Image guidance in radiation therapy for better cure of cancer

The key goal and main challenge of radiation therapy is the elimination of tumors without any concurring damages of the surrounding healthy tissues and organs. Radiation doses required to achieve sufficient cancer‐cell kill exceed in most clinical situations the dose that can be tolerated by the healthy tissues, especially when large parts of the affected organ are irradiated. High‐precision radiation oncology aims at optimizing tumor coverage, while sparing normal tissues. Medical imaging during the preparation phase, as well as in the treatment room for localization of the tumor and directing the beam, referred to as image‐guided radiotherapy (IGRT), is the cornerstone of precision radiation oncology. Sophisticated high‐resolution real‐time IGRT using X‐rays, computer tomography, magnetic resonance imaging, or ultrasound, enables delivery of high radiation doses to tumors without significant damage of healthy organs. IGRT is the most convincing success story of radiation oncology over the last decades, and it remains a major driving force of innovation, contributing to the development of personalized oncology, for example, through the use of real‐time imaging biomarkers for individualized dose delivery.

Cone-beam CT-derived relative stopping power map generation via deep learning for proton radiotherapy

PURPOSE

In intensity-modulated proton therapy (IMPT), protons are used to deliver highly conformal dose distributions, targeting tumors, and sparing organs-at-risk. However, due to uncertainties in both patient setup and relative stopping power (RSP) calculation, margins are added to the treatment volume during treatment planning, leading to higher doses to normal tissues. Cone-beam computed tomography (CBCT) images are taken daily before treatment; however, the poor image quality of CBCT limits the use of these images for online dose calculation. In this work, we use a deep-learning-based method to predict RSP maps from daily CBCT images, allowing for online dose calculation in a step toward adaptive radiation therapy.

METHODS

Twenty-three head-and-neck cancer patients were simulated using a Siemens TwinBeam dual-energy CT (DECT) scanner. Mixed-energy scans (equivalent to a 120 kVp single-energy CT scan) were converted to RSP maps for treatment planning. Cone-beam computed tomography images were taken on the first day of treatment, and the planning RSP maps were registered to these images. A deep learning network based on a cycle-GAN architecture, relying on a compound loss function designed for structural and contrast preservation, was then trained to create an RSP map from a CBCT image. Leave-one-out and holdout cross validations were used for evaluation, and mean absolute error (MAE), mean error (ME), peak signal-to-noise ratio (PSNR), and structural similarity (SSIM) were used to quantify the differences between the CT-based and CBCT-based RSP maps. The proposed method was compared to a deformable image registration-based method which was taken as the ground truth and two other deep learning methods. For one patient who underwent resimulation, the new planning RSP maps and CBCT images were used for further evaluation and validation.

RESULTS

The CBCT-based RSP generation method was evaluated on 23 head-and-neck cancer patients. From leave-one-out testing, the MAE between CT-based and CBCT-based RSP was 0.06 ± 0.01 and the ME was -0.01 ± 0.01. The proposed method statistically outperformed the comparison DL methods in terms of MAE and ME when compared to the planning CT. In terms of dose comparison, the mean gamma passing rate at 3%/3 mm was 94% when three-dimensional (3D) gamma index was calculated per plan and 96% when gamma index was calculated per field.

CONCLUSIONS

The proposed method provides sufficiently accurate RSP map generation from CBCT images, allowing for evaluation of daily dose based on CBCT and possibly allowing for CBCT-guided adaptive treatment planning for IMPT.

Cone-beam CT for imaging of the head/brain: Development and assessment of scanner prototype and reconstruction algorithms

PURPOSE

Our aim was to develop a high-quality, mobile cone-beam computed tomography (CBCT) scanner for point-of-care detection and monitoring of low-contrast, soft-tissue abnormalities in the head/brain, such as acute intracranial hemorrhage (ICH). This work presents an integrated framework of hardware and algorithmic advances for improving soft-tissue contrast resolution and evaluation of its technical performance with human subjects.

METHODS

Four configurations of a CBCT scanner prototype were designed and implemented to investigate key aspects of hardware (including system geometry, antiscatter grid, bowtie filter) and technique protocols. An integrated software pipeline (c.f., a serial cascade of algorithms) was developed for artifact correction (image lag, glare, beam hardening and x-ray scatter), motion compensation, and three-dimensional image (3D) reconstruction [penalized weighted least squares (PWLS), with a hardware-specific statistical noise model]. The PWLS method was extended in this work to accommodate multiple, independently moving regions with different resolution (to address both motion compensation and image truncation). Imaging performance was evaluated quantitatively and qualitatively with 41 human subjects in the neurosciences critical care unit (NCCU) at our institution.

RESULTS

The progression of four scanner configurations exhibited systematic improvement in the quality of raw data by variations in system geometry (source-detector distance), antiscatter grid, and bowtie filter. Quantitative assessment of CBCT images in 41 subjects demonstrated: ~70% reduction in image nonuniformity with artifact correction methods (lag, glare, beam hardening, and scatter); ~40% reduction in motion-induced streak artifacts via the multi-motion compensation method; and ~15% improvement in soft-tissue contrast-to-noise ratio (CNR) for PWLS compared to filtered backprojection (FBP) at matched resolution. Each of these components was important to improve contrast resolution for point-of-care cranial imaging.

