Four‐dimensional cone‐beam computed tomography using an on‐board imager

Abstract

On-board cone-beam computed tomography (CBCT) has recently become available to provide volumetric information of a patient in the treatment position, and holds promises for improved target localization and irradiation dose verification. The design of currently available on-board CBCT, however, is far from optimal. Its quality is adversely influenced by many factors, such as scatter, beam hardening, and intra-scanning organ motion. In this work we quantitatively study the influence of organ motion on CBCT imaging and investigate a strategy to acquire high quality phase-resolved [four-dimensional (4D)] CBCT images based on phase binning of the CBCT projection data. An efficient and robust method for binning CBCT data according to the patient's respiratory phase derived in the projection space was developed. The phase-binned projections were reconstructed using the conventional Feldkamp algorithm to yield 4D CBCT images. Both phantom and patient studies were carried out to validate the technique and to optimize the 4D CBCT data acquisition protocol. Several factors that are important to the clinical implementation of the technique, such as the image quality, scanning time, number of projections, and radiation dose, were analyzed for various scanning schemes. The general references drawn from this study are: (i) reliable phase binning of CBCT projections is accomplishable with the aid of external or internal marker and simple analysis of its trace in the projection space, and (ii) artifact-free 4D CBCT images can be obtained without increasing the patient radiation dose as compared to the current 3D CBCT scan.

Difference in performance between 3D and 4D CBCT for lung imaging: a dose and image quality analysis

“…Within this context, the common metric of contrast‐to‐noise ratio (CNR) may not be suitable, in the sense that a high CNR output may not indicate a better image quality (19) . To quantitatively assess the loss of image quality due to motion for the two imaging protocols, we chose to use CTF and NEQ metrics, eliminating any dependency of contrast measurement on the sample size and shape.…”

Evaluating the four-dimensional cone beam computed tomography with varying gantry rotation speed

“…[22][23][24] There are two methods discussed for reducing the angular spacing in 4DCBCT; one uses multiple rotations around the patient with normal gantry speed, 22,23 and the other uses reduced gantry speed (slow rotation). [23][24][25] It has been concluded that the slower gantry rotation produces superior 4DCBCT images compared with multiple gantry rotation since the multiple gantry rotation method may miss or duplicate projections.…”

“…Recently, the time synchronized CBCT (4DCBCT) method has been introduced to manage respiration-induced target motion during treatment verification imaging. [22][23][24][25][26][27][28][29][30] In 4DCBCT imaging, two-dimensional (2D) projections acquired at different times and positions are sorted into several groups, according to their respiratory phases, and each phase group is then reconstructed independently to obtain a volumetric image corresponding to that specific phase. The respiratory wave required for retrospective 4DCBCT reconstructions is derived using either 2D projections of CBCT itself or an external surrogate system.…”

Imaged-guided liver stereotactic body radiotherapy using VMAT and real-time adaptive tumor gating. Concerns about technique and preliminary clinical results

“…), in most cases for a pre-treatment set-up. [14][15][16][17][18] But those approaches have some inconvenient, leading to possible target miss. First, due to the fact that they are associated with external information not directly correlated to the tumor motion; and second, because of the impossibility to asses changes in the amplitude of breathing motion that may occur during some fractions, using only pretreatment imaging verification.…”