A TOPAS model for lens-based proton radiography.

Area of Science:

• Medical Physics
• Radiological Imaging
• Particle Therapy

Background:

• Proton radiography offers potential for patient positioning, real-time stopping power estimation, and adaptive therapy.
• Monte Carlo simulations using TOPAS enable advanced modeling of proton and heavy ion treatments and imaging.

Purpose of the Study:

• To evaluate lens-based proton radiography as an instantaneous imaging technique.
• To model the magnetic lens system at LANSCE for proton radiography simulations.
• To assess image quality and contrast at various proton energies and collimation levels.

Main Methods:

• Modeled a four-quadrupole magnetic lens system in TOPAS for an 800-MeV proton beamline.
• Simulated imaging of various objects at energies from 230-930 MeV with different collimator settings.
• Scaled magnetic field strength with particle relativistic factor (βγ).

Main Results:

• High-Z materials (gold, gallium, bone) provided greater contrast than low-Z materials (water, lung).
• A 5-mrad collimator enhanced tissue-to-contrast agent contrast; a 10-mrad collimator improved differentiation of high-Z materials.
• Image quality improved with energy, achieving sub-mm resolution at 630 MeV, though water-equivalent path length required calibration.

Conclusions:

• Proton radiography is viable for shallow bone imaging at 330 MeV and deeper structures at 630 MeV.
• High-Z contrast agents enhance visibility, making the modality suitable for carbon therapy centers.
• The developed TOPAS model supports advanced simulations for proton therapy and particle imaging.