Development of a Quality Assurance Phantom for Proton Radiography Using High Energy Therapeutic Beams From Proton Radiotherapy Machines
C Pelas1*, N Alsbou2, S Ahmad1, I Ali1, (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-88 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To develop a quality assurance phantom for proton radiography with different materials to evaluate the image quality of proton radiographs obtained from energetic spot beam using a MEVION proton therapy machine.
Methods: The image quality of proton radiographs were evaluated quantitatively using different phantoms with materials (LEEDS and CIRS) to test parameters such as linearity, uniformity, contrast and spatial resolutions. Different tissue equivalent materials were used that included muscle, breast, adipose, liver, lung low, lung medium, bone. A high energy 230MeV-proton beam with a range of 32cm, spot size of 3.5mm and 2.5mm spacing from a MEVION proton therapy system was used to obtain the proton radiographs. One layer of energy modulation and the largest open proton field of 20x20cm2 was used. The proton radiographs were acquired on plastic (LYNX) and phosphorous scintillation plates (CR-plates).
Results: Similar to photon radiographs soft tissue materials with densities from air to bone were used to test the linearity of proton radiographs. Solid water phantom slab with uniform thickness worked well to test the image uniformity of the proton radiographs. The contrast resolution was tested with varying circular plugs that are made from muscle equivalent tissue impeded in solid-water phantoms. However, the spatial resolution of the proton radiographs was tested with Teflon line pairs instead of lead line pairs in the LEEDS-phantom used in photon radiographs. Large image artifacts were produced from proton beam scattering on high-Z materials. The CIRS-phantom has different materials that can be used to test reproducibility of the intensity values in the proton radiographs.
Conclusion: High-Z materials used to test image quality in kV-photon radiography were not appropriate for proton radiography. Quality assurance phantoms is an important tool to evaluate and control the image quality of proton radiographs and future applications in on-board image guidance systems for proton therapy.
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