Purpose: To test different materials and develop a quality assurance phantom to evaluate quantitatively the image quality of proton radiographs obtained from high energy scanning beams using the MEVION proton therapy system.
Methods: Different materials and phantoms (LEEDS and CIRS) were used to quantify the different imaging quality parameters of proton radiographs that included muscle, breast, adipose, liver, lung low, lung medium, bone. The images quality parameters that were tested included linearity, uniformity contrast and spatial resolutions. The proton radiographs were obtained using a high energy proton beam of 230MeV from the MEVION pencil-beam scanning proton therapy system. Proton pencil beams of a diameter of 3.5mm in air with a spot spacing of 2.5mm were used to obtain the proton radiographs. Large open proton beams of 20x20cm2 and range of 32cm in water with one energy layer modulation were used. Phosphorous scintillation plates that are usually used photon computed radiography were used to acquire the proton radiographs.
Results: High-Z materials such as lead, copper and other metals in the LEEDs phantom used for photon radiography were not appropriate for testing the image quality of the proton radiographs. Particularly the spatial resolution objects used for photon imaging did not work with proton imaging because the proton beam scattered with large angle degrading image quality. The contrast resolution was tested variable density and size plugs similar to the LEEDS phantom. The linearity of the proton radiographs was tested with inserts that are made from different tissue-equivalent materials with densities ranging from air to bone. The uniformity of the proton radiographs was tested using a solid water block.
Conclusion: This quality assurance phantom provides a useful tool to test and quantify the image quality of proton radiographs that can be used for image guidance with on-board imaging systems integrated with proton therapy machines.
Not Applicable / None Entered.