Author: Salahuddin Ahmad, Imad M. Ali, Zaid Alkalani, Nesreen Alsbou 👨🔬
Affiliation: University of Oklahoma, University of Central Oklahoma, University of Oklahoma Health Sciences Center 🌍
Purpose: To design and evaluate a 3D-detector for proton CT-imaging and radiography, utilizing volumetric plastic scintillator detector exposed to high-energy therapeutic beams from proton therapy systems.
Methods: A novel 3D-detector was constructed to acquire proton radiographs using 227 MeV spot-scanning proton beams from the MEVION-S250i system. The detector consisted of layered plastic scintillator blocks with dimensions of 5x30x30 cm3 and a total thickness of 20 cm. The scintillation light produced by the proton beam fields of 20x20cm2 was captured by an array of cameras installed around the scintillators in a light-tight dark chamber. Testing included a range of phantoms such as head, thorax, and pelvis models.
Results: The captured projections from multiple camera views enabled successful reconstruction of proton radiographs. The proton beam ranges in the scintillators were employed to determine the water-equivalent thickness that represented the proton radiographic image contrast. This detector provided a water-equivalent, large-volume 3D solution with effective dimensions of approximately 30x30x20cm³, expandable through additional scintillator layers. Although the detector achieved high spatial and contrast resolutions across its continuous medium, the quality of proton radiographs was influenced by camera resolution (0.2mm) and sensitivity to the scintillation light. Limitations included reduced light transmission through scintillator slabs, camera sensitivity to emitted blue light, and a frame collection speed of 30 frames per second, which constrained beam tracking efficiency.
Conclusion: This plastic scintillator-based 3D-detector demonstrates a promising, tissue-equivalent solution for proton radiography with a large detection volume and high spatial resolution. Furthermore, this 3D-detector has potential to perform proton CT-imaging where the proton projections are acquired from different views to reconstruct proton CT-images. Its potential to address technical challenges in proton radiography makes it viable candidate for clinical applications, particularly as an alternative image-guidance method integrated into proton therapy systems that directly utilize therapeutic proton beams.