Purpose: Proton radiography is a promising approach to reduce the uncertainty of patient positioning in proton therapy. Pixel detectors from high-energy physics are optimally suited for radiography due to their small pixel sizes and their proven radiation hardness. This paper presents first studies using pixel sensors developed for the ATLAS experiment at CERN in proton imaging. In addition, we present simulation results for the extension to a novel setup consisting of two detector planes.
Methods: A proton radiography setup is simulated consisting of a silicon detector with a pixel size of 50x250 µm² and an edge phantom as object. The framework Allpix2 simulates the interaction processes of protons, including multiple Coulomb scattering in the phantom, as well as signal generation of the readout chip. The achievable spatial resolution, quantified in MTF10%, is determined from simulations using phantoms made of different material compositions. Using a custom-made edge phantom at clinically relevant proton energies (70-220)MeV at the achievable edge resolution is determined.In the simulations of the two detector plane system, the radiography images are weighted with the individual scattering angles, which simplifies the edge detection.
Results: In simulation, filter-based image reconstruction shows resolutions between 3.5 line pairs per millimeter and 6 line pairs per millimeter, depending on which materials abut. Finally, measurements confirm the simulation results and show an edge resolution in the sub-millimeter range. A Toy model of the two detector plane system shows a reduction of the uncertainty on the edge position by 50% and a significantly improved edge resolution especially for small proton numbers.
Conclusion: In this study we demonstrate the feasibility of using pixel detectors developed for high-energy physics experiments in proton radiography. For a first application, a radiography measurement series is planned for a preclinical small animal irradiation.
Funding Support, Disclosures, and Conflict of Interest: The presented study was supported by the MERCUR-Stiftung graduate school "Praezisionsprotonentherapie -Praxisbezogene Physik und Chemie an der Schnittstelle zur Medizin" (grant number St-2019-0007).
Patient Movement, Radiography, Semiconductor Detectors
IM- Particle (e.g., Proton) CT: Development (New technology and techniques)