Program Information
A New Technique for Increasing Spatial Resolution of Proton Radiography
A Hammi*, D Weber , A Lomax , Paul Scherrer Institut, Villigen-PSI, Switzerland
Presentations
SU-F-601-1 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: 601
Purpose: To improve the limited clinical usability of integrated pencil beam proton radiography (PR), we present a method that improves both spatial and density resolution of radiography systems conceptually designed for PBS techniques without event-tracking equipment.
Methods: Using Computed Tomography data (CT), a radiographic proton pencil beam (PB) was simulated using Monte Carlo with an in-air beam profile of 8 mm FWHM and on a two dimensional grid of 5 x 5 mm. The residual Bragg peaks (RBP), as would be measured in a range telescope behind the patient, were then analyzed. Due to patient heterogeneities and the finite width of the proton PB, this resultant RBP can be considered to be a superposition of a set of weighted and shifted pristine Bragg peaks (range dilution), which are related to the density heterogeneities through which the PB passed. This concept has been exploited here to increase the resolution of PR by applying an appropriate optimization to de-convolve the RBP into this set of individual pristine BP’s. Together with a-priori knowledge of the geometric information from the planning CT, these range spectra were then combined with water-equivalent-path-lengths obtained from the CT, such that only BP’s considered were those that had passed directly through the patient, thus reducing the contribution from scattered protons.
Results: The optimized PR demonstrates a minimum 4 times higher special resolution than the nominal resolution. Agreement between the optimized PR and the ground truth DRR were 95.3%, 91.22%, 84.82% for a distance-to-agreement and a relative WET deviation of 2 mm/2%, 1 mm/1%, 0.5 mm/0.5% respectively.
Conclusion: A technique to extract sub-pencil beam resolution density heterogeneities for range-probe-based proton radiography can substantially increase spatial resolution and reduce patient delivered dose by factor 4, without restricting image quality.
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