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Objective. The TOol for PArticle Simulation (TOPAS) is a Geant4-based Monte Carlo software application that has been used for both research and clinical studies in medical physics. So far, most users of TOPAS have focused on radiotherapy-related studies, such as modeling radiation therapy delivery systems or patient dose calculation. Here, we present the first set of TOPAS extensions to make it easier for TOPAS users to model medical imaging systems.Approach. We used the extension system of TOPAS to implement pre-built, user-configurable geometry components such as detectors (e.g. flat-panel and multi-planar detectors) for various imaging modalities and pre-built, user-configurable scorers for medical imaging systems (e.g. digitizer chain).Main results. We developed a flexible set of extensions that can be adapted to solve research questions for a variety of imaging modalities. We then utilized these extensions to model specific examples of cone-beam CT (CBCT), positron emission tomography (PET), and prompt gamma (PG) systems. The first of these new geometry components, the FlatImager, was used to model example CBCT and PG systems. Detected signals were accumulated in each detector pixel to obtain the intensity of x-rays penetrating objects or prompt gammas from proton-nuclear interaction. The second of these new geometry components, the RingImager, was used to model an example PET system. Positron-electron annihilation signals were recorded in crystals of the RingImager and coincidences were detected. The simulated data were processed using corresponding post-processing algorithms for each modality and obtained results in good agreement with the expected true signals or experimental measurement.Significance. The newly developed extension is a first step to making it easier for TOPAS users to build and simulate medical imaging systems. Together with existing TOPAS tools, this extension can help integrate medical imaging systems with radiotherapy simulations for image-guided radiotherapy.

Purpose: Analysis of cochlear structures and postoperative temporal bone (TB) imaging are gaining importance in the evaluation of cochlear implantation (CI°). Our aims were to explore the microarchitecture of human cochlea using micro-computed tomography (μCT), analyze electrode's placement inside cochlea after CI°, and compare pre-/post-implantation μCT scans with cone-beam CT (CBCT) scans of same TBs. Methods: Cadaveric TBs were scanned using μCT and CBCT then underwent CI° using straight electrodes. Thereafter, they underwent again μCT and CBCT-imaging. Results: Ten TBs were studied. μCT allowed visualization of scala tympani, scala vestibuli, basilar membrane, osseous spiral lamina, crista fenestrae, and spiral ligament. CBCT showed same structures except spiral ligament and crista fenestrae. After CI°, μCT and CBCT displayed the scalar location and course of electrode array within the cochlea. There were 7 cases of atraumatic electrode insertion and 3 cases of insertion trauma: basilar membrane elevation, electrode foldover with limited migration into scala vestibuli, and electrode kinking with limited migration into scala vestibuli. Insertion trauma was not correlated with cochlea's size or crista's maximal height but with round window membrane diameter. Resolution of μCT was higher than CBCT but electrode artifacts were similar. Conclusions: μCT was accurate in visualizing cochlear structures, and course and scalar position of electrode array inside cochlea with any possible trauma to cochlea or array. CBCT offers a good alternative to μCT in clinical practice for cochlear imaging and evaluation of CI°, with lower radiation and higher resolution than multi-slice CT. Difficulties related to non-traumatic CI° are multifactorial. [ABSTRACT FROM AUTHOR]

Background: Various mechanisms suggest that periodontal pathogens and inflammatory processes contribute to systemic pathogenic processes such as atherosclerosis. This study investigated the possibility of a correlation between the presence of incidentally found calcifications along the course of the internal carotid artery (ICA) and tooth loss and periodontal status.Methods: A retrospective CBCT analysis was performed on 110 patients. CBCT scans obtained as a part of the dental examinations were analyzed for missing teeth and evidence of any calcification along the ICA course. The mean age, gender, and the total number of missing teeth for all scans revealing calcifications were evaluated. Results: The study sample consisted of 110 scans, with the cohort’s mean age (SD) of 50.01 (±11.6) and gender distribution of 53.4% females and 43.6% males. A total of 17% of the scans exhibited the presence of calcification. A comparison of missing teeth between the two groups revealed that the group with calcification exhibited more missing teeth, which was statistically significant with a p-value of 0.01. Comparison of the apical lesions between the two groups revealed that apical lesion was higher in the group with calcification and was statistically significant with a p-value of 0.011.Conclusions: The greater the number of missing teeth, the higher the chances of calcifications being detected along the course of the ICA.

BACKGROUND: Various mechanisms suggest that periodontal pathogens and inflammatory processes contribute to systemic pathogenic processes such as atherosclerosis. This study investigated the possibility of a correlation between the presence of incidentally found calcifications along the course of the internal carotid artery (ICA) and tooth loss and periodontal status. METHODS: A retrospective CBCT analysis was performed on 110 patients. CBCT scans obtained as a part of the dental examinations were analyzed for missing teeth and evidence of any calcification along the ICA course. The mean age, gender, and the total number of missing teeth for all scans revealing calcifications were evaluated. RESULTS: The study sample consisted of 110 scans, with the cohort’s mean age (SD) of 50.01 (±11.6) and gender distribution of 53.4% females and 43.6% males. A total of 17% of the scans exhibited the presence of calcification. A comparison of missing teeth between the two groups revealed that the group with calcification exhibited more missing teeth, which was statistically significant with a p-value of 0.01. Comparison of the apical lesions between the two groups revealed that apical lesion was higher in the group with calcification and was statistically significant with a p-value of 0.011. CONCLUSIONS: The greater the number of missing teeth, the higher the chances of calcifications being detected along the course of the ICA. [ABSTRACT FROM AUTHOR]

Accurate knowledge of the acquisition geometry of a CT scanning system is key for high quality tomographic imaging. Unfortunately, in modular X-ray CT setups, geometry misalignment occurs each time the setup is changed, which calls for an efficient calibration procedure to correct for geometric inaccuracies. Although many studies have been dealing with the calibration of X-ray CT systems, these are often specifically designed for one setup and/or expensive. In this work, we explore the possibilities of a low-cost, easy-to-build, and modular phantom, constructed from LEGO bricks, which serves as a structure to hold small metal beads, for geometric calibration of a tomographic X-ray system. By estimating the bead coordinates using deep learning, and minimizing center-to-center distances of the metal beads between measured and reference projection data, geometry parameters are derived. With simulated as well as real experiments, it is shown that the LEGO phantom can be used to accurately estimate the geometry of a modular X-ray CT system. [ABSTRACT FROM AUTHOR]

