Search

At the Centre for Proton Therapy at the Paul Scherrer Institut we treat cancer patients using a fixed beam line and two gantries. The latter use a step-and-shoot technique to deliver dose covering the treatment volume with a grid of weighted proton bunches. Dose delivery for tumours moving under respiration (e.g. lung) is however challenging and not routinely performed because of the interplay between target and beam motions. At the Gantry 2 unit, we are implementing a novel continuous beam modulation concept called line scanning, aiming at realizing a faster dose delivery to allow for effective organ motion mitigation techniques such as rescanning and gating. The current should stabilise within 100 us, which is tough due to the non-linearity of the system and latency of the monitors. In this work we implemented a gain scheduled controller and a predictor by modelling the accelerator in Simulink and developing a controller using the frequency domain robust method. We used Mathwork’s HDL Coder functionality to generate VHDL code that was implemented in an FPGA in the gantry control system. Latency, overshoot and dosimetric performance improved considerably compared to a classic PID., Proceedings of the 12th Int. Workshop on Emerging Technologies and Scientific Facilities Controls, PCaPAC2018, Hsinchu, Taiwan

At the Centre for Proton Therapy at the Paul Scherrer Institute a cyclotron, two gantries and a fixed beamline are being used to treat tumours. In order to prevent non-optimal beam delivery, an interlock patient safety system (PaSS) was implemented that interrupts the treatment if any sub-system reports an error. To ensure correct treatment, the PaSS needs to be thoroughly tested as part of the regular quality assurance as well as after each change. This typically required weeks of work, extensive beam-time and may not comprehensively detect all possible failure modes. With the opportunity of the installation of a new gantry, an automated PaSS test stand was developed that can emulate the rest of the facility. It consists of a NI PXI chassis with virtually unlimited IOs synchronously stimulated or sampled at 1MHz, a set of adapters to connect each type of interfaced signal and a runtime environment. We have also developed a VHDL based formal language to describe stimuli, assertions and specific measurements. We present the use of our test stand in the verification and validation of the PaSS, showing how its full quality assurance, including report generation was reduced to minutes., Proceedings of the 16th Int. Conf. on Accelerator and Large Experimental Control Systems, ICALEPCS2017, Barcelona, Spain

Patient treatments in scanned proton therapy exhibit dead times, e.g. when adjusting beamline settings for a different energy or lateral position. On the one hand, such dead times prolong the overall treatment time, but on the other hand they grant possibilities to (retrospectively) validate that the correct amount of protons has been delivered to the correct position. Efforts in faster beam delivery aim to minimize such dead times, which calls for different means of monitoring irradiation parameters. To address this issue, we report on a real-time beam monitoring system that supervises the proton beam position and current during beam-on, hence while the patient is under irradiation. For this purpose, we sample 1-axis Hall probes placed in beam-scanning magnets and plane-parallel ionization chambers every 10 μs. FPGAs compare sampled signals against verification tables - time vs. position/current charts containing upper and lower tolerances for each signal - and issue interlocks whenever samples fall outside. Furthermore, we show that by implementing real-time beam monitoring in our facility, we are able to respect patient safety margins given by international norms and guidelines., Proceedings of the 16th Int. Conf. on Accelerator and Large Experimental Control Systems, ICALEPCS2017, Barcelona, Spain

Paul Scherrer Institute currently extends its PROSCAN facility with a third gantry treatment room - Gantry 3, which is realized in a research collaboration with Varian Medical Systems. The main research goals at the PROSCAN facility include further development of precise spot scanning and optimized beam delivery with low dead-time for treatment of moving targets. Consequently Gantry 3 is designed to feature advanced pencil beam scanning technology with a large scan field size of 30x40cm, integrated cone beam CT functionality and will in the future allow fast energy layer switching. The main challenge in realizing Gantry 3 is the integration of the Varian Gantry into the existing PROSCAN control system environment, allowing seamless beam operation. Installation of the additional treatment room has started in summer 2015 followed by the integration and technical commissioning phases of the Gantry in 2016, all during full operation of the existing treatment areas at our facility. We report about the special challenges and achieved performance results during commissioning of the Varian Gantry system in combination with the PSI PROSCAN facility., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

A new gantry for cancer treatment is being installed at the Proton Therapy Centre in the Paul Scherrer Institut (PSI), where already two gantries and a fixed line operate. A protection system is required to ensure the safety of patients, requiring stricter redundancy, verification and quality assurance (QA) measures than other accelerators. It supervises the Therapy System, sensors, monitors and operator interface and can actuate magnets and beam blockers. We built a reusable framework to increase the maintainability of the system using the commercial IFC1210 VME controller, developed for other PSI facilities. It features a FPGA implementing all the safety logic and two processors, one dedicated to debugging and the other to integrating in the facility's EPICS environment. The framework permitted us to reduce the design and test time by an estimated 40% thanks to a modular approach. It will also allow a future renovation of other areas with minimum effort. Additionally it provides built-in diagnostics such as time measurement statistics, interlock analysis and internal visibility. The automation of several tasks reduces the burden of QA in an environment with tight time constraints., Proceedings of the 15th Int. Conf. on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2015, Melbourne, Australia