CONCLUSIONS

This work presents the first application of a high-quality, point-of-care CBCT system for imaging of the head/ brain in a neurological critical care setting. Hardware configuration iterations and an integrated software pipeline for artifacts correction and PWLS reconstruction mitigated artifacts and noise to achieve image quality that could be valuable for point-of-care detection and monitoring of a variety of intracranial abnormalities, including ICH and hydrocephalus.

Pelvic multi-organ segmentation on cone-beam CT for prostate adaptive radiotherapy

BACKGROUND AND PURPOSE

The purpose of this study is to develop a deep learning-based approach to simultaneously segment five pelvic organs including prostate, bladder, rectum, left and right femoral heads on cone-beam CT (CBCT), as required elements for prostate adaptive radiotherapy planning.

MATERIALS AND METHODS

We propose to utilize both CBCT and CBCT-based synthetic MRI (sMRI) for the segmentation of soft tissue and bony structures, as they provide complementary information for pelvic organ segmentation. CBCT images have superior bony structure contrast and sMRIs have superior soft tissue contrast. Prior to segmentation, sMRI was generated using a cycle-consistent adversarial networks (CycleGAN), which was trained using paired CBCT-MR images. To combine the advantages of both CBCT and sMRI, we developed a cross-modality attention pyramid network with late feature fusion. Our method processes CBCT and sMRI inputs separately to extract CBCT-specific and sMRI-specific features prior to combining them in a late-fusion network for final segmentation. The network was trained and tested using 100 patients' datasets, with each dataset including the CBCT and manual physician contours. For comparison, we trained another two networks with different network inputs and architectures. The segmentation results were compared to manual contours for evaluations.

RESULTS

For the proposed method, dice similarity coefficients and mean surface distances between the segmentation results and the ground truth were 0.96 ± 0.03, 0.65 ± 0.67 mm; 0.91 ± 0.08, 0.93 ± 0.96 mm; 0.93 ± 0.04, 0.72 ± 0.61 mm; 0.95 ± 0.05, 1.05 ± 1.40 mm; and 0.95 ± 0.05, 1.08 ± 1.48 mm for bladder, prostate, rectum, left and right femoral heads, respectively. As compared to the other two competing methods, our method has shown superior performance in terms of the segmentation accuracy.

CONCLUSION

We developed a deep learning-based segmentation method to rapidly and accurately segment five pelvic organs simultaneously from daily CBCTs. The proposed method could be used in the clinic to support rapid target and organs-at-risk contouring for prostate adaptive radiation therapy.

Synthetic CT generation from CBCT images via deep learning

PURPOSE

Cone-beam computed tomography (CBCT) scanning is used daily or weekly (i.e., on-treatment CBCT) for accurate patient setup in image-guided radiotherapy. However, inaccuracy of CT numbers prevents CBCT from performing advanced tasks such as dose calculation and treatment planning. Motivated by the promising performance of deep learning in medical imaging, we propose a deep U-net-based approach that synthesizes CT-like images with accurate numbers from planning CT, while keeping the same anatomical structure as on-treatment CBCT.

METHODS

We formulated the CT synthesis problem under a deep learning framework, where a deep U-net architecture was used to take advantage of the anatomical structure of on-treatment CBCT and image intensity information of planning CT. U-net was chosen because it exploits both global and local features in the image spatial domain, matching our task to suppress global scattering artifacts and local artifacts such as noise in CBCT. To train the synthetic CT generation U-net (sCTU-net), we include on-treatment CBCT and initial planning CT of 37 patients (30 for training, seven for validation) as the input. Additional replanning CT images acquired on the same day as CBCT after deformable registration are utilized as the corresponding reference. To demonstrate the effectiveness of the proposed sCTU-net, we use another seven independent patient cases (560 slices) for testing.

RESULTS

We quantitatively compared the resulting synthetic CT (sCT) with the original CBCT image using deformed same-day pCT images as reference. The averaged accuracy measured by mean absolute error (MAE) between sCT and reference CT (rCT) on testing data is 18.98 HU, while MAE between CBCT and rCT is 44.38 HU.

CONCLUSIONS

The proposed sCTU-net can synthesize CT-quality images with accurate CT numbers from on-treatment CBCT and planning CT. This potentially enables advanced CBCT applications for adaptive treatment planning.

Using Meglumine Diatrizoate to improve the accuracy of diagnosis of cracked teeth on Cone-beam CT images

AIM

To explore in a laboratory setting the feasibility of using Meglumine Diatrizoate (MD) to improve the accuracy of diagnosis of cracked teeth on cone-beam CT (CBCT) images.

METHODOLOGY

Twenty-four teeth were cracked artificially by soaking them cyclically in liquid nitrogen and hot water. The number and position of crack lines were evaluated with a dental operating microscope and used as the gold standard. The artificially cracked teeth were then examined using routine scanning (RS) and enhanced scanning (ES) modes, respectively. For the ES mode, MD was painted on the surface of the crack lines, and then, CBCT scanning with the same parameters was performed after 10 min. A radiological graduate student and an experienced radiologist evaluated the presence or absence of crack lines, respectively. The differences between the RS and ES modes were determined and assessed using McNemar's test. Inter-examiner agreement and intra-examiner agreement were assessed using kappa analysis.