Accurate assessment of the location of the maxillary sinuses, incisive canal, and nasal cavity, as well as the height, width, and angulation of bone is essential for implant treatment planning. The purpose of this study was to introduce the clinical application of a cone-beam computerized tomography system (Ortho- CT} to assess multiple two-dimensional (2D) images for the preoperative treatment planning of maxillary implants To evaluate The multiple 2D images scanned using the Ortho-GT system the maxillary region placed with radiopaque template in the maxilla. Ortho-CT images provided useful information for evaluai- ing the morphology of the maxilla, for locating the incisive canal, maxillary sinuses, nasal cavity, and for showing the relationship of The template to the bone. It is concluded That the Ortho-CT system is a useful aid for diagnosis and treatment planning (or maxillary implant treatment. (QuWessence M 2004,35: 525-528) [ABSTRACT FROM AUTHOR]

Certain cavernous sinus (CS) dural arteriovenous fistulas (DAVFs) are difficult to access through transarterial or transvenous routes and may necessitate access through direct transorbital puncture of the superior ophthalmic vein (SOV) or the CS. However, to be successful, the accurate design of the puncture route and guidance are crucial. This study aimed to report our preliminary clinical experience using cone-beam computed tomography (CT) with real-time fluoroscopic overlays for image guidance during transorbital needle puncture. Between December 2017 and July 2018, 3 patients with CS DAVFs were treated via a transorbital puncture to establish access to the CS under the guidance of XperGuide planning software either via direct CS puncture or through the SOV. The guidance trajectory was superimposed onto the real-time fluoroscopic image during needle puncture. Once access was established, the CS DAVFs were treated with a combination of liquid embolic materials and coils. Image guidance aided to avoid at-risk structures and treatment resulted in all cases in complete obliteration of the CS DAVFs as verified by control angiography without peri- or postprocedural complications. Endovascular embolization of CS DAVFs via direct transorbital puncture aided by image guidance provided an alternative option when more conventional approaches are deemed not possible. [ABSTRACT FROM AUTHOR]

Atlantoaxial rotatory subluxation (AARS) is a rare pathological condition of the upper cervical spine. It can be caused by multiple mechanisms, including minor neck manipulations. Children are more prone owing to the weaker periarticular soft tissue and a steeper slant of the C1 facet plane against the vertical axis of the dens. If AARS does not resolve spontaneously, a normal position of the atlantoaxial joint must be achieved by reduction and stabilization. A 15-year-old girl had presented with a painful torticollis that had already been present for 4 weeks after trimaxillary jaw correction for skeletal class II malocclusion. A computed tomography (CT) scan of the cervical spine showed AARS Field and Hawkins classification type I. We first attempted 1 week of conservative treatment with a soft collar and the prescription of a muscular relaxant. However, because the AARS persisted, we performed transoral closed reduction with the patient under general anesthesia, as previously described. During the procedure, we used intraoperative cone-beam CT to evaluate the degree of reduction. After obtaining complete reduction, immobilization with a halo-vest was applied. Complete reduction of the AARS was achieved with closed intraoral reduction. We used intraoperative cone-beam CT to confirm complete reduction. We found cone-beam CT to be a very useful tool. [ABSTRACT FROM AUTHOR]

Structured Abstract Objectives To investigate variability in the upper airway of subjects with different anteroposterior skeletal patterns by evaluating the volume and the most constricted cross-sectional area of the pharyngeal airway and defining correlations between the different variables. Material and methods The study sample consisted of 60 patients (29 boys, 31 girls) divided into three groups: Class I (1 ≤ ANB≤3), Class II ( ANB>3), and Class III ( ANB<1), to evaluate how the jaw relationship affects the airway volume and the most constricted cross-sectional area (Min- CSA). Differences between groups were determined using the Tukey-Kramer test. Correlations between variables were tested using Pearson's correlation coefficient. Results The volume and the Min- CSA of the pharyngeal airway ( PA) were significantly related to anteroposterior skeletal patterns ( p < 0.05). The nasopharyngeal airway ( NA) volume of Class I and Class III subjects was significantly larger than that of Class II subjects ( p < 0.05). The Min- CSA and the length of PA were significantly related to the volume of PA ( p < 0.05). The site and the size of the Min- CSA varied among the three groups. Conclusions The volume and the most constricted cross-sectional area of the airway varied with different anteroposterior skeletal patterns. The NA volume of Class I and Class III subjects was significantly larger than that of patients with a Class II skeletal pattern. [ABSTRACT FROM AUTHOR]

Cone-beam (CB) computed tomography (CT) is widely used in the field of medical imaging for guidance. Inspired by Betram's directional interpolation (BDI) methods, directional sinogram interpolation (DSI) was implemented to generate more CB projections by optimized (iterative) double-orientation estimation in sinogram space and directional interpolation. A new CBCT was subsequently reconstructed with the Feldkamp algorithm using both the original and interpolated CB projections. The proposed method was evaluated on both phantom and clinical data, and image quality was assessed by correlation ratio (CR) between the interpolated image and a gold standard obtained from full measured projections. Additionally, streak artifact reduction and image blur were assessed. In a CBCT reconstructed by 40 acquired projections over an arc of 360 degree, streak artifacts dropped 20.7% and 6.7% in a thorax phantom, when our method was compared to linear interpolation (LI) and BDI methods. Meanwhile, image blur was assessed by a head-and-neck phantom, where image blur of DSI was 20.1% and 24.3% less than LI and BDI. When our method was compared to LI and DI methods, CR increased by 4.4% and 3.1%. Streak artifacts of sparsely acquired CBCT were decreased by our method and image blur induced by interpolation was constrained to below other interpolation methods. [ABSTRACT FROM AUTHOR]

Objective: To determine the optimal intra-articular iodine concentration for C-arm flat-panel computed tomography (FPCT) arthrography using advanced joint phantoms and to evaluate its application in human cadaveric wrists and elbows. Multi-detector (MD) CT served as the standard of reference. Materials and methods: Joint phantoms and 10 human cadaveric wrist and elbow joints were scanned with C-arm FPCT (5-s, 8-s, and 20-s runs) and standard MDCT using different and optimal concentrations of iodinated contrast material. CT numbers of contrast material, tissue, and noise were measured and contrast-to-noise ratios (CNR) calculated for quantitative analysis. Image and depiction of cartilage, bone, and soft tissues were rated. Radiation doses were compared. Results: In FPCT, iodine concentrations positively correlated with CT numbers and noise of contrast material and with radiation dose ( r = 0.713-0.996, p < 0.05 each). At an iodine concentration of 45 mg/ml, CNR of cartilage and soft tissues were highest for all FPCT acquisitions and higher than in MDCT. The 20-s FPCT run performed best for image quality and depiction of anatomical structures and was rated overall equal to MDCT ( p = 0.857). Conclusion: The optimal iodine concentration for C-arm FPCT arthrography in this study is 45 mg/ml, leading to superior CNR and image quality for an optimal FPCT protocol compared with standard MDCT arthrography in human cadaveric joints. [ABSTRACT FROM AUTHOR]

