TH-CD-BRA-09: Quality Assurance of Scanned Proton Beams with a Volumetric Liquid Scintillator Detector

Abstract

Purpose: To develop a volumetric scintillation detector capable of quickly and accurately measuring the range, lateral profile, and lateral position of scanned proton beams. Methods: A volumetric scintillation detector was constructed, consisting of a tank of liquid scintillator imaged on two sides by CCD cameras. The cameras measured orthogonal projections of the emitted light in cine mode at frame rates of 1 frame/s or 37 frames/s, depending on the proton beam delivery rate. Proton beams with 60 energies ranging from 72.5 to 168.8 MeV were measured in a single delivery sequence, requiring less than 3 minutes of beam time to measure the range and lateral profile. The measured range and lateral profile width were compared with the nominal beam ranges and the lateral profiles measured with an ionization chamber. A 3×3 grid of proton beams with 5 cm spacing at 5 different energies was also measured, and the lateral position of each beam was compared with its nominal position. Results: The mean difference between the measured and nominal beam ranges was 0.1 mm (σ=0.1 mm), with a maximum difference of 0.3 mm. The differences between the measured and nominal lateral beam positions ranged from 0.22 mm to 2.64 mm, with the errors increasing with distance from the center of the detector. The lateral beam profile widths were systematically 1 mm narrower than reference measurements using an ionization chamber. Conclusion: The detector described in this study can provide fast, high-resolution measurements of the range, lateral profile, and lateral position for scanned proton beams. The ability of the detector to rapidly measure proton beam characteristics at multiple energies makes it particularly promising as a tool for scanned proton beam quality assurance.