RESULTS

Fifty-seven crack lines were found in the 24 cracked teeth. In the RS mode, the accuracy of detection of crack lines was 23% (radiological graduate student) and 32% (experienced radiologist), whereas in the ES mode, the accuracy was 61% (radiological graduate student) and 65% (experienced radiologist). The inter-examiner agreement was 0.693 in RS mode and 0.849 in ES mode. The intra-examiner agreement was 0.872 and 0.949 for the radiological graduate student in RS and ES mode respectively; and one for the experienced radiologist both in RS and ES mode.

CONCLUSIONS

Compared with routine scanning mode, more crack lines could be detected in enhanced scanning mode using Meglumine Diatrizoate as a contrast medium. MD could be a potential contrast medium to improve the accuracy of detection of crack lines on CBCT images.

Evaluating an Image-Guided Operating Room with Cone Beam CT for Skull Base Surgery

Importance  Skull base surgery requires precise preoperative assessment and intraoperative management of the patient. Surgical navigation is routinely used for complex skull base cases; however, the image guidance is commonly based on preoperative scans alone. Objective  The primary objective of this study was to assess the image quality of intraoperative cone-beam computed tomography (CBCT) within anatomical landmarks used in sinus and skull base surgery. The secondary objective was to assess the registration error of a surgical navigation system based on intraoperative CBCT. Design  Present study is a retrospective case series of image quality after intraoperative cone beam CT. Setting  The study was conducted at Toronto General Hospital and Princess Margaret Cancer Centre, University Health Network, Toronto. Participants  A total of 46 intraoperative scans (34 patients, 21 skull base, 13 head and neck) were studied. Main Outcome and Measures  Thirty anatomical landmarks (vascular, soft tissue, and bony) within the sinuses and anterior skull base were evaluated for general image quality characteristics: (1) bony detail visualization; (2) soft-tissue visualization; (3) vascular visualization; and (4) freedom from artifacts (e.g., metal). Levels of intravenous (IV) contrast enhancement were quantified in Hounsfield's units (HU). Standard paired-point registration between imaging and tracker coordinates was performed using 6 to 8 skin fiducial markers and the corresponding fiducial registration error (FRE) was measured. Results  Median score for bony detail on CBCT was 5, remaining at 5 after administration of IV contrast. Median soft-tissue score was 2 for both pre- and postcontrast. Median vascular score was 1 precontrast and 3 postcontrast. Median score for artifacts on CBCT were 2 for both pre-and postcontrast, and metal objects were noted to be the most significant source of artifact. Intraoperative CBCT allowed preresection images and immediate postresection images to be available to the skull base surgeon. There was a significant improvement in mean (standard deviation [SD]) CT intensity in the left carotid artery postcontrast 334 HU (67 HU) ( p  < 10 ^-10 ). The mean FRE was 1.8 mm (0.45 mm). Conclusion  Intraoperative CBCT in complex skull base procedures provides high-resolution bony detail allowing immediate assessment of complex resections. The use of IV contrast with CBCT improves the visualization of vasculature. Image-guidance based on CBCT yields registration errors consistent with standard techniques.

Projection-domain metal artifact correction using a dual layer detector

Metal artifact remains a challenge in cone-beam CT images. Many two-pass metal artifact reduction methods have been proposed, which work fairly well, but are limited when the metal is outside the scan field-of-view (FOV) or when the metal is moving during the scan. In the former, even reconstructing with a larger FOV does not guarantee a good estimate of metal location in the projections; and in the latter, the metal location in each projection is difficult to identify due to motion. Furthermore, two-pass methods increase the total reconstruction time. In this study, a projection-based metal detection and correction method with a dual layer detector is investigated. The dual layer detector provides dual energy images with perfect temporal and spatial registration in each projection, which aid in the identification of metal. A simple phantom with metal wires (copper) and a needle (steel) is used to evaluate the projection-based metal artifact reduction method from a dual layer scan and compared with that of a single layer scan. Preliminary results showed enhanced ability to identify metal regions, leading to substantially reduced metal artifact in reconstructed images. In summary, an effective single-pass, projection-domain method using a dual layer detector has been demonstrated, and it is expected to be robust against truncation and motion.

Intra-operative computed tomography in endovascular aneurysm repair

The study objective was to evaluate the ability of computed tomography (CT) to identify technical complications intra-operatively during endovascular aneurysm repair (EVAR). Frequency of complications seen by CT and their sequelae was compared with conventional completion angiography.

METHODS

We performed a systematic review that conformed to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines. We considered studies reporting on the effectiveness of intra-operative CT during EVAR.

RESULTS

Our literature search yielded six studies that met our criteria for inclusion. In general, these showed intra-operative CT to be superior to completion angiogram at detecting intra-operative complications during EVAR. Despite concerns regarding irradiation, the use of intra-operative CT was found to expose patients to an overall lower radiation dose, since post-operative CT angiograms were no longer required. Moreover, no adverse effect on renal function has been demonstrated as a result of the increased intra-operative contrast usage when CT is used.