Objective To evaluate the radiographic changes of the alveolar ridge following application of different ridge preservation techniques 6 months after tooth extraction. Materials and Methods Four treatment modalities were randomly assigned in 40 patients: β-tricalcium-phosphate-particles with polylactid coating (β- TCP), demineralized bovine bone mineral with 10% collagen covered with a collagen matrix ( DBBM-C/ CM), DBBM-C covered with an autogenous soft-tissue graft ( DBBM-C/ PG) and spontaneous healing (control). Cone-beam computed tomography scans were performed after treatment and 6 months later. Results After 6 months, the vertical changes ranged between −0.6 mm (−10.2%) for control and a gain of 0.3 mm (5.6%) for DBBM-C/ PG on the lingual side, and between −2.0 mm (−20.9%) for β- TCP and a gain of 1.2 mm (8.1%) for DBBM-C/ PG on the buccal side. The most accentuated ridge width changes were recorded 1 mm below the crest: −3.3 mm (−43.3%, C), −6.1 mm (−77.5%, β- TCP), −1.2 mm (−17.4%, DBBM-C/ CM) and −1.4 mm (−18.1%, DBBM-C/ PG). At all three levels, DBBM-C with either CM or PG was not significantly differing ( p > 0.05), while most other differences between the groups reached statistical significance ( p < 0.05). Conclusions Application of DBBM-C, covered with CM or PG, resulted in less vertical and horizontal changes of the alveolar ridge as compared with controls 6 months after extraction. [ABSTRACT FROM AUTHOR]

The temporomandibular joint has many complex anatomical and functional features compared with other joints. Therefore, caution should be exercised in the diagnosis of temporomandibular joint fractures. Although panoramic tomography is widely used for the screening of orofacial trauma as well as other diseases, this modality often overlooks evidence of a condylar fracture. Cone-beam computed tomography is also used for diagnosing orofacial diseases. The purposes of this report are to show the usefulness of cone-beam computed tomography in diagnosing condylar fractures and to describe the imaging features of condylar fractures. [ABSTRACT FROM AUTHOR]

Objective Stable esthetic restoration is required for anterior dental implants, assessed over a long-term follow-up. Cross-sectional images obtained using cone-beam computed tomography ( CBCT) allow visualization of the bucco-lingual bone surrounding dental implants; however, the thin labial bone surrounding anterior dental implants is unclear. So, the minimum labial bone thickness surrounding dental implants detected using CBCT images was estimated in the present in vitro study. Materials and methods One dry mandible with five aluminum steps and a titanium rod for simulation of the thin labial bone and dental implant were used. CBCT was performed three times using three exposure volumes, and voxel values of each aluminum step were plotted. Then, the maximum voxel value in each aluminum step as a percentage of that of the 1-mm-thick aluminum step was calculated. Results The rates for the 0.6-mm-thick aluminum step with a 51- and 102-mm-diameter exposure volume were approximately 50% or greater. Conclusions When labial bone surrounding the dental implant was approximately 0.6 mm or greater, it was suggested that it might be visually detectable using CBCT images with a 51- and 102-mm-diameter exposure volume. [ABSTRACT FROM AUTHOR]

Head motion during Computer Tomographic (CT) studies can adversely affects the reconstructed image through distortion and other artifacts such as blurring and doubling, thereby contributing to misdiagnosis of diseases. In this paper, we propose a method to detect and mitigate motion artifacts in three-dimensional (3D) cone-beam CT system. Motion detection is achieved by comparing the correlation coefficient between the adjacent x-ray projections. Artifacts, caused by motion, are mitigated either by replacing motion corrupted projections with their counterpart 180° apart projections under certain conditions, or by estimating motion corrupted projections using Least Square Support Vector Machine (LS-SVM) based time series prediction. The method has been evaluated on 3D Shepp-Logan phantom. In this research, Feldkamp-David-Kress (FDK) based back-projection algorithm is used for 3D reconstruction process. Computer simulation validates the motion detection and artifacts elimination mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Background and purpose: Pancreatic radiotherapy (RT) is limited by uncertain target motion. We quantified 3D patient/organ motion during pancreatic RT and calculated required treatment margins. Materials and methods: Cone-beam computed tomography (CBCT) and orthogonal fluoroscopy images were acquired post-RT delivery from 13 patients with locally advanced pancreatic cancer. Bony setup errors were calculated from CBCT. Inter- and intra-fraction fiducial (clip/seed/stent) motion was determined from CBCT projections and orthogonal fluoroscopy. Results: Using an off-line CBCT correction protocol, systematic (random) setup errors were 2.4 (3.2), 2.0 (1.7) and 3.2 (3.6)mm laterally (left–right), vertically (anterior–posterior) and longitudinally (cranio-caudal), respectively. Fiducial motion varied substantially. Random inter-fractional changes in mean fiducial position were 2.0, 1.6 and 2.6mm; 95% of intra-fractional peak-to-peak fiducial motion was up to 6.7, 10.1 and 20.6mm, respectively. Calculated clinical to planning target volume (CTV–PTV) margins were 1.4cm laterally, 1.4cm vertically and 3.0cm longitudinally for 3D conformal RT, reduced to 0.9, 1.0 and 1.8cm, respectively, if using 4D planning and online setup correction. Conclusions: Commonly used CTV–PTV margins may inadequately account for target motion during pancreatic RT. Our results indicate better immobilisation, individualised allowance for respiratory motion, online setup error correction and 4D planning would improve targeting. [Copyright &y& Elsevier]

