Purpose: To provide and demonstrate a feasibility study on using proton induced acoustic signals as a means for proton radiography imaging. The advantages of conventional proton radiography are a more accurate estimation of stopping power ratios for improved treatment planning and verification, and the images are obtained from the beam’s-eye-view of the proton system. The disadvantages are large and expensive implementation of equipment, inferior image quality arising from the multiple scatter phenomena of protons, and dose deposition distal to the planned target volume. The goal is to find a solution that can maintain the advantages of conventional proton radiography, mitigate the disadvantages, while utilizing a method that provides promise for imaging.
Methods: Utilizing the K-wave toolbox in MATLAB, a two-dimensional 5.12-by-5.12cm, 0.1mm resolution simulation environment was created with a sound speed and density like that of water. Five 0.3-by-0.3mm markers with characteristics that mimic aluminum were inserted into the center of space, separated by 2mm. 512 single element sensors in a single-directional orientation were inserted on the edge of the entrance side. A 20MeV proton beam with a 0.1mm resolution was inserted just beyond the sensor elements for an initial pressure distribution. In each sensor element, the signal reflected off the markers was isolated from the signal generated from the initial pressure distribution and subsequently reconstructed.
Results: Images for a reconstruction and non-negative reconstruction were generated. In each image, the five markers can clearly be distinguished from the surrounding medium.
Conclusion: While this method is yet to be experimentally demonstrated, this proof-of-concept simulation indicates the potential for successful implementation in the clinic. This proposed technique can have a place in clinical workflow with applications in patient setup verification and motion management, while providing similar advantages as conventional proton radiography such as obtained stopping power information and a beam’s-eye-view geometrical orientation.