Purpose: Dosimetry is one of the fundamental issues that presents challenges to clinical implementation of FLASH radiation therapy. The purpose of this study is to investigate the usefulness and effectiveness of toroids to monitor the output and the energy of pulsed electron FLASH beams in real-time.
Methods: The FLASH Mobetron (IntraOp, Sunnyvale, CA, USA) is a compact commercial linear accelerator that delivers pulsed electron beams at conventional (~10 Gy/min) and FLASH (>40 Gy/s) dose-rates for energies from 6 to 9 MeV. The Mobetron is equipped with two passive toroid detectors, one located after the primary scattering foil, and one located after the internal ion chamber and before the optics in the head.
Results: Our findings show a linear relationship between the absorbed dose and the toroid signal for both the upper and lower toroids. This leads to the observation that each toroid can be used independently to monitor the dose delivery of a FLASH electron beam, replacing the traditional MU1 and MU2 chambers. The ratio of the signals between the upper and lower toroid shows a linear correlation to the energy of the beam and to the treatment depth as well, as represented by the R50 and R80 of the beams investigated, respectively.
Conclusion: The dual toroid setup in the FLASH Mobetron machine has shown to be a reliable dose monitoring system for FLASH electron beams and the ratio between the two has a strong relationship with beam energy. Due to the fast signal readout and processing on the time scale of ≤ 1 ms, the toroids can be used to provide real-time dose and energy monitoring, thus proving to be a valid and adequate system for FLASH electron beam control, similar to the function of the dual transmission chamber system used in conventional clinical linear accelerators.
Dosimetry Protocols, Radiation Detectors, Radiation Dosimetry
TH- Radiation Dose Measurement Devices: Development (new technology and techniques)