Objective: To identify the right and left difference of the facial soft tissue landmarks three-dimensionally from the subjects of normal occlusion individuals. Materials and Methods: Cone-beam computed tomography (CT) scans were obtained in 48 normal occlusion adults (24 men, 24 women), and reconstructed into 3-dimensional (3D) models by using a 3D image soft ware. 3D position of 27 soft tissue landmarks, 9 midline and 9 pairs of bilateral landmarks, were identifi ed in 3D coordination system, and their right and left differences were calculated and analyzed. Results: The right and left difference values derived from the study ranged from 0.6 to 4.6 mm indicating a high variability according to the landmarks. In general, the values showed a tendency to increase according to the lower and lateral positioning of the landmarks in the face. Overall diff erences were determined not only by transverse differences but also by sagittal and vertical differences, indicating that 3D evaluation would be essential in the facial soft tissue analysis. Conclusions: Means and standard deviations of the right and left diff erence of facial soft tissue landmarks derived from this study can be used as the diagnostic standard values for the evaluation of facial asymmetry. [ABSTRACT FROM AUTHOR]

Abstract: Purpose: Kilovoltage flat-panel imaging systems are used for cone-beam Computed Tomography (CBCT) and digital Tomosynthesis (DTS). Hereby, the presence of scatter and relatively large dose from imaging are challenging factors. In this study a phenomenological beam model was developed to characterize imager response to imaging beams with a bow-tie filter (Varian OBI system). Materials and method: The kilovoltage beam model was based on dose ratio formalism and thus was using standard concepts of megavoltage dose calculation such as scatter factors, tissue maximum ratio and off-axis ratio. Primary and scatter (head and phantom scatter) were modeled with three Gaussian kernels. Parameters were based on measured transmission images for slabs of solid water of different total thickness and various jaw settings. Results: The beam model was used to evaluate contributions from primary, secondary and tertiary contributions for different geometrical objects such as cylinders and step-like phantoms. Theoretical predictions of radiographs using the model for known objects are consistent with the measurements. Conclusion: Secondary and tertiary contributions were interpreted as scatter and can be subtracted from CBCT projections based on the analytical model. Therefore our model can provide a basis for improvement of image quality (less artifacts due to scatter, better contrast and resolution) in CBCT reconstruction. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to compare setup errors obtained with kilovoltage cone-beam computed tomography (CBCT) and 2 different kinds of reference images, free-breathing 3D localization CT images (FB-CT) and the average images of 4-D localization CT images (AVG-CT) for phantom and lung cancer patients. This study also explored the correlation between the difference of translational setup errors and the gross tumor volume (GTV) motion. A respiratory phantom and 14 patients were enrolled in this study. For phantom and each patient, 3D helical CT and 4D CT images were acquired, and AVG-CT images were generated from the 4D CT. The setup errors were determined based on the image registration between the CBCT and the 2 different reference images, respectively. The data for both translational and rotational setup errors were analyzed and compared. The GTV centroid movement as well as its correlation with the translational setup error differences was also evaluated. In the phantom study, the AVG-CT method was more accurate than the FB-CT method. For patients, the translational setup errors based on FB-CT were significantly larger than those from AVG-CT in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) directions (p < 0.05). Translational setup errors differed by >1 mm in 32.6% and >2 mm in 12.9% of CBCT scans. The rotational setup errors from FB-CT were significantly different from those from AVG-CT in the LR and AP directions (p < 0.05). The correlation coefficient of the translational setup error differences and the GTV centroid movement in the LR, SI, and AP directions was 0.515 (p = 0.060), 0.902 (p < 0.001), and 0.510 (p = 0.062), respectively. For lung cancer patients, respiration may affect the on-line target position location. AVG-CT provides different reference information than FB-CT. The difference in SI direction caused by the 2 methods increases with the GTV movement. Therefore, AVG-CT should be the prefered choice of reference images. [Copyright &y& Elsevier]

The utilization of 3D computerized systems has allowed more effective procedures for forensic facial reconstruction. Three 3D computerized facial reconstructions were produced using skull models from live adult Korean subjects to assess facial morphology prediction accuracy. The 3D skeletal and facial data were recorded from the subjects in an upright position using a cone-beam CT scanner. Shell-to-shell deviation maps were created using 3D surface comparison software, and the deviation errors between the reconstructed and target faces were measured. Results showed that 54%, 65%, and 77% of the three facial reconstruction surfaces had <2.5 mm of error when compared to the relevant target face. The average error for each reconstruction was −0.46 mm (SD = 2.81) for A, −0.31 mm (SD = 2.40) for B, and −0.49 mm (SD = 2.16) for C. The facial features of the reconstructions demonstrated good levels of accuracy compared to the target faces. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the reproducibility of the soft tissue (ST) thicknesses at 31 landmarks using the cone-beam computed tomography (CBCT) images obtained from 20 adult subjects. Four observers carried out ST thickness measurements using Skull Measure software, and the inter- and intra-observer error rates were evaluated. Only five of 31 landmarks showed significant differences in recorded ST thickness between the observers. When excluding inexperienced observers, only one landmark showed a significant difference between the observers. Regarding the intra-observer reproducibility, the ST thickness measurements at three landmarks showed low correlation coefficients. The results of this study indicate that CBCT images can be used to measure ST thickness with high reproducibility. However, some landmarks need to be redefined to reliably measure ST thickness on CBCT images. [ABSTRACT FROM AUTHOR]

Abstract: All traditional CT reconstruction algorithms define the reconstruction slices as perpendicular to the axis of rotation. This leads to a significant inefficiency when reconstructing and visualizing multilayered planar objects such as stacked IC and MEMS devices. This paper reports an alternative solution to the planar CT reconstruction technologies that are published previously, based on a modified version of the widely used FDK cone-beam reconstruction algorithm. The present method distinguishes itself to the existing planar CT technologies and all other traditional CT reconstructions by defining the reconstruction slices along the exact orientation of the planar object in the scan. This new method still possesses the advantages of the previous planar CT technologies such as efficient reconstruction in terms of computation time and resources saving, higher reconstruction resolution in preferred direction, easy visualization, and so on. But it also has better performance than the existing ones by providing an analytical solution to the low-efficiency problem of the traditional FDK algorithm, further reducing the reconstruction volume, and eliminating the interpolation error induced by an image rotation process that is required by the previous planar CT methods. [Copyright &y& Elsevier]

Objectives: The accuracy of cone-beam technique, cone-beam computed tomography (CBCT), compared with that of the multislice spiral CT (MSCT), for image-based linear measurements of midpalatal suture was assessed. Material and Methods: Two measurements were performed by one investigator on the dry skull by using one digital caliper and in the axial cuts by using software. A 2D object-based image registration process was applied to determine the best affine transformation that maps a 2D input image (CBCT) in a reference image (MSCT). Results: The value of the intraclass correlation coefficient was approximately 0.9%. The results suggest that differences between two scanners did not exist (observation 1, p = 0.964 and observation 2, p = 0.795). With regard to the dry skull and the image, the significance probabilities equaled zero (observation 1, p = 0.002 and observation 2, p = 0.004), therefore, indicating significant differences. Conclusion: Measurements acquired in the images were similar and these findings contribute to stimulate the use of CBCT for evaluation of the maxillary expansion procedure. [ABSTRACT FROM AUTHOR]

