Nonnegative Gaussian process tomography for generalized segmented planar detectors

Abstract

The concept of Gaussian process tomography along with nonnegative constraints is applied in the context of high-resolution image reconstruction using segmented planar detectors with few readout channels. Expanding on the concept of 2-D projections onto strip-like readout segmentations, 3-D projections as well as more generalized detector segmentation and readout channel mappings are explored. A focus is placed on reconstructing dose distributions in proton therapy pencil beam scanning, and a fast, approximate approach to applying nonnegative constraints is developed and motivated for use in proton therapy beam imaging.

A 2D strip ionization chamber array with high spatiotemporal resolution for proton pencil beam scanning FLASH radiotherapy

“…In general, the reconstruction of the full 2D distribution from two 1D projections is not possible. 38,39 However, the characteristics of modern proton PBS systems allow one to make reasonable assumptions (e.g., circular symmetry of the pencil beam spot profile) about the full 2D beam spot profile, thus making it possible to perform reconstructions of the 2D dose distribution. With the combination of the measured spot position, 1D profiles, intensity, and reasonable assumptions about the 2D spot profile, the reconstruction of the 2D dose distribution has been performed and good agreement with a discrepancy within 2% has been achieved with the Markus chamber and film dosimetry.…”

“…The measurements obtained from strip detectors are projections in nature of the 2D distributions. In general, the reconstruction of the full 2D distribution from two 1D projections is not possible 38,39 . However, the characteristics of modern proton PBS systems allow one to make reasonable assumptions (e.g., circular symmetry of the pencil beam spot profile) about the full 2D beam spot profile, thus making it possible to perform reconstructions of the 2D dose distribution.…”

“…The reconstruction of the 2D dose pattern from 1D projection measurements is generally not feasible due to degeneracy 38,39 . The characteristics of a modern proton PBS, however, allow for reasonable assumptions to be made to enable such reconstructions.…”

“…The reconstruction of the 2D dose pattern from 1D projection measurements is generally not feasible due to degeneracy. 38,39 The characteristics of a modern proton PBS, however, allow for reasonable assumptions to be made to enable such reconstructions. During the acceptance and commissioning of the ProBeam system, the optical asymmetry of the spots was fine-tuned to be less than 15%, with the difference of the spot sigma in the x-and y-directions measured to be within 3%.…”