Dual beam-current transformer design for monitoring and reporting of electron ultra-high dose rate (FLASH) beam parameters


To investigate the usefulness and effectiveness of a dual beamcurrent transformer (BCTs) design to monitor and record the beam dosimetry output and energy of pulsed electron FLASH (eFLASH) beams in real-time,and to inform on the usefulness of this design for future eFLASH beam control.


Two BCTs are integrated into the head of a FLASH Mobetron system, one located after the primary scattering foil and the other downstream of the secondary scattering foil. The response of the BCTs was evaluated individually to monitor beam output as a function of dose, scattering conditions, and ability to capture physical beam parameters such as pulse width (PW),pulse repetition frequency (PRF), and dose per pulse (DPP), and in combination to determine beam energy using the ratio of the lower-to-upper BCT signal.


A linear relationship was observed between the absorbed dose measured on Gafchromic film and the BCT signals for both the upper and lower BCT (R2 > 0.99).A linear relationship was also observed in the BCT signals as a function of the number of pulses delivered regardless of the PW,DPP, or PRF (R2 > 0.99). The lower-to-upper BCT ratio was found to correlate strongly with the energy of the eFLASH beam due to differential beam attenuation caused by the secondary scattering foil.The BCTs were also able to provide accurate information about the PW, PRF, energy, and DPP for each individual pulse delivered in real-time.

*Ultra-High Dose Rate (UHDR) functionality for FLASH Radiotherapy is for investigational use only and is not cleared for sale by the US FDA.