CONCLUSIONS

The current body of evidence suggests that intra-operative CT is superior to completion angiography at detecting clinically important EVAR complications and incurs a lower total radiation dose with no added risk of contrast-induced renal impairment. Further research directly comparing the two modalities in the same cohort is required to determine sensitivity for individual complications.

Dedicated cone-beam breast CT using laterally-shifted detector geometry: Quantitative analysis of feasibility for clinical translation

BACKGROUND

High-resolution, low-noise detectors with minimal dead-space at chest-wall could improve posterior coverage and microcalcification visibility in the dedicated cone-beam breast CT (CBBCT). However, the smaller field-of-view necessitates laterally-shifted detector geometry to enable optimizing the air-gap for x-ray scatter rejection.

OBJECTIVE

To evaluate laterally-shifted detector geometry for CBBCT with clinical projection datasets that provide for anatomical structures and lesions.

METHODS

CBBCT projection datasets (n = 17 breasts) acquired with a 40×30 cm detector (1024×768-pixels, 0.388-mm pixels) were truncated along the fan-angle to emulate 20.3×30 cm, 22.2×30 cm and 24.1×30 cm detector formats and correspond to 20, 120, 220 pixels overlap in conjugate views, respectively. Feldkamp-Davis-Kress (FDK) algorithm with 3 different weighting schemes were used for reconstruction. Visual analysis for artifacts and quantitative analysis of root-mean-squared-error (RMSE), absolute difference between truncated and 40×30 cm reconstructions (Diff), and its power spectrum (PSDiff) were performed.

RESULTS

Artifacts were observed for 20.3×30 cm, but not for other formats. The 24.1×30 cm provided the best quantitative results with RMSE and Diff (both in units of μ, cm-1) of 4.39×10-3±1.98×10-3 and 4.95×10-4±1.34×10-4, respectively. The PSDiff (>0.3 cycles/mm) was in the order of 10-14μ2mm3 and was spatial-frequency independent.

CONCLUSIONS

Laterally-shifted detector CBBCT with at least 220 pixels overlap in conjugate views (24.1×30 cm detector format) provides quantitatively accurate and artifact-free image reconstruction.

Quantitative Evaluation of Bone Microstructure using High-Resolution Extremity Cone-Beam CT with a CMOS Detector

Purpose

A high-resolution cone-beam CT (CBCT) system for extremity imaging has been developed using a custom complementary metal-oxide-semiconductor (CMOS) x-ray detector. The system has spatial resolution capability beyond that of recently introduced clinical orthopedic CBCT. We evaluate performance of this new scanner in quantifying trabecular microstructure in subchondral bone of the knee.

Methods

The high-resolution scanner uses the same mechanical platform as the commercially available Carestream OnSight 3D extremity CBCT, but replaces the conventional amorphous silicon flat-panel detector (a-Si:H FPD with 0.137 mm pixels and a ~0.7 mm thick scintillator) with a Dalsa Xineos3030 CMOS detector (0.1 mm pixels and a custom 0.4 mm scintillator). The CMOS system demonstrates ~40% improved spatial resolution (FWHM of a ~0.1 mm tungsten wire) and ~4× faster scan time than FPD-based extremity CBCT (FPD-CBCT). To investigate potential benefits of this enhanced spatial resolution in quantitative assessment of bone microstructure, 26 trabecular core samples were obtained from four cadaveric tibias and imaged using FPD-CBCT (75 μm voxels), CMOS-CBCT (75 μm voxels), and reference micro-CT (μCT, 15 μm voxels). CBCT bone segmentations were obtained using local Bernsen's thresholding combined with global histogram-based pre-thresholding; μCT segmentation involved Otsu's method. Measurements of trabecular thickness (Tb.Th), spacing (Tb.Sp), number (Tb.N) and bone volume (BV/TV) were performed in registered regions of interest in the segmented CBCT and μCT reconstructions.

Results

CMOS-CBCT achieved noticeably improved delineation of trabecular detail compared to FPD-CBCT. Correlations with reference μCT for metrics of bone microstructure were better for CMOS-CBCT than FPD-CBCT, in particular for Tb.Th (increase in Pearson correlation from 0.84 with FPD-CBCT to 0.96 with CMOS-CBCT) and Tb.Sp (increase from 0.80 to 0.85). This improved quantitative performance of CMOS-CBCT is accompanied by a reduction in scan time, from ~60 sec for a clinical high resolution protocol on FPD-CBCT to ~17 sec for CMOS-CBCT.

Conclusion

The CMOS-based extremity CBCT prototype achieves improved performance in quantification of bone microstructure, while retaining other diagnostic capabilities of its FPD-based precursor, including weight-bearing imaging. The new system offers a promising platform for quantitative imaging of skeletal health in osteoporosis and osteoarthritis.

