Automating Quality Assurance of a Medical Particle Accelerator Safety System Using a Formal Language Driven Test Stand

At the Centre for Proton Therapy at the Paul Scherrer Institute, cancer patients are treated with a fixed beamline and in two gantries for ocular and nonocular malignancies, respectively. For the installation of a third gantry, a new patient safety system (PaSS) was developed and is subsequently being rolled out to update the existing areas. The aim of the PaSS is to interrupt the treatment whenever any subsystem detects a hazardous condition. To ensure correct treatment delivery, this system needs to be thoroughly tested as part of the regular quality assurance (QA) protocols as well as after any upgrade. In the legacy safety systems, unit testing required extensive use of resources: 2 weeks of work per area in the laboratory in addition to QA beam time. In order to significantly reduce the time, an automated PaSS test stand for unit testing was developed based on a PCI eXtensions for Instrumentation chassis with virtually unlimited I/Os that are synchronously stimulated or sampled at 1 MHz. It can emulate the rest of the facility using adapters to connect each type of interface. With it, the PaSS can be tested under arbitrary conditions. A VHSIC (very high speed integrated circuit) hardware description language-based formal language was developed to describe stimuli, expected behavior, and specific measurements, interpreted by a LabView runtime environment. This paper describes the tools and methodology being applied for unit testing and QA release tests for the new PaSS. It shows how automation and formalization made possible to increase the test coverage while significantly reducing the laboratory testing time and facility's beam usage.