Purpose: To determine the advantages and disadvantages of daily online adaptive image-guided radiotherapy (RT) compared with conventional RT for muscle-invasive bladder cancer. Methods and Materials: Twenty-seven patients with T2–T4 transitional cell carcinoma of the bladder were treated with daily online adaptive image-guided RT using cone-beam computed tomography (CBCT). From day 1 daily soft tissue–based isocenter positioning was performed using CBCT images acquired before treatment. Using a composite of the initial planning CT and the first five daily CBCT scans, small, medium, and large adaptive plans were created. Each of these adaptive plans used a 0.5-cm clinical target volume (CTV) to planning target volume expansion. For Fractions 8–32, treatment involved daily soft tissue–based isocenter positioning and selection of suitable adaptive plan of the day. Treating radiation therapists completed a credentialing program, and one radiation oncologist performed all the contouring. Comparisons were made between adaptive and conventional treatment on the basis of CTV coverage and normal tissue sparing. Results: All 27 patients completed treatment per protocol. Bladder volume decreased with time or fraction number (p < 0.0001). For the adaptive component (Fractions 8–32) the small, medium, large, and conventional plans were used in 9.8%, 49.2%, 39.5%, and 1.5% of fractions, respectively. For the adaptive strategy, 2.7% of occasions resulted in a CTV V95 <99%, compared with 4.8% of occasions for the conventional approach (p = 0.42). Mean volume of normal tissue receiving a dose >45 Gy was 29% (95% confidence interval, 24–35%) less with adaptive RT compared with conventional RT. The mean volume of normal tissue receiving >5 Gy was 15% (95% confidence interval, 11–18%) less with adaptive RT compared with conventional RT. Conclusions: Online adaptive radiotherapy is feasible in an academic radiotherapy center. The volume of normal tissue irradiated can be significantly smaller without reducing CTV coverage. [Copyright &y& Elsevier]

PURPOSE: To evaluate the reliability of the digital models scanned by cone-beam computed tomography (CBCT). METHODS: Forty plaster models of patients with orthodontic treatment were selected. These plaster models were scanned and measured by 3DX cone beam CT, compared with manual measurement via concordance correlation coefficient (CCC) and mean difference (MD). RESULTS: The CCC of all the measurement was from 0.847 to 0.993. The value of MD of all the measurement was below 0.25mm except CFF6, PWF5 and PWF6, which was 0.34mm, 0.63mm and 1.49mm, respectively. CONCLUSIONS: The reliability and accuracy of the digital models scanned by cone-beam CT is very high. The accuracy of measurement of the dental cusp is the highest, the dental fossa is the second, and the lowest point of palatal gingival is the third. Supported by Research Fund of Science and Technology Commission of Shanghai Municipality (08DZ2271100). [ABSTRACT FROM AUTHOR]

PURPUSE: To investigate the canal morphology of bilateral mandibular first premolar using cone-beam CT (CBCT). METHODS: Ninety-seven CBCT images of bilateral mandibular first premolar were selected . The images were analyzed with NNT software for the number and morphology of canal, groove, position of bifurcation and symmetry of bilateral canal classification. RESULTS: The canal configuration of mandibular first premolar was type I :83.5%, type III:3.6%, type V:8.8% and C-shaped canal:4.1% by Vertucci's classification. The incidence of groove in complicated canal (75%)was obviously higher than single canal (3.7%). 56.3% of complicated canal bifurcated in middle third, and 31.3% in apical third. 93.8% of mandibular first premolar had bilateral canal symmetry, the symmetry rate of single canal (95.2%) was higher than complicated canal (66.7%). CONCLUSIONS: CBCT can provide accurate information of canal system, the canal anatomy of mandibular first premolar is complex. Supported by Research Fund of Science and Technology Commission of Shanghai Municipality(08DZ2271100). [ABSTRACT FROM AUTHOR]

Circular cone-beam CT is one of the most popular configurations in both medical and industrial applications. The FDK algorithm is the most popular method for circular cone-beam CT. However, with increasing cone-angle the cone-beam artifacts associated with the FDK algorithm deteriorate because the circular trajectory does not satisfy the data sufficiency condition. Along with an experimental evaluation and verification, this paper proposed a curve-filtered FDK (C-FDK) algorithm. First, cone-parallel projections are rebinned from the native cone-beam geometry in two separate directions. C-FDK rebins and filters projections along different curves from T-FDK in the centrally virtual detector plane. Then, numerical experiments are done to validate the effectiveness of the proposed algorithm by comparing with both FDK and T-FDK reconstruction. Without any other extra trajectories supplemental to the circular orbit, C-FDK has a visible image quality improvement. [ABSTRACT FROM AUTHOR]

Abstract: Objective: DynaCT® is a method for obtaining computed tomography (CT)-like images using a C-arm system. Our aim was to compare the accuracy of these images to multidetector CT (MDCT) images prior to endovascular aortic repair (EVAR). Methods: A non-consecutive group of 20 elective patients were prospectively exposed to MDCT and one additional DynaCT before EVAR. Six arterial measurements and nine anatomical areas were chosen to: (1) visualise the peri-aortic soft tissue and assess the possibility to diagnose a potential haemorrhage from a ruptured aneurysm and (2) make the pre-treatment measurements before insertion of stent graft. Differences between modalities and readers were statistically compared using a linear mixed model. Results: For maximum aortic diameter, a significant difference of 1.3 mm was found between techniques (p = 0.043). Visibility scores were significantly better for all areas in MDCT data. Pre-treatment evaluation with DynaCT before EVAR was possible for all areas; evaluation of the iliac arteries were suboptimal due to a limited imaging volume size. Significant inter-reader differences were found for all anatomical areas. Conclusion: The result indicates that DynaCT gives sufficient information to determine the correct treatment and for selecting the proper stent graft before EVAR. A limited volume size reduces the evaluation of the iliac arteries. [Copyright &y& Elsevier]