Cone-Beam Computed Tomography in Orthodontics

Unlike patients receiving implants or endodontic treatment, most orthodontic patients are children who are particularly sensitive to ionizing radiation. Cone-beam computed tomography (CBCT) carries risks and benefits in orthodontics. The principal risks and limitations include ionizing radiation, the presence of artifacts, higher cost, limited accessibility, and the need for additional training. However, this imaging modality has several recognized indications in orthodontics, such as the assessment of impacted and ectopic teeth, assessment of pharyngeal airway, assessment of mini-implant sites, evaluation of craniofacial abnormalities, evaluation of sinus anatomy or pathology, evaluation of root resorption, evaluation of the cortical bone plate, and orthognathic surgery planning and evaluation. CBCT is particularly justified when it brings a benefit to the patient or changes the outcome of the treatment when compared with conventional imaging techniques. Therefore, CBCT should be considered for clinical orthodontics for selected patients. Prescription of CBCT requires judicious and sound clinical judgment. The central question of this narrative review article is: when does CBCT add value to the practice of orthodontics? To answer this question, this article presents discussion on radiation dosage of CBCT and other imaging techniques used in orthodontics, limitations of CBCT in orthodontics, justifying the use of CBCT in orthodontics, and the benefits and evidence-based indications of CBCT in orthodontics. This review summarizes the central themes and topics in the literature regarding CBCT in orthodontics and presents ten orthodontic cases in which CBCT proved to be valuable.

Age and sex estimation based on pulp cavity volume using cone beam computed tomography: development and validation of formulas in a Brazilian sample

OBJECTIVES

To develop and validate formulas for age and sex estimation based on the pulp cavity volume of teeth using cone beam CT.

METHODS

The sample was composed of 116 cone beam CT scans from Brazilian individuals of both sexes, ranging in age from 13 to 70 years. A total of 232 teeth (upper central incisors and canines) were evaluated. Two calibrated examiners determined pulp cavity volumes using the ITK-SNAP software. Pearson's correlation test was used to assess the correlation between chronological age and pulp volume. Linear and logistic regression models were developed for age and sex estimation, respectively, and were validated in another sample of 72 teeth.

RESULTS

Pearson's correlation coefficients between age and pulp volume were negative and significant (p < 0.0001) for both teeth (r = -0.8782 for central incisors and r = -0.8738 for canines). The age estimation formulas showed good determination coefficients (adjusted R² = 0.7614 to 0.8367). For sex estimation, when the age was known, the coefficients were also good (adjusted R² = 0.649 to 0.812). However, when the age was unknown, the coefficients of the sex estimation formulas were low (adjusted R² = 0.047 to 0.393). Validation showed high accuracy of age estimation in individuals older than 35 years, as well as high accuracy of sex estimation when the age was known.

CONCLUSIONS

Our formulas provided excellent results and can be applied to the Brazilian population. The best results were observed for age estimation in females and for sex estimation when the age was known.

3D-cinematic rendering for dental and maxillofacial imaging

OBJECTIVES

Aim of this technical note is to show the applicability of cinematic rendering (CR) for a photorealistic 3-dimensional (3D) visualization of maxillofacial structures. The focus is on maxillofacial hard tissue pathologies.

METHODS

High density maxillofacial pathologies were selected in which CR is applicable. Data from both, CT and cone beam CT (CBCT) were postprocessed using a prototype CR software.

RESULTS

CR 3D postprocessing of CT and CBCT imaging data is applicable on high density structures and pathologies such as bones, teeth, and tissue calcifications. Image reconstruction allows for a detailed visualization of surface structures, their plasticity, and 3D configuration.

CONCLUSIONS

CR allows for the generation of photorealistic 3D reconstructions of high density structures and pathologies. Potential applications for maxillofacial bone and tooth imaging are given and examples for CT and CBCT images are displayed.

Incorporating Cone-Beam CT Into the Diagnostic Algorithm for Suspected Radiocarpal Fractures: A New Standard of Care?

OBJECTIVE. The purpose of this study was to assess the result of adding cone-beam CT to the standard imaging algorithm for patients with suspected radiographically occult traumatic radiocarpal fractures. SUBJECTS AND METHODS. A prospective review was performed on all patients who had cone-beam CT investigation of acute wrist pain after normal initial radiographs. Patients with no identified fractures were clinically reassessed and referred for MRI if concern for a fracture persisted. RESULTS. In all, 117 patients were assessed; 50.4% had fractures identified with a total of 67 radiographically occult fractures. One fracture was identified on MRI that was not seen on cone-beam CT. Cone-beam CT had sensitivity of 98.3% (95% CI, 91.1-100%), specificity of 100% (95% CI, 93.7-100%), positive predictive value of 100%, and negative predictive value of 98.3% (95% CI, 89.1-100%). Accuracy was 99.1% (95% CI, 95.3-100%). CONCLUSION. Incorporating cone-beam CT into routine clinical practice as part of a standardized diagnostic algorithm yielded a 50% fracture detection rate in patients with negative wrist radiographs but ongoing clinical concern for radiocarpal fracture. Cone-beam CT provides more diagnostic information than radiographs at a lower radiation dose than conventional MDCT. Given the poor accuracy of radiographs for acute radiocarpal fractures and the high fracture prevalence in this cohort, we feel that cone-beam CT should be regarded as the new standard of care in the investigation of these patients.

The image-guided operating room-Utility and impact on surgeon's performance in the head and neck surgery

BACKGROUND

The image-guided operating room (OR) is an emerging standard for dealing with complex cases in many surgical disciplines including neurosurgery, thoracic surgery, maxillofacial trauma, and orthopedic surgery. Its use in head and neck oncological surgery is not well established. The primary aim of this study was to assess the image quality of cone-beam CT (CBCT) under real clinical conditions. The secondary aim was to assess the effect on surgical performance and decision making.

