Cone Beam Digital Tomosynthesis Research Articles

Cone-beam digital tomosynthesis for thin slab objects

We describe a cone-beam computed tomography with insufficient projections obtained from a limited angle scan, the so-called cone-beam digital tomosynthesis. Digital tomosynthesis produces cross-sectional images parallel to the axis of rotation from a series of projection images acquired from a planar detector. The image reconstruction algorithm is based on the cone-beam filtered backprojection method. To suppress the out-of-plane artifacts due to the incomplete sampling over a limited angular range, we applied an apodizing filter in the depth direction. We applied the digital tomosynthesis technique to a multilayer printed circuit board possessing thin slab geometry and evaluated its performance with respect to various operation parameters, such as the total scan angle, the step angle and the number of projection images used for reconstruction. The results showed that the image quality of digital tomosynthesis reconstructed for the total scan angle greater than 60 degrees with a step angle as narrow as possible exhibited that it was comparable to that of the computed tomography. The digital tomosynthesis technique is expected to be practical for extracting internal cross-sectional views, parallel to the scan direction, of objects with thin slab geometry.

DART, a platform for the creation and registration of cone beam digital tomosynthesis datasets

Digital tomosynthesis is an imaging modality that allows for tomographic reconstructions using only a fraction of the images needed for CT reconstruction. Since it offers the advantages of tomographic images with a smaller imaging dose delivered to the patient, the technique offers much promise for use in patient positioning prior to radiation delivery. This paper describes a software environment developed to help in the creation of digital tomosynthesis image sets from digital portal images using three different reconstruction algorithms. The software then allows for use of the tomograms for patient positioning or for dose recalculation if shifts are not applied, possibly as part of an adaptive radiotherapy regimen.

High-DQE EPIDs based on thick, segmented BGO and CsI:Tl scintillators: performance evaluation at extremely low dose.

Electronic portal imaging devices (EPIDs) based on active matrix, flat-panel imagers (AMFPIs) have become the gold standard for portal imaging and are currently being investigated for megavoltage cone-beam computed tomography (CBCT) and cone-beam digital tomosynthesis (CBDT). However, the practical realization of such volumetric imaging techniques is constrained by the relatively low detective quantum efficiency (DQE) of AMFPI-based EPIDs at radiotherapy energies, approximately 1% at 6 MV. In order to significantly improve DQE, the authors are investigating thick, segmented scintillators, consisting of 2D matrices of scintillating crystals separated by septal walls. A newly constructed segmented BGO scintillator (11.3 mm thick) and three segmented CsI:Tl scintillators (11.4, 25.6, and 40.0 mm thick) were evaluated using a 6 MV photon beam. X-ray sensitivity, modulation transfer function, noise power spectrum, DQE, and phantom images were obtained using prototype EPIDs based on the four scintillators. The BGO and CsI:Tl prototypes were found to exhibit improvement in DQE ranging from approximately 12 to 25 times that of a conventional AMFPI-based EPID at zero spatial frequency. All four prototype EPIDs provide significantly improved contrast resolution at extremely low doses, extending down to a single beam pulse. In particular, the BGO prototype provides contrast resolution comparable to that of the conventional EPID, but at 20 times less dose, with spatial resolution sufficient for identifying the boundaries of low-contrast objects. For this prototype, however, the BGO scintillator exhibited an undesirable radiation-induced variation in x-ray sensitivity. Prototype EPIDs based on thick, segmented BGO and CsI:T1 scintillators provide significantly improved portal imaging performance at extremely low dose (i.e., down to 1 beam pulse corresponding to approximately 0.022 cGy), creating the possibility of soft-tissue visualization using MV CBCT and CBDT at clinically practical dose.

On-board CBCT/CBDT for Image-guided Proton Therapy: Initial Performance Evaluation

Currently, only two orthogonal x-ray projections are used to register position of patient at treatment with that of radiation therapy planning (RTP). If tomograms of a patient can be directly acquired in the treatment room, it is possible to compare with the CT data of RTP, which gives us much more accurate registration results than the orthogonal alignment system. The purpose is to investigate the feasibility of CBCT (cone beam CT) and CBDT (cone beam digital tomosynthesis) methods in the treatment room for accurately aligning the patient in the proton beam.

