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Optimizing Coded Aperture Imaging techniques to allow for online tracking of fiducial markers with high‐energy scattered radiation from treatment beam
Author(s) -
Mahl Adam,
Miller Brian,
Miften Moyed,
Jones Bernard L.
Publication year - 2020
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 - 10.1002/mp.14365
Subject(s) - fiducial marker , coded aperture , imaging phantom , optics , aperture (computer memory) , physics , centroid , collimated light , tracking (education) , dosimetry , detector , image guided radiation therapy , medical imaging , monte carlo method , nuclear medicine , computer science , computer vision , artificial intelligence , medicine , mathematics , acoustics , psychology , laser , pedagogy , statistics
Purpose Real‐time visualization of target motion using fiducial markers during radiation therapy treatment will allow for more accurate dose delivery. The purpose of this study was to optimize techniques for online fiducial marker tracking by detecting the scattered treatment beam through coded aperture imaging (CAI). Coded aperture imaging is a novel imaging technique that can allow target tracking in real time during treatment, and do so without adding any additional radiation dose, by making use of the scattered treatment beam radiation. Methods Radiotherapy beams of various energies, incident on phantoms containing gold fiducial markers were modeled using MCNP6.2 Monte Carlo transport code. Orthogonal scatter radiographs were collected through a CAI geometry. After decoding the simulated radiograph data, the centroid location and FWHM/SNR of the fiducial signals were analyzed. The effects of properties related to the CA (rank, pattern, and physical dimensions), detector (dimensions and pixel count), position (CA and phantom), and the incident beam (spectrum and direction) were investigated. These variables were evaluated by quantifying the positional accuracy, resolution, and SNR of the fiducials' signal. The effects of phantom scatter and decoding artifacts were reduced via Fourier filtering to avoid treatment interruption and physical interaction with the coded mask. Results The method was able to accurately localize the markers to within 1 pixel of a simulated radiograph. A 10 × 10 × 2 cm tungsten mask was chosen to attenuate >99 % of incident scatter through opaque elements, while minimizing collimation artifacts which arise from vignetting of the coded radiograph. Clear separation of centroids from fiducial signals with 2.5 mm separation was maintained, and initial optimization of parameters has produced an aperture which decodes the location of multiple fiducial markers inside a human phantom properly with a high SNR in the final radiograph image. Conclusion Current results show a proof of concept for a novel real‐time imaging method. Coded aperture imaging is a promising technique for extracting the fiducial scatter signal from a broader Compton‐scatter background. These results can be used to further optimize the CAI parameter space and guide fabrication and testing of a clinical device.