Dimensional Cone-beam CT Research Articles

Do all the linear accelerators comply with the ICRU 91's constraints for stereotactic body radiation therapy treatments?

Recent technological developments in linear accelerators (linacs) and their imaging systems have made it possible to routinely perform stereotactic radiotherapy (SRT) treatments. To ensure the security and quality of the treatments, national and international recommendations have been written. This review focuses on the recommendations of the report 91 of the International Commission on Radiation Units (ICRU) on stereotactic treatments with small photon beams and proposes to answer the question of the eligibility of the commercially available accelerators for the treatment of extra-cranial SRT (SBRT). The ICRU 91 report outlines important features needed to respect the constraints, which are high intensity photon beam, integrated image-guidance, high mechanical accuracy of the linac, multileaf collimator with reduced leaf width, bundled motion management and bundled 6 Dimensional “robotic” couch tabletop. Most of the contemporary linacs meet these recommendations, in particular, stereotactic dedicated linacs, or modern gantry-based linacs equipped with 3 dimensional cone-beam CT imaging and 2D-stereoscopic planar imaging. Commercially available ring-based linacs have some limitations: they offer only coplanar treatments, and couch movements are limited to translations and, some have limited imaging equipment and no ability to manage intrafraction motion. However, for performing SBRT, non-coplanar irradiations are not mandatory, contrarily to intracranial stereotactic irradiations. Furthermore, patients’ rotations can be corrected, thanks to real-time adaptive radiotherapy available on MRI-linacs. Finally, significant improvements are expected in the short term to compensate the weaknesses of the current devices.

Three dimensional cone-beam CT sialography in non tumour salivary pathologies: procedure and results

Background: Three-dimensional cone-beam CT sialography (3D-CBCT sialography) tends to replace conventional sialography for exploring salivary gland diseases.

Real-time respiratory triggered four dimensional cone-beam CT halves imaging dose compared to conventional 4D CBCT

Four dimensional cone-beam computed tomography (4D CBCT) improves patient positioning and the accuracy of radiation therapy for patients with mobile tumours. Generally, 4D CBCT requires many hundreds of x-ray projections to measure target trajectories and the imaging frequency is not adapted to the patient’s respiratory signal resulting in over-sampling. In contrast, respiratory triggered 4D CBCT (RT 4D CBCT) is an acquisition technique that has been experimentally implemented and has shown to reduce the number of x-ray projections and thus 4D CBCT dose with minimal impact on image quality. The aim of this work is to experimentally investigate RT 4D CBCT in situ and measure target trajectory mean position, image quality and imaging dose from this approach. A commercially available phantom with programmable target motion was programmed with nine target trajectories derived from patient-measured respiratory traces known to span the range of image quality when used for 4D CBCT reconstruction. 4D CBCT datasets were acquired for each target trajectory using the RT 4D CBCT acquisition technique and the conventional 4D CBCT acquisition technique. From the reconstructed 4D CBCT datasets, target trajectory mean positions, imaging dose and image quality metrics were calculated and compared between the two techniques. Target trajectory and mean position were measured by tracking the target’s displacement in the phantom; imaging dose was measured by counting the total number of x-ray projections acquired; and image quality was assessed by calculating the contrast-to-noise ratio (CNR), signal-to-noise ration (SNR) and edge response width (ERW). For each of the nine cases, the target trajectory mean position as determined by RT 4D CBCT and conventional 4D CBCT varied from the reference source trajectory mean position by 0.7 mm or less except for one case where a conventional 4D CBCT mean position varied by 1.3 mm. On the average of these nine studies, RT 4D CBCT required half as many projections as conventional 4D CBCT giving a 50% reduction in imaging dose. Overall, the image quality metrics (CNR and SNR) were marginally worse for RT 4D CBCT; ERW metric showed no statistically significant difference between the RT 4D CBCT and conventional 4D CBCT reconstructed datasets. Respiratory triggered 4D CBCT couples the real-time respiratory signal to the 4D CBCT image acquisition system and requires less imaging dose than conventional 4D CBCT to determine target trajectory mean positions.

Volumetric Assessment of Mandibular Symphyseal Bone graft for Secondary Reconstruction of Unilateral Alveolar Clefts

Purpose: To evaluate the volume of bone graft that can be harvested from the mandibular symphysis and compare it with the bone volume needed for secondary grafting unilateral alveolar clefts using a computer-aided design (CAD) software program based on 3 Dimensional Cone Beam CT Scans. In addition, to study the bone fill of the mandibular symphysis graft in the alveolar cleft.Subjects & Methods: The subjects were 12 patients with unilateral alveolar clefts who underwent Cone Beam CT Scans 1 week prior to procedure. Using a 3D Analysis Software, the available bone that can be harvested from the mandibular symphysis area was determined using CBCT. Also, the volume of the Alveolar cleft defect was calculated preoperatively to assess the sufficiency of the symphyseal bone graft. All patients underwent secondary alveolar cleft grafting with mandibular symphysis bone. Six months postoperatively, CBCT was used to evaluate the amount of bone fill of the alveolar cleft.Results: The mean harvestable symphysis bone volume including the lingual cortex was 2.4 cm3 (range: 1.4–4.3 cm3). The actual harvested particulate symphyseal bone graft volume was calculated during surgery and was 2.62 cm3 (range: 1.6–4.0 cm3). The preoperative mean volume of the unilateral alveolar cleft defects was 1.9 cm3 (range: 1.1- 2.85 cm3). The mean postoperative bone fill ratio of the unilateral alveolar cleft was 79% (range 54% to 96%) 6 months postoperatively.Conclusion: This Study showed that the mandibular symphysis provided sufficient bone volume for secondary unilateral alveolar cleft grafting. Also, the mandibular symphyseal bone graft provided adequate bone fill of the alveolar cleft 6 months postoperatively..