SU-FF-J-86: A Digital Tomosynthesis Applications in Radiotherapy Toolkit

Purpose: To develop a toolkit to allow for the creation of cone-beam digital tomosynthesis datasets and their registration to determine patient shifts before treatment delivery. Method and Materials: The Matlab and visual C++ platforms were utilized to create a user interface that allows for the use of megavoltage portal images to reconstruct digital tomosynthesis datasets via one of three reconstruction algorithms. The software also allows for the use of digitally reconstructed radiographs from a CT dataset to reconstruct a reference tomosynthesis image set for registration purposes. To benchmark the software, a phantom study was created where known shifts were introduced in a phantom's position before portal images were acquired. The portal images were used to reconstruct tomosynthesis-based datasets with one of the three algorithms. These were then compared against the reference image set. Results: The software allowed for the quick reconstruction of digital tomosynthesis datasets. Once the registration was performed, all the calculated parameters to shift the phantom back to its original position showed close agreement with the actual shifts introduced in the phantom before images were acquired. Conclusion: Based on the benchmarking experiment performed on this software toolkit, it seems like the program is performing all of its tasks correctly. The small deviations found between the registration results and the actual shifts introduced to the phantom may be due to the subjectivity of the user who performed the registration since it was performed manually.

Characteristics of megavoltage cone‐beam digital tomosynthesis

This article reports on the image characteristics of megavoltage cone-beam digital tomosynthesis (MVCB DT). MVCB DT is an in-room imaging technique, which enables the reconstruction of several two-dimensional slices from a set of projection images acquired over an arc of 20 degrees-40 degrees. The limited angular range reduces the acquisition time and the dose delivered to the patient, but affects the image quality of the reconstructed tomograms. Image characteristics (slice thickness, shape distortion, and contrast-to-noise ratio) are studied as a function of the angular range. Potential clinical applications include patient setup and the development of breath holding techniques for gated imaging.

Megavoltage cone beam digital tomosynthesis (MV-CBDT) for image-guided radiotherapy: a clinical investigational system

Cone beam digital tomosynthesis (CBDT) is a new imaging technique proposed recently as a rapid approach for creating tomographic images of a patient in the radiotherapy treatment room. The purpose of this work is to investigate the feasibility of performing megavoltage (MV) CBDT clinically. A clinical investigational MV-CBDT system was installed on an existing LINAC. After the installation, the treatment machine can be operated in two distinct modes: (1) normal clinical treatment mode; (2) CBDT mode, in which tomographic images of the patient can be obtained using MV-CBDT. Various calibration and phantom measurements were performed on the system, followed by a patient study. Our phantom measurements have shown that: (1) for the same imaging dose, MV-CBDT has the same signal-difference-to-noise ratio as megavoltage cone beam computed tomography (MV-CBCT); (2) MV-CBDT has a better spatial resolution than MV-CBCT in the planes of reconstruction but a worse spatial resolution in the direction perpendicular to the planes of reconstruction. MV-CBDT patient images were also obtained and compared to that of MV-CBCT. We have demonstrated that it is clinically feasible to perform MV-CBDT in the treatment room for image-guided radiotherapy.

Megavoltage Cone Beam Digital Tomosynthesis in Target Volume Localization for Patients Undergoing Prostate External Beam Radiotherapy: A Novel Method of IGRT

Megavoltage Cone Beam Digital Tomosynthesis in Target Volume Localization for Patients Undergoing Prostate External Beam Radiotherapy: A Novel Method of IGRT

Lag correction model and ghosting analysis for an indirect‐conversion flat‐panel imager