METHODS

Intraoperative 3D imaging was performed using a CBCT capable C-Arm mounted on a multi-axis robot (Siemens Zeego) in the image-guided OR. All patients had immediate preoperative imaging taken with further intraoperative imaging performed as required. Ten initial patients, comprising 28 intraoperative scans, were used for questionnaire-based image reviews conducted with experienced head and neck clinicians. Scans were assessed for aspects of both image quality and clinical utility, on separate 5-point Likert scales (1-5).

RESULTS

The median rating for bony detail was 4 out of 5. Vascular detail was increased (P < 10^-8 ) from 1 to 3 with the use of IV contrast (region of interest CT# was 284 HU [SD, 47 HU]). Images were rated as 4 for freedom from artifact. Soft tissue definition was 2, with no significant improvement (P = .2) with the addition of IV iodinated contrast. Surgeons rated the greatest clinical utility (4) for the CBCT when assessing postreconstruction imaging of a complex case.

CONCLUSIONS

The image quality of CBCT in the image-guided OR is good for bony detail and complex oncological reconstructions in the head and neck setting but probably has limited benefit for intraoperative soft tissue delineation. Future studies must also focus on clinical outcomes to help demonstrate the value of the image-guided OR.

Known-component 3D image reconstruction for improved intraoperative imaging in spine surgery: A clinical pilot study

PURPOSE

Intraoperative imaging plays an increased role in support of surgical guidance and quality assurance for interventional approaches. However, image quality sufficient to detect complications and provide quantitative assessment of the surgical product is often confounded by image noise and artifacts. In this work, we translated a three-dimensional model-based image reconstruction (referred to as "Known-Component Reconstruction," KC-Recon) for the first time to clinical studies with the aim of resolving both limitations.

METHODS

KC-Recon builds upon a penalized weighted least-squares (PWLS) method by incorporating models of surgical instrumentation ("known components") within a joint image registration-reconstruction process to improve image quality. Under IRB approval, a clinical pilot study was conducted with 17 spine surgery patients imaged under informed consent using the O-arm cone-beam CT system (Medtronic, Littleton MA) before and after spinal instrumentation. Volumetric images were generated for each patient using KC-Recon in comparison to conventional filtered backprojection (FBP). Imaging performance prior to instrumentation ("preinstrumentation") was evaluated in terms of soft-tissue contrast-to-noise ratio (CNR) and spatial resolution. The quality of images obtained after the instrumentation ("postinstrumentation") was assessed by quantifying the magnitude of metal artifacts (blooming and streaks) arising from pedicle screws. The potential low-dose advantages of the algorithm were tested by simulating low-dose data (down to one-tenth of the dose of standard protocols) from images acquired at normal dose.

RESULTS

Preinstrumentation images (at normal clinical dose and matched resolution) exhibited an average 24.0% increase in soft-tissue CNR with KC-Recon compared to FBP (N = 16, P = 0.02), improving visualization of paraspinal muscles, major vessels, and other soft-tissues about the spine and abdomen. For a total of 72 screws in postinstrumentation images, KC-Recon yielded a significant reduction in metal artifacts: 66.3% reduction in overestimation of screw shaft width due to blooming (P < 0.0001) and reduction in streaks at the screw tip (65.8% increase in attenuation accuracy, P < 0.0001), enabling clearer depiction of the screw within the pedicle and vertebral body for an assessment of breach. Depending on the imaging task, dose reduction up to an order of magnitude appeared feasible while maintaining soft-tissue visibility and metal artifact reduction.

CONCLUSIONS

KC-Recon offers a promising means to improve visualization in the presence of surgical instrumentation and reduce patient dose in image-guided procedures. The improved soft-tissue visibility could facilitate the use of cone-beam CT to soft-tissue surgeries, and the ability to precisely quantify and visualize instrument placement could provide a valuable check against complications in the operating room (cf., postoperative CT).

Relationship between the Position of Impacted Third Molars and External Root Resorption of Adjacent Second Molars: A Retrospective CBCT Study

BACKGROUND AND OBJECTIVES

Impacted third molars (ITM) are the most commonly-impacted teeth. There is a risk for ITM to cause a number of pathological conditions, and external root resorption (ERR) of adjacent teeth is one of the most prevalent. Retaining or prophylactic extraction of ITM is a polemic topic. External root resorption of adjacent teeth is one of possible indications for prophylactic removal of ITM. The aim of this study was to assess the relationship between external root resorption (ERR) on the distal aspect of second molars' roots and positional parameters of ITM. Methods: Cone beam computed tomography scans of 109 patients (41 males, 68 females; mean age 26.4 ± 7.9 years) with 254 ITM (131 in the maxilla and 123 in the mandible) were retrospectively analyzed. Positional parameters of ITM (mesio-distal position, angulation, impaction depth, and available eruption space) were evaluated. The presence, location, and depth of ERR of adjacent second molars were assessed. Results: Analysis showed a relationship between ITM impaction depth, mesial inclination angle, and the presence of ERR. Mesial inclination angle of more than 13.6° increased the odds of ERR occurrence by 5.439 (95% CI, 2.97-9.98). ITM presence at the level of ½ of roots of the adjacent second molar or more apically increased the odds of ERR occurrence by 2.218 (95% CI, 1.215-4.048). No significant correlation was detected between the occurrence of ERR and patient age, gender, or the available eruption space in the mandible. Depth of ERR did not depend on its location. Conclusions: Incidence of ERR in second molars is significantly associated with mesial inclination and a deep position of ITM.

