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SU‐E‐I‐01: A Fast, Analytical Pencil Beam Based Method for First Order X‐Ray Scatter Estimation of Kilovoltage Cone Beam X‐Rays
Author(s) -
Liu J,
Bourland J
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4887949
Subject(s) - physics , imaging phantom , monte carlo method , optics , scattering , photon , ray tracing (physics) , attenuation , pencil (optics) , beam (structure) , computational physics , mathematics , statistics
Purpose: To analytically estimate first‐order x‐ray scatter for kV cone beam x‐ray imaging with high computational efficiency. Methods: In calculating first‐order scatter using the Klein‐Nishina formula, we found that by integrating the point‐to‐point scatter along an interaction line, a “pencil‐beam” scatter kernel (BSK) can be approximated to a quartic expression when the imaging field is small. This BSK model for monoenergetic, 100keV x‐rays has been verified on homogeneous cube and cylinder water phantoms by comparing with the exact implementation of KN formula. For heterogeneous medium, the water‐equivalent length of a BSK was acquired with an improved Siddon's ray‐tracing algorithm, which was also used in calculating pre‐ and post‐ scattering attenuation. To include the electron binding effect for scattering of low‐kV photons, the mean corresponding scattering angle is determined from the effective point of scattered photons of a BSK. The behavior of polyenergetic x‐rays was also investigated for 120kV x‐rays incident to a sandwiched infinite heterogeneous slab phantom, with the electron binding effect incorporated. Exact computation and Monte Carlo simulations were performed for comparisons, using the EGSnrc code package. Results: By reducing the 3D volumetric target (o(n 3 )) to 2D pencil‐beams (o(n 2 )), the computation expense can be generally lowered by n times, which our experience verifies. The scatter distribution on a flat detector shows high agreement between the analytic BSK model and exact calculations. The pixel‐to‐pixel differences are within (‐2%, 2%) for the homogeneous cube and cylinder phantoms and within (0, 6%) for the heterogeneous slab phantom. However, the Monte Carlo simulation shows increased deviation of the BSK model toward detector periphery. Conclusion: The proposed BSK model, accommodating polyenergetic x‐rays and electron binding effect at low kV, shows great potential in efficiently estimating the first‐order scatter from small imaging fields. We are investigating more thoroughly to improve performance and explore applications.