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CBCT with specification of imaging dose and CNR by anatomical volume of interest
Author(s) -
Leary Del,
Robar James L.
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 - 10.1118/1.4855835
Subject(s) - imaging phantom , collimated light , cone beam computed tomography , medical imaging , multileaf collimator , nuclear medicine , image guided radiation therapy , image quality , contrast to noise ratio , computer science , physics , optics , linear particle accelerator , medicine , beam (structure) , computer vision , artificial intelligence , computed tomography , image (mathematics) , radiology , laser
Purpose: A novel method has been developed for volume of interest (VOI) cone‐beam CT (CBCT) imaging using a 2.35 MV/Carbon target linac imaging beam line combined with dynamic multileaf collimator sequences.Methods: The authors demonstrate the concept of acquisition of multiple, separate imaging volumes, where volumes can be either completely separated or nested, and are associated with predetermined imaging dose and contrast‐to‐noise ratio (CNR) characteristics. Two individual MLC sequences were established in the planning system (Eclipse, Varian Medical) to collimate the beam according to a defined inner VOI (e.g., containing a target volume under image guidance) and an outer VOI (e.g., including surrounding landmarks or organs‐at‐risk). MLC sequences were interleaved as a function of gantry angle to produce a reconstructed CBCT image with nested VOIs. By controlling the ratio of inner‐to‐outer ratio of MLC segments (and thus Monitor Units) during acquisition, the relative dose and CNR in the two volumes can be controlled. Inner‐to‐outer ratios of 2:1 to 6:1 were examined.Results: The concept was explored using an anatomical head phantom to assess image quality. A geometric phantom was used to quantify absolute dose and CNR values for the various sequences. The authors found that the dose in the outer VOI decreased by a functional relationship dependent on the inner‐to‐outer sequence ratio, while the CNR varied by the square root of dose, as expected.Conclusions: In this study the authors demonstrate flexibility in VOI CBCT by tailoring the imaging dose and CNR distribution in separate volumes within the patient anatomy. This would allow for high quality imaging of a target volume for alignment purposes, with simultaneous low dose imaging of the surrounding anatomy (e.g., for coregistration).