Fast 4D cone-beam CT from 60 s acquisitions.

Background & purposeFour dimensional Cone beam CT (CBCT) has many potential benefits for radiotherapy but suffers from poor image quality, long acquisition times, and/or long reconstruction times. In this work we present a fast iterative reconstruction algorithm for 4D reconstruction of fast acquisition cone beam CT, as well as a new method for temporal regularization and compare to state of the art methods for 4D CBCT.Materials & methodsRegularization parameters for the iterative algorithms were found automatically via computer optimization on 60 s acquisitions using the XCAT phantom. Nineteen lung cancer patients were scanned with 60 s arcs using the onboard image on a Varian trilogy linear accelerator. Images were reconstructed using an accelerated ordered subset algorithm. A frequency based temporal regularization algorithm was developed and compared to the McKinnon-Bates algorithm, 4D total variation and prior images compressed sensing (PICCS).ResultsAll reconstructions were completed in 60 s or less. The proposed method provided a structural similarity of 0.915, compared with 0.786 for the classic McKinnon-bates method. For the patient study, it provided fewer image artefacts than PICCS, and better spatial resolution than 4D TV.ConclusionFour dimensional iterative CBCT reconstruction was done in less than 60 s, demonstrating the clinical feasibility. The frequency based method outperformed 4D total variation and PICCS on the simulated data, and for patients allowed for tumor location based on 60 s acquisitions, even for slowly breathing patients. It should thus be suitable for routine clinical use.

Visualization of Organ Motion Using Four Dimensional Cone-beam CT and Its Applications

Visualization of Organ Motion Using Four Dimensional Cone-beam CT and Its Applications

A new classification of mandibular asymmetry and evaluation of surgical-orthodontic treatment outcomes in Class III malocclusion.

Facial asymmetry is a common manifestation in patients with Class III malocclusion. The aims of this study were to classify mandibular asymmetry in Class III patients and to evaluate treatment outcomes according to different characteristics of asymmetry. Three dimensional cone-beam CT images of 38 patients were analyzed for menton deviation and discrepancies between bilateral structures of mandibular ramus and body. The patients were classified into 3 groups. Groups 1 and 2 exhibited a larger distance of ramus to midsagittal plane on menton-deviated side. In group 1, menton deviation was greater than ramus asymmetry and the condition was reversed for group 2. Group 3 had menton deviation contralateral to the side with larger transverse ramus distance. The features of asymmetry were delineated and the outcomes after surgical-orthodontic treatment were analyzed. Group 1 exhibited a roll rotation of mandibular structures. Mandibular deviation of group 2 patients was more of a horizontal shift nature rather than rotation. Group 3 patients displayed a yaw rotation of mandible to the side with lesser growth in body and ramus. After treatment, menton deviation and body asymmetry were significantly improved in all 3 groups, but the effect of therapy on ramus asymmetry was less predictable, especially for group 3. The classification system is simple and clinically useful and could form a base for future studies on facial asymmetry.

SU-E-I-14: Improvement of Four Dimensional Cone Beam CT Image Quality with Iterative Reconstruction

Purpose: Four‐dimensional cone beam CT (4D‐CBCT) is well known as powerful modality for image guided radiation therapy. Conventionally, it is reconstructed by sorting the X‐ray projection images into each respiratory phase according to a breathing signal using the FDK algorithm. This usually leads to inadequate number of projections in each phase, resulting in low quality 4D‐CBCT images with obvious streaking artifacts. We tried to improve the image quality for 4D CBCT using iterative reconstruction method (ML‐convex) and compared with the images by FDK in SNR of the reconstructed images. Methods: We used ML‐convex algorithm, which has the ability to reconstruct CBCT images from a few number of noisy x‐ray projections by taking knowledge of x‐ray photon statistics into account. We compared the image quality of 4D CBCT by ML‐convex with that by FDK using projection images acquired with different rotational speeds by XVI 5.0 (Elekta). Projection images were sorted by 10 phases for both reconstruction algorithms. A phantom study and patient study were performed. The convergence rate and reconstruction accuracy were evaluated using Catphan‐600 physical phantom. Results: Image quality of 4D‐CBCT is substantially enhanced by the ML‐convex algorithm. Streaking artifacts, commonly presented in the image reconstructed by FDK algorithm, are almost suppressed in spite of the small number of projections. Quantitative evaluations indicated that, compared with the FDK results, ML‐convex method improves signal‐to‐noise‐ratio (SNR) and reconstructed more accurate CT value. Conclusion: The ML‐convex algorithm yielded images with higher SNR and more accurate CT value than those produced by FDK algorithm. This Result will enable us to apply 4D CBCT by ML‐convex algorithm to Image Guided Adaptive Radiation Therapy and patient daily CBCT‐based treatment localization in real clinical environments with the higher computational efficiency.

PD-0411: Improvement of four dimensional cone beam CT image quality with iterative reconstruction

PD-0411: Improvement of four dimensional cone beam CT image quality with iterative reconstruction

Three dimensional cone-beam CT study of upper airway change after mandibular setback surgery for skeletal Class III malocclusion patients

Three dimensional cone-beam CT study of upper airway change after mandibular setback surgery for skeletal Class III malocclusion patients

O-151 Four dimensional cone beam CT for verification of radiotherapy for lung cancer

O-151 Four dimensional cone beam CT for verification of radiotherapy for lung cancer