Cone‐beam digital tomosynthesis (CBDT) is a new approach that was recently proposed for rapid tomographic imaging of soft‐tissue targets in the radiotherapy treatment room. One of the potential problems in implementing CBDT using, for example, megavoltage (MV) X rays is the possibility of artifacts caused by image lag and ghosting of the X‐ray detector used. In the present work, we developed a model to correct for image lag with indirect‐conversion flat‐panel imagers (FPIs) used for MV‐CBDT. This model is based on measurement and analysis of image lag in an indirect‐conversion FPI irradiated with a 6‐MV X‐ray beam. Our results demonstrated that image lag is amenable to correction. In addition, we measured the ghosting effect for an indirect‐conversion FPI and found it to be insignificant.PACS numbers: 87.53.Oq, 87.57.Ce

SU‐DD‐A3‐04: Quantitative Evaluation of Cone Beam Digital Tomosynthesis (CBDT) for Image‐Guided Radiation Therapy

Purpose: Cone beam digital tomosynthesis (CBDT) is a new imaging technique proposed by us recently as a rapid approach for creating cross sectional images of a patient in the radiotherapy treatment room. Similar to the cone beam computed tomography (CBCT) approach, the CBDT uses an X‐ray source and an X‐ray detector on a Linac to acquire projection data by rotation around the patient. Unlike CBCT, CBDT utilizes partial scans, typically in the range of 20–60 degrees of gantry arc. The purposes of this work are (1) to evaluate quantitatively the image quality of CBDT in terms of signal‐to‐noise ratio and spatial resolution; (2) to demonstrate that we can use CBDT to image soft tissue targets, e.g., the prostate. Method and Materials: An experimental CBDT system has been built on a Linac with a recently developed flat‐panel detector. A number of phantoms including a spatial resolution phantom, two contrast‐detail phantoms and a custom‐made anthropomorphic pelvic phantom (CIRS Inc.) were used in the evaluation. CBDT phantom images have been generated and analyzed for different degrees of gantry arc and compared to those from CBCT. Results: Quantitative results on signal‐to‐noise ratio and spatial resolution have been obtained for different degrees of gantry arc. Compared to CBCT, CBDT has a worse spatial resolution in the direction perpendicular to the planes of reconstruction but a better resolution in the parallel direction. The image quality of CBDT is acceptable in the planes most relevant to the treatment. It has been shown that the prostate is visible on CBDT reconstructed images of the pelvic phantom. Conclusion: This work indicates that the CBDT approach can be a viable and rapid tomographical imaging technique for treatment verification in radiotherapy. Conflict of Interest: This work was partially supported by Siemens Medical Solutions, Inc.

TH‐D‐ValB‐05: Evaluation of Image Quality in Megavoltage Digital Tomosynthesis

Purpose: We report on the characteristics of Megavoltage Cone Beam Digital Tomosynthesis (MVCB DTS) and its potential clinical application for imaging of pulmonary lesions. Method and Materials: MVCB CT refers to the reconstruction of a 3D image from a set of 2D projections, acquired using a medical linear accelerator equipped with an electronic portal imaging device (EPID). A typical MVCB CT scan is acquired over a 200 degrees arc. In the case of MVCB DTS, the angular range is limited to reduce the acquisition time. This limited angular range affects the image quality of the reconstructed tomograms. To study the image quality as a function of the angular range, phantom measurements were performed and data from a head and neck patient were analyzed. The image quality was analyzed in terms of effective slice thickness, shape distortion and contrast sensitivity. MVCB DTS of the lung was performed on patients, with localized and diffuse lesions. Results: The image quality and the capability to distinguish overlaid structures decreases with decreasing angular range: a 20 degrees arc DTS results in a slice thickness of 2.7cm (vs. 1mm), a ratio of the vertical to lateral diameter of a sphere of 0.15, and a reduced contrast sensitivity. The acquisition is faster than MVCB CT. It takes 5–10 seconds for arcs of 20–40 degrees, compared to 45 seconds for a 200 degrees arc. In lung images, the faster acquisition results in a reduced blur due to the respiratory motion. Conclusion: This study indicates some potential advantages of DTS for imaging lung patients in the treatment position. Compared with EPID, DTS provides 3D information and better soft tissue contrast. Compared with CBCT, DTS allows shorter acquisition times, compatible with breath holding.Conflict of Interest: Research sponsored by Siemens OCS.

