Synchronized high‐speed scintillation imaging of proton beams, generated by a gantry‐mounted synchrocyclotron, on a pulse‐by‐pulse basis

Abstract

Background: With the emergence of more complex and novel proton delivery techniques, there is a need for quality assurance tools with high spatiotemporal resolution to conveniently measure the spatial and temporal properties of the beam. In this context, scintillation-based dosimeters, if synchronized with the radiation beam and corrected for ionization quenching, are appealing. Purpose: To develop a synchronized high-speed scintillation imaging system for characterization and verification of the proton therapy beams on a pulse-bypulse basis. Materials and methods: A 30 cm × 30 cm × 5 cm block of BC-408 plastic scintillator placed in a light-tight housing was irradiated by proton beams generated by a Mevion S250 proton therapy synchrocyclotron. A high-speed camera system, placed perpendicular to the beam direction and facing the scintillator, was synchronized to the accelerator's pulses to capture images. Opening and closing of the camera's shutter was controlled by setting a proper time delay and exposure time, respectively. The scintillation signal was recorded as a set of two-dimensional (2D) images.Empirical correction factors were applied to the images to correct for the nonuniformity of the pixel sensitivity and quenching of the scintillator. Proton range and modulation were obtained from the corrected images. Results: The camera system was able to capture all data on a pulse-by-pulse basis at a rate of ∼504 frames per second. The applied empirical correction method for ionization quenching was effective and the corrected composite image provided a 2D map of dose distribution. The measured range (depth of distal 90%) through scintillation imaging agreed within 1.2 mm with that obtained from ionization chamber measurement. Conclusion: A high-speed camera system capable of capturing scintillation signals from individual proton pulses was developed. The scintillation imaging system is promising for rapid proton beam characterization and verification.

A prototype scintillator real‐time beam monitor for ultra‐high dose rate radiotherapy

“…Several research programs are exploring FLASH-compatible beam monitors. 15,[17][18][19][20][21][22][23][24][25] Beam current transformer monitors 14,17,[19][20][21] gauge the beam intensity without introduction of a mass layer. They have been tested in a pulsed electron beam where the pulse rate is generally 100 Hz or less.…”

“…Such detectors, when placed in a proton beam, produce a scintillation light on a pulseby-pulse basis. 22 Another imaging system uses a CMOS camera to view a scintillator, but at a large distance, and was tested in a scanning pencil proton beam. 24,27 This is discussed later.…”

“…The promise of the emergence of the FLASH modality has prompted development of several beam monitoring technologies that might be deployed in experimental work and eventually in clinical trials and conventional therapeutic usage. Several research programs are exploring FLASH‐compatible beam monitors 15,17–25 …”

Ultra-fast, high spatial resolution single-pulse scintillation imaging of synchrocyclotron pencil beam scanning proton delivery

“…In contrast, Kanouta et al report a scintillation-based detector with sub-millisecond temporal resolution, but no ability to get 2D dose distributions (Kanouta et al 2022). Most recently, Goddu et al published on a scintillation imaging system of a passive scattering proton beam, where the system presented required light tight housing to image and imaged at 264 frames per second (Goddu et al 2022). Apart from this research, there have been limited advances in novel FLASH dosimetry methods.…”

Enhanced Cherenkov imaging for real‐time beam visualization by applying a novel carbon quantum dot sheeting in radiotherapy

“…This greatly increases the cost of the method. Meanwhile, although the time structure can be utilized for background subtraction, 19 however, this may not be possible with continuous irradiation sources such as those in Co‐60 Gamma Knife or proton systems based on isochronous cyclotron.…”