Room: AAPM ePoster Library
Purpose: Dark field proton radiography combines the principles of Schlieren optical imaging, or dark field X-radiography, with lens-based proton radiography. The aim is to provide an instantaneous measure of proton stopping power, with the highest amount of information per dose deposition possible.
Methods: A dark field condition was created by applying a pre- and post-collimation scheme to the high energy proton radiography facility at Los Alamos Neutron Science Center. With a cut angle that removes protons of less than 2 mrad of scatter upstream, and more than 2 mrad of scatter downstream, the default is to have zero transmission until an object is present. Proton radiographs are acquire with no object, thin gold phantoms, and 20-cm thick acrylic phantoms to compare between a conventional proton radiographic setup and the dark field proton radiographic setup.
Results: Dark field proton radiographs of a thin gold foil phantom demonstrate an SNR improvement of a factor of 2 over conventional proton radiography. Sensitivity to changes in water equivalent path length in 20-cm of acrylic was improved from 1% with standard proton radiography, to 0.25% with dark field proton radiography.
Conclusions: Initial results indicate that the system provides a sensitivity improvement to subtle areal density variations within thick objects. This is likely due to two effects: the removal of highly scattered protons before the object location, and the removal of unscattered protons after the object location. The protons remaining carry the highest amount of radiographic information and a lower amount of noise. This could have implications for beam's-eye-view image guidance for proton therapy, or for treatment planning, where increasingly accurate measures of water equivalent path length translate directly into increased estimates of dose deposition.