Background and Aims

The radiobiological study of the FLASH effect requires accurate and reliable dosimetry. As scintillators are promising candidates, this work presents a first characterization of their response at UHDR, suggesting solutions to account for possible saturating effects.

Methods

Five scintillating fibers, one clinical and two experimental Y₂O₃:Eu-based scintillators (DoseVue N.V., Belgium) and two experimental Al₂O₃:C-based scintillators (SCK CEN, Belgium), were irradiated using the ElectronFlash system (SIT, Italy). Linearity with dose was validated by varying the number of pulses for both experimental Y₂O₃:Eu-based scintillators. Dose per pulse (DPP) linearity was investigated in all scintillators by varying pulse duration and the distance from the linac exit window (SSD). Pulse scheme stability was investigated by changing of the pulse repetition frequency (PRF).

Results

Good linearity with dose (R²>0.99) was observed in both experimental Y₂O₃:Eu-based scintillators. Linearity with increasing pulse duration (R²>0.95) and an inverse squared relation between DPP and SSD (R²>0.95) were observed in 4 out of 5 scintillators. However, a concave curvature in response, suggesting saturation, was observed for all scintillators. This effect was more pronounced for the smaller applicator diameter. Our results showed reduced saturation effects when increasing integration time as well as when reducing signal intensity. All scintillators showed a decreasing response with increasing PRF.

Conclusions

The promising characteristics of scintillators as on-line dosimeters for UHDR were validated and possible solutions to reduce saturation effects have been evaluated. Further research on the response by varying PRF is needed.

This work is part of the 18HLT04 UHDpulse project which received funding from the EMPIR programme.

Background and Aims

Dosimetry for FLASH radiotherapy, VHEE radiotherapy as well as for laser-driven beams cause significant metrological challenges due to the ultra-high dose rates and pulsed structure of these beams, in particular for real time measurements with active dosimeters. It is not possible to simply apply existing Codes of Practice available for dosimetry in conventional external radiotherapy here. However, reliable standardized dosimetry is necessary for accurate comparisons in radiobiological experiments, to compare the efficacy of these new radiotherapy techniques and to enable safe clinical application. UHDpulse aims to develop the metrological tools needed for reliable real-time absorbed dose measurements of electron and proton beams with ultra-high dose rate, ultra-high dose per pulse or ultra-short pulse duration.

Methods

Within UHDpulse, primary and secondary absorbed dose standards and reference dosimetry methods are developed, the responses of available state-of-the-art detector systems are characterised, novel and custom-built active dosimetric systems and beam monitoring systems are designed, and methods for relative dosimetry and for the characterization of stray radiation are investigated.

Results

Prototypes of different active dosimetry systems show promising results for real-time dosimetry for particle beams with ultra-high pulse dose rates. The results of the UHDpulse project will be the input data for future Codes of Practice.

Conclusions

A brief overview of the progress in the UHDpulse project and the involved institutions will be given.

Acknowledgement: This project 18HLT04 UHDpulse has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.