Performances of the beam monitoring system and quality assurance equipment for the HIMM of carbon-ion therapy.

PURPOSE

The heavy-ion medical machine (HIMM), which is the first commercial medical accelerator designed and built independently by the institute of modern physics (IMP) in Wuwei, Gansu Province, China, had officially completed clinical trials at the time of this article's writing. Three types of detector systems were developed based on the ionization-chamber principle to monitor the beam parameters during treatment in real time, quickly verify the beam performance during a routine checkup, and ensure patient safety.

METHODS AND MATERIALS

The above-mentioned detector systems were used for beam monitoring and quality assurance in the treatment system. The beam-monitoring system is composed of three integral ionization chambers (ICs) and two multistrip ionization chambers (MSICs) as a redundant design. The irradiation dose, beam position, and homogeneity of a lateral profile are monitored online by the beam-monitoring system, and safety interlocks are established to keep the test results under the predefined tolerance limitation. The quality-assurance equipment was composed of one MSIC and one IC stack. The IC stack was used for energy verification.

RESULTS

The off-axis response of ICs is within a tolerance of 2%, and the dose interlock system (DIS) response time is less than 7 ms during the treatment process. The positioning resolution of MSICs reached 73 µm. The IC stack can verify the beam range within one spill and the measurement resolution is less than 0.2 mm.

CONCLUSIONS

The beam-monitoring system (BMS) and quality-assurance equipment (QAE) have been installed and run successfully within HIMM for two years and are associated with the HIMM treatment system to deliver the right dose to the correct position precisely. Furthermore, the daily QA task is simplified by it. Above all, the system has passed the performance test of the China Food and Drug Administration (CFDA).