and has been treating deep lying cancer tumours and eye tumours with protons since more than a decade. Based on this experience and treatment successes, the project PROSCAN has been launched having as objective the construction and operation of a state-of-the-art cancer therapy centre. PROSCAN includes a new proton accelerator, a new eye treatment system and a novel gantry for the treatment of deep lying tumours and aims at the development of new methods for cancer treatments with proton beams. During two project theses and a diploma thesis a real-time simulator (PROSim) was developed which simulates the proton beam current according to the nominal values of the beam line actuators. PROSim performs simulation calculations at a rate of 1 MHz, can simulate a wide variety of failure scenarios, and is reconfigurable online while it is in use. The main focus of the diploma thesis lays on the correct parameterization and the description of the actuators and sensors simulated with PROSim. With beam current measurements at the proton beam line, the parameters for the actuator and sensor simulations have been derived. By configuring PROSim with these parameters, the capability to simulate the proton beam current in good agreement with the measurements has been demonstrated. To increase the usability an application programming interface, simplifying the interaction with the simulator, has been implemented in C++ running on VxWorks.