Background and Aims

FLASH radiotherapy requires the development of new detectors to be able to cope with ultra-high-pulse-dose-rates (UHDpulse) beams. This work aims to test customized Timepix3 detectors to identify the most suitable sensor and settings to be used for the characterization of stray radiation produced in UHDpulse proton beams (PB).

Methods

Dose rates (DR) exceeding 160Gy/s were delivered by a pencil proton beam of 220MeV energy at the University Proton Therapy Dresden, Germany. For data collection two customized semiconductor pixel detectors, Timepix3 ASIC chip, with electronics placed on a flexible cable (50mm distance from the sensor, Fig. 1) were immersed, in turns, inside a water-phantom. The detectors were moved laterally at different depth during irradiation.

Figure 1. Experimental setup with Minipix-Timepix3-Flex detector placed in a waterproof cadge.

Results

The Minipix-Timepix3-Flex detector (Fig. 1) provides ns timing resolution at the pixel level together with quantum-imaging sensitivity with 100% detection efficiency for heavy-charged particles. The integrated per-pixel deposited energy, number of registered events, and DR were measured (Fig. 2).

Figure 2. The plots show the spatial distribution of integrated deposited energy at 50mm (left) and 100mm (right) behind Bragg Peak for a 2ms proton pulse measured with Minipix-Timepix3 with 100µm (top) and 650µm (bottom) thick silicon sensor.

Conclusions

A detector equipped with a thinner silicon sensor, 100µm, is more suitable for UHDpulse PB measurements due to the reduced amplitude of the signal and pixel size, allowing to register higher event rates.

Acknowledgements: This work was supported by the 18HLT04UHDpulse project founded by EMPIR-programme and EU INSPIRE (730983) project.