Epics-based Control System for a Radiation Therapy Machine

The clinical neutron therapy system (CNTS) at the University of Washington Medical Center (UWMC) has been treating patients since 1984. A new EPICS-based therapy control program replaces a locally-developed C program used since 1999. The new program retains the original safety philosophy and delegation of functions among nonprogrammable hardware, PLCs, microcomputers with programs in ROM, and general-purpose computers running high-level language programs. The latter are used only for data-intensive, prescription-specific functions. The therapy control portion uses a single soft IOC for control and a single EDM session for the operator’s console. Prescriptions are retrieved from a PostgreSQL database and loaded into the IOC by a custom client program. The system remains safe if the computers or their programs crash or stop producing results. Different programs at different stages of the computation check for invalid data and other faults. Development activities include formal specifications and automated testing which avoid, then check for, design and programming errors.