Presenter of 1 Presentation
BEAM MONITORING, CONTROL, AND TIME STRUCTURE VALIDATION USING A BEAM CURRENT MONITOR FOR A FLASH-ENABLED CLINICAL LINAC IN SUPPORT OF A CLINICAL TRIAL
Abstract
Background and Aims
There is a need for beam monitoring and feedback control systems for FLASH that are dose-rate independent and capable of controlling the beam at the level of individual pulses. We aim to use a beam current monitor (BCT) to measure dose in real-time, validate time structure of the beam, and build a feedback control loop.
Methods
We modified a 3D printed collimator for pre-clinical anatomy-specific irradiation of mice to accommodate a 55 mm diameter BCT positioned surrounding the beam path. The signal from the BCT was digitized on a fast oscilloscope. We determined the effect of the modified collimator with BCT on the entrance beam profile. The linearity of the BCT was established by varying dose per pulse in the range 0.2 to 2.3 Gy/pulse. The pulse width on the clinical linac was varied, and this change was measured using the BCT. Finally, the ability of the BCT to measure the variability of dose per pulse and pulse width due to a mistuned automatic frequency control (AFC) system was demonstrated.
Results
The BCT had minimal effect on the entrance profile and exhibited excellent linearity with dose per pulse up to 2.5 Gy/Pulse (R2 =0.99). The peak beam current for the 17 MeV FLASH beam was measured to be ~10 mA for a 2Gy/pulse output. Manual tuning of AFC showed the presence of a ramp-up in dose per pulse and pulse width. During the ramp-up period, the pulse width was observed to be as small as 0.5 us and the pulse output was 1/4th of the stable output.
Conclusions
We demonstrated real-time per pulse readout of electron beam charge, correlated with entrance dose. Going forward, we will perform a failure modes and safety analysis of the control system and assess long-term stability with the goal of supporting a human clinical trial.