Purpose: Knowing the anatomic location and also variations of the mandibular canal is especially important for surgical procedures on mandible such as dental implant surgery, impacted molar extraction and sagittal split ramus osteotomy. The purpose of this study was to clarify the incidence and location of bifid mandibular canals in an adult Turkish population to avoid complications during surgical procedures. Methods: A retrospective study using cone beam CT images was performed to evaluate bifid mandibular canal in mandible of 242 patients. Both right and left sides were studied ( n = 484). Axial, sagittal, cross-sectional and panoramic images were evaluated, and three-dimensional (3D) images were also reconstructed and evaluated, as necessary. The course and length of bifid mandibular canals and the superior and inferior angles between canals were measured. Results: Bifid mandibular canals were observed in 225 (46.5%) of 484 sides examined. The most frequently encountered type of bifid canal was the forward canal (29.80%), followed by the retromolar (28.10%) the buccolingual (14.50%) and the dental canal type (8.30%). Mean lengths of bifid canals were 13.6 mm in the right side and 14.1 mm in the left side. Mean superior angles were 139° on the right and 141° on the left side, whereas mean inferior angles were 38° on the right side and 32° on the left side. No statistically significant differences were found in the lengths or angles between the right and left sides and also for gender ( p < 0.05). Conclusions: This study, which utilized CBCT images, uncovered a higher prevalence of bifid mandibular canals than what has been reported in previous studies using conventional radiography techniques. [ABSTRACT FROM AUTHOR]

Abstract: Purpose: To study the inter- and intrafraction tumor reproducibility with active breath control (ABC) utilizing cone-beam computed tomography (CBCT), and compare validity of registration with two different regions of interest (ROI). Methods and materials: Thirty-one lung tumors in 19 patients received conventional or stereotactic body radiotherapy with ABC. During each treatment, patients had three CBCT scanned before and after online position correction and after treatment. These CBCT images were aligned to the planning CT using the gray scale registration of tumor and bony registration of the thorax, and tumor position uncertainties were then determined. Results: The interfraction systematic and random translation errors in the left–right (LR), superior–inferior (SI) and anterior–posterior (AP) directions were 3.6, 4.8, and 2.9mm; 2.5, 4.5, and 3.5mm, respectively, with gray scale alignment; 1.9, 4.3, 2.0mm and 2.5, 4.4, 2.9mm, respectively, with bony alignment. The interfraction systematic and random rotation errors with gray scale and bony alignment groups ranged from 1.4° to 3.0° and 0.8° to 2.3°, respectively. The intrafraction systematic and random errors with gray scale registration in LR, SI, AP directions were 0.9, 2.0, 1.8mm and 1.5, 1.7, 2.9mm, respectively, for translation; 1.5°, 0.9°, 1.0° and 1.2°, 2.2°, 1.8°, respectively, for rotation. The translational errors in SI direction with bony alignment were significantly larger than that of gray scale (p <0.05). Conclusions: With CBCT guided online correction the interfraction positioning errors can be markedly reduced. The intrafraction errors were not diminished by the use of ABC. Rotation errors were not very remarkable both inter- and intrafraction. Gray scale alignment of tumor may provide a better registration in SI direction. [Copyright &y& Elsevier]

PURPOSE: To investigate the anatomy of human maxillary sinus for providing some basic anatomical parameters related to sinus floor elevation and implant insertion. METHODS: A total of 40 cone-beam CT (CBCT) adults were selected and analyzed. The length (internal wall) and width of the maxillary sinus were measured, and the incidence and distribution of septa were investigated by use of three-dimensional reconstruction technique of CBCT. SPSS 11.0 software package was used for statistical analysis. RESULTS: The mean length (internal wall) and width of the maxillary. sinus were (30.1 ± :3.9) mm and (21.4±5.0) mm, respectively. There was no significant difference either in length or in width of maxillary sinus between males and females, or between right side and left side (P>0.05). Moreover, the incidence of sinus segments with septa was 53.8% (43/80). CONCLUSIONS: Base on this study, the use of CBCT is advantageous mandatory to avoid or reduce the incidence of surgical complications of maxillary sinus elevation. [ABSTRACT FROM AUTHOR]

Abstract: The demand of greater accuracy in intensity-modulated radiotherapy (IMRT) has driven the development of more advanced verification systems. The purpose of this study is to investigate the differences in verification accuracy in terms of the position error detected between cone-beam computed tomography (CBCT) and electronic portal imaging device (EPID) in the IMRT of nasopharyngeal carcinoma (NPC). Two groups of NPC patients (n = 22 and n = 28) verified by CBCT (G1-CB), EPID (G1-EP), and EPID (G2-EP) only, respectively, were recruited. The positional errors between the G1-CB group and the G2-EP group were compared. In addition, the magnitudes of the position errors of EPID taken in the same session of the CBCT, but after necessary corrections (G1-EP), were analyzed. In the CBCT group, 455 CBCT images (G1-CB) and 206 EPID images (G1-EP) were collected, whereas 319 EPID images (G2-EP) for the EPID group, were recorded. The median position errors detected in CBCT were between 0.80 and 0.90 mm in the antero-posterior (A-P), left-right (L-R), and supero-inferior (S-I) directions, whereas those of the EPID were all 0.50 mm. The magnitude of position deviation detected by the CBCT was higher than that of the EPID and their differences were extremely significant (p < 0.001). The frequencies in the G2-EP group with position errors greater than the tolerance (2 mm) were 32, 42, and 27 in the A-P, L-R, and S-I directions, respectively, which accounted for 16.5%, 21.6%, and 13.9% of the total number of EPID. There was difference in verification capability between the CBCT and EPID when applied to IMRT of NPC patients. Because an average of 1 of 6 verifications in EPID was inferior to that of the CBCT, verification by CBCT is recommended. [Copyright &y& Elsevier]

Purpose: To investigate buccal perimandibular neurovascularisation associated with the mandibular accessory buccal foramina (ABF) which were detected using a limited cone-beam computed tomography (limited CBCT). Methods: Five Japanese cadaveric mandibles had been examined using helical CT to investigate the presence or absence of ABF. Two mandibles indicating the presence of AMF were examined more minutely using a limited CBCT. Following the three-dimensional radiological observation of ABF, the mandibles were removed from the cadavers and dissected with referring to the findings of AMF on the limited CBCT images. Results: Four ABF of the three mandibular sides, which were depicted with limited CBCT, had different perimandibular neurovascularisation. Three accessory foramina were associated with the following arteries: a branch of the submental, facial, and buccal artery, and one was associated with a branch of the mental nerve. A branch of the mental nerve re-entered the mandible through the accessory foramen after it exited from a mental foramen. Conclusion: Limited CBCT is useful for pre-operative three-dimensional assessment of mandible since high-resolution analysis demonstrates not only the skeletal conditions but also the assessment and suggestions of perimandibular neurovascularisation. [ABSTRACT FROM AUTHOR]

