Self-sufficient safety facility ASE_1

In co-operation with the University Clinical Centre Benjamin Franklin, the Helmholtz-Zentrum Berlin developed Germany's first eye tumor therapy workstation. Since August 1998 patients with tumors on the retina have been treated  with a healing chance  above 90%. During the irradiation of eye tumors with protons high safety standards are in force. The individual dose rate calculated by the physician must be kept exactly. In particular, an increased dose rate and irradiation inhomogeneities must be avoided securely.

The self-sufficient safety facility ASE developed and built by the TOSS GmbH is an autonomous process checking and control unit. It is based on a redundant two-processor system. There are two processor types: the main processor HP and the redundancy test processor RTP. They monitor the process cycle independently after a given setting of parameters and inform themselves online about seen process conditions. The ASE represents an independent unit of the entire security concept spatially separated by the treatment workstation of the physician. Its function consists of the checking of measuring signals and status information to be won for the observance of limit values from the therapy facility and of the immediate interruption of the path of rays  in the case of exceeding limit values, not to endanger the health of patients and treating persons.

• Control unit as a redundant 4-processor system, processor base Infineon XMC 4500 ARM Cortex-M4 32 bit processor core
• control unit: colour LCD display with touch function
• Real-time clock for the time stamp
• Parallel coverage and evaluation of 32 analogous and 32 digital process signals
• Evaluation separated according to decision criteria capable for editing
• 2 independent self-preservation systems
• Valuation criteria for each channel separately definable
• Analogously: 0..5V high /low voltage level, resolution 0,01V
• Digitally: specified condition 0/1
• Offsetting of several input signals to symmetry pictures
• Fast 16 bit ADC 500 ns
• Frequency counting for the monitoring of a modulator wheel
• 6-channel event counting for the registration of the ionization chambers
• Cycle time max. 1 ms raster
• graduated disconnection of 4 shutters for interruption of the path of rays

In 1997 the TOSS company developed and produced the socalled self-sufficient safety facility (ASE) for the eye tumor therapy team (ATT) at the HMI.

Till now, the heavy ion accelerator for the irradiation therapy in humans has been exclusively used for the eye tumor therapy with highly energetic protons. In the medical irradiation therapy, there are strong safety standards defined within the norms for medical electron accelerators (DIN 6847). In the scope of the therapy project at the HMI, it was, therefore, necessary to guarantee the appropriate safety standards. With the ASE, an interlock system was developed to ensure the safety of the patients during the irradiations. The ASE monitors important parameters of the therapy via analogous and digital input channels, as well as input counters and carries out the turn off of the proton beam in the case of registered differences from given safety conditions. In addition, extensive internal function tests and protocol functions were realized. As a redundantly produced autonomous process monitoring and control unit, the ASE is the central security element of the therapy process.

The ASE and its documentation were part of an administrative expert examination for the permission of the therapy process, because an irradiation therapy with highly energetic protons was not yet existing in Germany. Both of it were accepted without objection. With that and the high quality of the work, the TOSS company considerably contributed to the successful start of the proton therapy in Germany.

Moreover, assessing the work, there are to pronounce the very good observance of dates and the permanent availability, which, in particular, were very important in preparing the expert examinations.

We, therefore, can recommend the TOSS company for the carrying out of jobs with highly safety-relevant standard in the way mentioned without reservation.

Original in German