[Multimodal imaging during lung and abdominal stereotactic ablative radiotherapy: from cine MRI through 3D/4D CBCT to intrafractional kV verification]

Our aim was to present our treatment and verification protocols of linear accelerator-based lung and abdominal stereotactic ablative radiotherapy (SABR). During our treatments both the volumetric imaging (3D/4D CBCT/CT) and triggered kV intrafractional tumor motion control could be combined allowing a full control on the whole workflow. The most optimal kV directions from which the tumor is well detectable were defined. Tumor movements measured on cine MRI in treatment position correlated well with the ones on 4D CBCT, thus cine MRI is considered an excellent device to pre-select the appropriate image/treatment verification SABR protocol. In abdominal targets implanted markers and cine MRI are preferred due to limited image quality of CBCT with the current version. In selected lung SABR cases (≥8mm motion) the dose delivery of organs at risk (lungs - GTV, chest wall) could be reduced compared to free breathing conditions, however, the treatment time is at least two-folds higher.

Known-Component Model-Based Material Decomposition for Dual Energy Imaging of Bone Compositions in the Presence of Metal Implant

Dual energy computed tomography (DE CT) is a promising technology for the assessment of bone compositions. One of potential applications involves evaluations of fracture healing using longitudinal measurements of callus mineralization. However, imaging of fractures is often challenged by the presence of metal fixation hardware. In this work, we report on a new simultaneous DE reconstruction-decomposition algorithm that integrates the previously introduced Model-Based Material Decomposition (MBMD) with a Known-Component (KC) framework to mitigate metal artifacts. The algorithm was applied to the DE data obtained on a dedicated extremity cone-beam CT (CBCT) with capability for weight-bearing imaging. To acquire DE projections in a single gantry rotation, we exploited a unique multisource design of the system, where three X-ray sources were mounted parallel to the axis of rotation. The central source provided high energy (HE) data at 120 kVp, while the two remaining sources were operated at a low energy (LE) of 60 kVp. This novel acquisition trajectory further motivates the use of MBMD to accommodate this complex DE sampling pattern. The algorithm was validated in a simulation study using a digital extremity phantom. The phantom consisted of a water background with an insert containing varying concentrations of calcium (50 - 175 mg/mL). Two configurations of titanium implants were considered: a fixation plate and an intramedullary nail. The accuracy of calcium-water decompositions obtained with the proposed KC-MBMD algorithm was compared to MBMD without metal component model. Metal artifacts were almost completely removed by KC-MBMD. Relative absolute errors of calcium concentration in the vicinity of metal were 6% - 31% for KC-MBMD (depending on the calcium insert and implant configuration), compared favorably to 48% - 273% for MBMD. Moreover, accuracy of concentration estimates for KC-MBMD in the presence of metal implant approached that of MBMD in a configuration without implant (6%-23%). The proposed algorithm achieved accurate DE material decomposition in the presence of metal implants using a non-conventional, axial multisource DE acquisition pattern.

The detection of vertical root fractures in post-core restored teeth with cone-beam CT: in vivo and ex vivo

OBJECTIVES

To compare the accuracy of cone-beam CT ex vivo and in vivo for the detection of artificially created large and small vertical root fractures in extracted teeth restored with post-core.

METHODS

Individual metal cast post-cores were fixed in the root canals of 50 extracted single-rooted human teeth. In 30 teeth fractures were created by tapping posts with a hammer. The teeth were sterilised in autoclave and embedded into bite-plates made of silicon impression material. Cone-beam CT scanning was performed ex vivo and in vivo . For the in vivo scanning, teeth in sterile plastic bags were inserted into the mouths of volunteers. Then the teeth were sectioned with low-speed saw and the widths of the VRFs were measured microscopically. The teeth were distributed into 2 groups in accordance with the measured fractures' widths: large (wider than 180-250 µm) and small (80-150 µm). Five observers assessed the presence of vertical root fractures on axial CBCT slices. Sensitivity, specificity, accuracy and inter examiner agreement were calculated.

RESULTS

The accuracy of cone-beam CT in vitro for large and small vertical root fractures detection was 0.56 and 0.40 respectively (p = 0.043). The sensitivity values were 0.53 and 0.27 for large and small vertical root fractures, respectively (p = 0.043). The visualisation of fracture lines in vivo was impossible in 90 % of cases, because of low image quality. Inter examiner reliability analysis showed κ values ranging from 0.02 to 0.54.

CONCLUSIONS

Fracture width affected the in vitro detectability of vertical root fractures by cone-beam CT in teeth with metal cast post-cores. The detectability of root fractures in vivo was decreased because of low image quality, making the assessment of sound tooth tissue impossible.