Malunion after a distal radius fracture is very common and if symptomatic, is treated with a so-called corrective osteotomy. In a traditional distal radius osteotomy, the radius is cut at the fracture site and a wedge is inserted in the osteotomy gap to correct the distal radius pose. The standard procedure uses two orthogonal radiographs to estimate the two inclination angles and the dimensions of the wedge to be inserted into the osteotomy gap. However, optimal correction in 3-Dspace requires restoring three angles and three displacements. This paper introduces a new technique that uses preoperative planning based on 3-D images. Intraoperative 3-D imaging is also used after inserting pins with marker tools in the proximal and distal part of the radius and before the osteotomy. Positioning tools are developed to correct the distal radius pose in six degrees of freedom by navigating the pins. The method is accurate (derr < 1.2 mm, \varphi err < 0.9°, mTRE = 1.7 mm), highly reproducible (SE_d < 1.0 mm, SE_\varphi ≤ 1.4°, SE_mTRE = 0.7 mm), and allows intraoperative evaluation of the end result. Small incisions for pin placement and for the osteotomy render the method minimally invasive. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: The knowledge of root canal morphology and the existing anatomical variations is essential for successful endodontic therapy. Methods: This report presents an extraordinary case of unusual tooth morphology involving the bilateral existence of 7 maxillary and mandibular first and second molars with a single root and a single canal in a patient. Results: Endodontic retreatment of the affected teeth #15, #19, and #18 was performed. Cone-beam computed tomography (CBCT) images confirmed our diagnostic and therapeutic measures after endodontic management of the teeth. Conclusions: This morphologic variation has not been reported in the literature. The availability of 3-dimensional images further provided the opportunity for the precise description of the anatomy of 7 maxillary and mandibular molars with single roots and single canals. [ABSTRACT FROM AUTHOR]

Abstract: We report the setup reproducibility of thoracic and upper gastrointestinal (UGI) radiotherapy (RT) patients for 2 immobilization methods evaluated through cone-beam computed tomography (CBCT) image guidance, and present planning target volume (PTV) margin calculations made on the basis of these observations. Daily CBCT images from 65 patients immobilized in a chestboard (CB) or evacuated cushion (EC) were registered to the planning CT using automatic bony anatomy registration. The standardized region-of-interest for matching was focused around vertebral bodies adjacent to tumor location. Discrepancies >3 mm between the CBCT and CT datasets were corrected before initiation of RT and verified with a second CBCT to assess residual error (usually taken after 90 s of the initial CBCT). Positional data were analyzed to evaluate the magnitude and frequencies of setup errors before and after correction. The setup distributions were slightly different for the CB (797 scans) and EC (757 scans) methods, and the probability of adjustment at a 3-mm action threshold was not significantly different (p = 0.47). Setup displacements >10 mm in any direction were observed in 10% of CB fractions and 16% of EC fractions (p = 0.0008). Residual error distributions after CBCT guidance were equivalent regardless of immobilization method. Using a published formula, the PTV margins for the CB were L/R, 3.3 mm; S/I, 3.5 mm; and A/P, 4.6 mm), and for EC they were L/R, 3.7 mm; S/I, 3.3 mm; and A/P, 4.6 mm. In the absence of image guidance, the CB slightly outperformed the EC in precision. CBCT allows reduction to a single immobilization system that can be chosen for efficiency, logistics, and cost. Image guidance allows for increased geometric precision and accuracy and supports a corresponding reduction in PTV margin. [Copyright &y& Elsevier]

Abstract: A dog with a spontaneous maxillary tumour was given 40Gy of fractionated radiotherapy. At five out of 10 fractions cone-beam CT (CBCT) imaging before and after administration of an iodinated contrast agent were performed. Contrast enhancement maps were overlaid on the pre-contrast CBCT images. The tumour was clearly visualized in the images thus produced. [Copyright &y& Elsevier]

Computerized tomography (CT) forward projection is a simulation of CT data acquisition, which can not only be used to produce projection data, but also is a key part of the iterative algorithms for CT image reconstruction. The forward projection requires both excessive computation and time consuming in cone-beam scanning mode. For improving traditional forward projection algorithms, a graphics processing unit (GPU) based cone beam CT forward projection algorithm is proposed. The algorithm generates forward projection image rapidly by calculating the projections on detector of all X-rays in parallel. Since the algorithm supports the calculation at full floating point precision and adopts tri-linear interpolation, the high-precision projection image can be achieved. The advantages of this algorithm were verified by the experiments of the projection calculation of Shepp-Logan phantom and by the comparison with other forward projection algorithms. [ABSTRACT FROM AUTHOR]

Purpose: Cone-beam computed tomographic images (CBCTs) are increasingly used for setup correction, soft tissue targeting, and image-guided adaptive radiotherapy. However, CBCT image quality is limited by low contrast and imaging artifacts. This analysis investigates the detectability of soft tissue boundaries in CBCT by performing a multiple-observer segmentation study. Methods and Materials: In four prostate cancer patients prostate, bladder and rectum were repeatedly delineated by five observers on CBCTs and fan-beam CTs (FBCTs). A volumetric analysis of contouring variations was performed by calculating coefficients of variation (COV: standard deviation/average volume). The topographical distribution of contouring variations was analyzed using an average surface mesh-based method. Results: Observer- and patient-averaged COVs for FBCT/CBCT were 0.09/0.19 for prostate, 0.05/0.08 for bladder, and 0.09/0.08 for rectum. Contouring variations on FBCT were significantly smaller than on CBCT for prostate (p < 0.03) and bladder (p < 0.04), but not for rectum (p < 0.37; intermodality differences). Intraobserver variations from repeated contouring of the same image set were not significant for either FBCT or CBCT (p < 0.05). Average standard deviations of individual observers'' contour differences from average surface meshes on FBCT vs. CBCT were 1.5 vs. 2.1 mm for prostate, 0.7 vs. 1.4 mm for bladder, and 1.3 vs. 1.5 mm for rectum. The topographical distribution of contouring variations was similar for FBCT and CBCT. Conclusion: Contouring variations were larger on CBCT than FBCT, except for rectum. Given the well-documented uncertainty in soft tissue contouring in the pelvis, improvement of CBCT image quality and establishment of well-defined soft tissue identification rules are desirable for image-guided radiotherapy. [Copyright &y& Elsevier]

