FLASH Radiotherapy (RT) is a potentially new cancer radiotherapy technique
where an entire therapeutic dose is delivered in about 0.1 s and at ~1000 times
higher dose rate than in conventional RT. For clinical trials to be conducted
safely, precise and fast beam monitoring that can generate an out-of-tolerance
beam interrupt is required. A FLASH Beam Scintillator Monitor (FBSM) is being
developed based in part on two novel proprietary scintillator materials: an
organic polymeric material (PM) and inorganic hybrid (HM). The FBSM provides
large area coverage, low mass profile, linear response over a broad dynamic
range, radiation tolerance, and real-time analysis IEC-compliant fast
beam-interrupt signal. This paper includes the design concept and test results
from prototype devices in radiation beams that include heavy ions, low energy
protons at nA currents, FLASH level dose per pulse electron beams, and in a
hospital radiotherapy clinic with electron beams. Results include image
quality, response linearity, radiation hardness, spatial resolution, and
real-time data processing. PM and HM scintillator exhibited no measurable drop
in signal after a cumulative dose of 9 kGy and 20 kGy respectively. HM showed a
small -0.02%/kGy signal decrease after a 212 kGy cumulative dose resulting from
continuous exposure for 15 minutes at a high FLASH dose rate of 234 Gy/s. These
tests established the linear response of the FBSM with respect to beam
currents, dose per pulse, and material thickness. Comparison with commercial
Gafchromic film indicates that the FBSM produces a high resolution 2D beam
image and can reproduce a nearly identical beam profile, including primary beam
tails. At 20 kfps or 50 microsec/frame, the real-time FPGA based computation
and analysis of beam position, beam shape, and beam dose takes < 1 microsec.Comment: 15 pages, 9 figure