Alveolar ridge preservation in the posterior maxilla reduces vertical dimensional change: A randomized controlled clinical trial

OBJECTIVES

To test whether or not alveolar ridge preservation reduces vertical changes in the posterior maxilla compared to spontaneous healing following tooth extraction.

MATERIALS AND METHODS

Forty subjects requiring extraction of maxillary posterior teeth with root apices protruding into the maxillary sinus floor were consecutively enrolled. Patients were randomly assigned to either one of two surgical interventions: an alveolar ridge preservation procedure using collagenated bovine bone mineral and a resorbable collagen membrane (test) or no grafting (control). Cone-beam computed tomographies were taken immediately and at 6 months after surgery, prior to dental implant placement.

RESULTS

Based on radiographic data, the level of the sinus floor remained stable over time (baseline to 6 months) in the test group (-0.14 mm [-0.31, -0.02]). In the control group, the sinus floor level shifted more coronally (-1.16 mm [-1.73, -0.61]) than the test group (p < 0.05). The test group demonstrated a significantly larger residual bone height than the control group at 6 months (7.30 mm [6.36, 8.20] vs. 4.83 mm [3.94, 5.76], respectively, p < 0.05). Implant placement without any additional sinus augmentation procedure was performed in 42.9% of test group cases, whereas in all of the subjects in the control group an additional augmentation procedure was needed (100% of the cases).

CONCLUSION

Alveolar ridge preservation in the posterior maxilla maintained the vertical bone height more efficiently and resulted in less need for sinus augmentation procedures at 6 months compared to spontaneous healing.

Correlation between prevelance of Haller cells and postoperative maxillary sinusitis after sinus lifting Procedure

Our aim was to investigate the prevalence of Haller cells in a group of patients listed for sinus lifting, and to assess the correlation between postoperative maxillary sinusitis and their presence. A total of 102 patients (150 sides) were evaluated retrospectively on cone-beam computed tomography (CT). The presence and dimensions of Haller cells were noted on the scans. The development of postoperative maxillary sinusitis was recorded. Fisher's exact test was used for statistical evaluation and probabilities of less than 0.05 were considered significant. Maxillary sinusitis developed after sinus lifting in five patients, and Haller cells were found in three of them. However, there was no correlation between the presence of Haller cells and postoperative maxillary sinusitis (p=0.638). The cells were larger in patients with postoperative maxillary sinusitis, and the greater dimensions may be a potential risk factor for developing it after a sinus lift.

Evaluation of a mobile C-arm cone-beam CT in interstitial high-dose-rate prostate brachytherapy treatment planning

Introduction

The aim of this study was to evaluate the suitability of using cone‐beam computed tomography (CBCT) obtained with a mobile C‐arm X‐ray fluoroscopy unit as a single modality for planning of high‐dose‐rate (HDR) prostate brachytherapy treatments.

Methods

The feasibility of using CBCT images obtained using a Siemens Arcadis Orbic 3D mobile C‐arm was evaluated. A retrospective clinical study was undertaken of six participants undergoing HDR prostate brachytherapy. Plans generated using images from a Toshiba Aquilion One LB CT were compared with those generated using CBCT images. After rigid spatial registration, the plans were compared based on various parameters such as dose‐volume histograms, overlap quantities and metrics, and dose constraints.

Results

Provided they were within the limited field of view, the brachytherapy catheters and fiducial markers were clearly visible in the CBCT images and thus, localisable and identifiable in the treatment planning process. The Siemens CBCT underestimated CT numbers leading to poorer tissue contrast which exacerbated the difficulties in delineation of the target tumour and the surrounding organs at risk. Between CT‐ and CBCT‐based plans, the mean difference of CTV‐D₉₀ was 1.58 Gy, CTV‐V₁₀₀ was 12.13%, rectum‐V₈₀ was 0.06% and urethra‐V₁₂₀ was −0.70%.

Conclusion

It was not feasible to solely utilise the Siemens Arcadis Orbic 3D for HDR prostate brachytherapy treatment planning due to suboptimal organ delineation. However, the methods in this study could be used to evaluate other mobile CBCT imaging devices for feasibility in HDR brachytherapy treatment planning since the results indicated that it may not be necessary to have standard quality CT images for treatment planning.

Automatic diaphragm segmentation for real-time lung tumor tracking on cone-beam CT projections: a convolutional neural network approach

PURPOSE

To automatically segment the diaphragm on individual lung cone-beam CT projection images, to enable real-time tracking of lung tumors using kilovoltage imaging.

METHODS

The deep neural network Mask R-CNN was trained on 3500 raw cone-beam CT projection images from 10 lung cancer patients, with the diaphragm manually segmented on each image used as a ground truth label. Ground-truth breathing traces were extracted from each patient for both diaphragm hemispheres, and apex positions were compared against the predicted output of the neural network. Ten-fold cross-validation was used to evaluate the segmentation accuracy.

RESULTS

The mean diaphragm apex prediction error was 4.4 mm. The mean percentage of projection images for which a successful prediction could me made was 87.3%. Prediction accuracy at some lateral gantry angles was worse due to overlap between diaphragm hemispheres, and the increased amount of fatty tissue.

CONCLUSIONS

The neural network was able to track the diaphragm apex position successfully. This allows accurate assessment of the breathing phase, which can be used to estimate the position of the lung tumor in real time.