WE‐C‐J‐6C‐09: Cone Beam Digital Tomosynthesis (CBDT): An Alternative to Cone Beam Computed Tomography (CBCT) for Image‐Guided Radiation Therapy

Purpose: To investigate the feasibility of using a new imaging technique, i.e., Cone Beam Digital Tomosynthesis (CBDT) as an alternative to the Cone Beam Computed Tomography (CBCT) approach for creating 3D cross sectional images of a patient in the radiotherapy treatment room. Method and Materials: Similar to the CBCT approach, the CBDT uses an x‐ray source (either a kV source or a MV source on a Linac or another radiation‐emitting device) and an x‐ray detector to acquire projection data by rotating them around a patient simultaneously. Unlike CBCT, CBDT utilizes partial scans, typically in the range of 20–60 degrees of gantry arc. The main advantage of the CBDT approach is that it takes less time to perform image acquisition and reconstruction. An experimental CBDT system has been built on a Linac with a recently developed flat‐panel detector. A novel filtered backprojection algorithm was developed for CBDT reconstructions. CBDT phantom images have been generated for different degrees of gantry arc and beamline configurations and compared to those from CBCT. Results: Cross‐sectional images of a Rando phantom were generated with comparable image quality to CBCT using as small as ∼ 22 degree gantry arc. The planes of CBDT reconstruction are orthogonal to the x‐ray beam at the midpoint of the arc. These reconstructed planes are of particular relevance to image‐guided radiation therapy, because they depict anatomy along planes that are most relevant to the treatment beam, i.e., orthogonal to the beam axis. Conclusion: We have demonstrated the feasibility of using CBDT to acquire cross‐sectional images of an object in the treatment room to guide radiotherapy treatment. Compared to CBCT, the CBDT approach is much faster with acceptable image quality in the planes most relevant to the treatment. Conflict of Interest: This work was supported by Siemens Medical Solutions USA, Inc.

TH-C-J-6B-10: 4D Cone Beam Digital Tomosynthesis (CBDT) and Digitally Reconstructed Tomograms (DRTs) for Improved Image Guidance of Lung Radiotherapy

Purpose: The purpose of this work is to devise an efficient, effective and routine imaging modality to guide lungradiotherapy. Current methods involve acquiring a 4D‐CBCT and comparing the digitally reconstructedradiographs (DRRs) for multiple breathing phases with online fluoroscopic images. A major shortcoming of DRRs and fluoroscopy is that unwanted structures such as bones occlude the target. Furthermore 4D‐CBCT requires long acquisition times and large patient dose, making it impractical for routine use. Method and Materials: We propose a partial arc cone beam acquisition, which we call “cone beam digital tomosynthesis” (CBDT), to obtain cross‐sectional images of a slab just thick enough to enclose the soft tissue target. Projections through this slab make “digitally reconstructed tomograms” (DRTs). Similar to DRRs, DRTs correct for beam divergence. However, different from DRRs, DRTs do not contain irrelevant structures outside the slab, making the target far more conspicuous. By gating this acquisition, dynamic cross sections and DRTs are obtained at multiple respiratory phases. These dynamic images are registered with those obtained from the planning 4D‐CT dataset to guide treatment. Results: The DRRs constructed from multiple phases of a 4D‐CT emphasize bony anatomy and other irrelevant structures overlaying the target, making the edges of the target difficult to find. We have demonstrated that this difficulty is overcome by the use of cross‐sectional images from CBDT and DRTs, which are obtained with an image acquisition time that is significantly shorter than full‐volume 4D‐CBCT. Matching DRTs were obtained from the planning 4D‐CT for each phase. 2D‐2D registrations were performed to obtain the phase‐varying offset. Conclusion: A new imaging technique has been introduced for image‐guidedlung treatment. With this approach, images are acquired faster and the appearance of the tumor is significantly enhanced by eliminating many extraneous structures. Conflict of Interest: This work is supported by Siemens.