Image Artifacts From High-Z Materials in Proton Radiography Using High Energy 250 MeV Therapeutic Proton Beam
I Ali1*, S Ahmad1, N Alsbou2, (1) University of Oklahoma Health Sciences, Oklahoma City, OK, (2) Department of Engineering and Physics, University of Central Oklahoma, Edmond, OK
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PO-GePV-M-62 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: To investigate image artifacts induced by high-z materials in proton radiographs obtained by high energy beams from a proton therapy machine.
Methods: A high energy 250-MeV beam from the MEVION proton therapy system was used to irradiate a phantom that included different materials with low, intermediate and high z-composition and different shapes. The image quality of the proton radiographs was evaluated with the LEEDS phantom that is used usually for diagnostic kV-photon radiographs. The MEVION proton therapy machine provided open field beams of 25 mm diameter and depth ranges 5-32 cm. The proton images of different phantoms were captured with high spatial resolution and sensitivity phosphorus plates that are usually used in computed radiography. The proton radiographic images were captured at different depths of solid water 1-34 cm and separation between the phantom and CR plates downstream the proton beam.
Results: The intensities in the proton radiographs showed strong interference patterns around high-z materials. The interference patters depended on the composition of the density, position, shape and depth of the high-z objects in phantom. The image intensity varied significantly between the instructive and destructive interference patterns up to nearly 10% which resulted from the interference of the primary and scattered protons in the beam. The interference patterns varied with depth in phantom and positon of the high-z materials in the beam path. These scatter patterns occur upstream with the energetic protons and in the Bragg peak dose deposition region. These interference patterns affected the imaged quality where they degraded the spatial and contrast resolutions of the proton radiographs.
Conclusion: High-z materials induced strong image artifacts in proton radiographs acquired from high energy therapeutic proton beams. The intensity patterns resulting the interference of energetic primary and scatted protons affects the image quality of proton radiographs particularly spatial and contrast resolution.
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