This paper presents a fast hybrid CPU- and GPU-based CT reconstruction algorithm to reduce the amount of back-projection operation using air skipping involving polygon clipping. The algorithm easily and rapidly selects air areas that have significantly higher contrast in each projection image by applying K-means clustering method on CPU, and then generates boundary tables for verifying valid region using segmented air areas. Based on these boundary tables of each projection image, clipped polygon that indicates active region when back-projection operation is performed on GPU is determined on each volume slice. This polygon clipping process makes it possible to use smaller number of voxels to be back-projected, which leads to a faster GPU-based reconstruction method. This approach has been applied to a clinical data set and Shepp-Logan phantom data sets having various ratio of air region for quantitative and qualitative comparison and analysis of our and conventional GPU-based reconstruction methods. The algorithm has been proved to reduce computational time to half without losing any diagnostic information, compared to conventional GPU-based approaches. [ABSTRACT FROM AUTHOR]

Purpose: To assess imaging dose of partial and full-angle kilovoltage CBCT scan protocols and to evaluate image quality for each protocol. Methods: The authors obtained the CT dose index (CTDI) of the kilovoltage CBCT protocols in an on-board imager by ion chamber (IC) measurements and Monte Carlo (MC) simulations. A total of six new CBCT scan protocols were evaluated: Standard-dose head (100 kVp, 151 mA s, partial-angle), low-dose head (100 kVp, 75 mA s, partial-angle), high-quality head (100 kVp, 754 mA s, partial-angle), pelvis (125 kVp, 706 mA s, full-angle), pelvis spotlight (125 kVp, 752 mA s, partial-angle), and low-dose thorax (110 kVp, 271 mA s, full-angle). Using the point dose method, various CTDI values were calculated by (1) the conventional weighted CTDI (CTDIw) calculation and (2) Bakalyar’s method (CTDIwb). The MC simulations were performed to obtain the CTDIw and CTDIwb, as well as from (3) central slice averaging (CTDI2D) and (4) volume averaging (CTDI3D) techniques. The CTDI values of the new protocols were compared to those of the old protocols (full-angle CBCT protocols). Image quality of the new protocols was evaluated following the CBCT image quality assurance (QA) protocol [S. Yoo et al., “A quality assurance program for the on-board imager®,” Med. Phys. 33(11), 4431–4447 (2006)] testing Hounsfield unit (HU) linearity, spatial linearity/resolution, contrast resolution, and HU uniformity. Results: The CTDIw were found as 6.0, 3.2, 29.0, 25.4, 23.8, and 7.7 mGy for the new protocols, respectively. The CTDIw and CTDIwb differed within +3% between IC measurements and MC simulations. Method (2) results were within ±12% of method (1). In MC simulations, the CTDIw and CTDIwb were comparable to the CTDI2D and CTDI3D with the differences ranging from -4.3% to 20.6%. The CTDI3D were smallest among all the CTDI values. CTDIw of the new protocols were found as ∼14 times lower for standard head scan and 1.8 times lower for standard body scan than the old protocols, respectively. In the image quality QA tests, all the protocols except low-dose head and low-dose thorax protocols were within the tolerance in the HU verification test. The HU value for the two protocols was always higher than the nominal value. All the protocols passed the spatial linearity/resolution and HU uniformity tests. In the contrast resolution test, only high-quality head and pelvis scan protocols were within the tolerance. In addition, crescent effect was found in the partial-angle scan protocols. Conclusions: The authors found that CTDIw of the new CBCT protocols has been significantly reduced compared to the old protocols with acceptable image quality. The CTDIw values in the point dose method were close to the volume averaging method within 9%–21% for all the CBCT scan protocols. The Bakalyar’s method produced more accurate dose estimation within 14%. The HU inaccuracy from low-dose head and low-dose thorax protocols can render incorrect dose results in the treatment planning system. When high soft-tissue contrast data are desired, high-quality head or pelvis scan protocol is recommended depending on the imaging area. The point dose method can be applicable to estimate CBCT dose with reasonable accuracy in the clinical environment. [ABSTRACT FROM AUTHOR]

Cleidocranial dysplasia (CCD) is a rare congenital disorder with prolonged retention of the primary teeth, unerupted permanent teeth, and supernumerary teeth. We report a 19-year-old well-developed and well-nourished Thai woman who presented with intermittent dull pain in the lower left jaw for about a week. CCD was diagnosed based on a panoramic radiograph that revealed 32 unerupted teeth affecting all four quadrants of her jaw. Chest and skull radiographs were added to evaluate the clavicles and skull bone formation to confirm the diagnosis of CCD. Family members, including parents and siblings, were radiographically investigated and showed no abnormality. After a 6-h first operation in the lower left jaw to remove five supernumerary teeth, a deciduous canine, and a permanent third molar, three-dimensional imaging by cone-beam computed tomography was conducted as an aid for planning further dental surgery and orthodontic treatment. A second operation was conducted to remove the other unerupted teeth in the four quadrants in 6 h, the same as the initial operation time, although the second involved the whole jaw, as compared with the first operation in only one quadrant. [ABSTRACT FROM AUTHOR]

Purpose: Anatomical background presents a major impediment to detectability in 2D radiography as well as 3D tomosynthesis and cone-beam CT (CBCT). This article incorporates theoretical and experimental analysis of anatomical background “noise” in cascaded systems analysis of 2D and 3D imaging performance to yield “generalized” metrics of noise-equivalent quanta (NEQ) and detectability index as a function of the orbital extent of the (circular arc) source-detector orbit. Methods: A physical phantom was designed based on principles of fractal self-similarity to exhibit power-law spectral density (κ/fβ) comparable to various anatomical sites (e.g., breast and lung). Background power spectra [SB(f)] were computed as a function of source-detector orbital extent, including tomosynthesis (∼10°–180°) and CBCT (180°+fan to 360°) under two acquisition schemes: (1) Constant angular separation between projections (variable dose) and (2) constant total number of projections (constant dose). The resulting SB was incorporated in the generalized NEQ, and detectability index was computed from 3D cascaded systems analysis for a variety of imaging tasks. Results: The phantom yielded power-law spectra within the expected spatial frequency range, quantifying the dependence of clutter magnitude (κ) and correlation (β) with increasing tomosynthesis angle. Incorporation of SB in the 3D NEQ provided a useful framework for analyzing the tradeoffs among anatomical, quantum, and electronic noise with dose and orbital extent. Distinct implications are posed for breast and chest tomosynthesis imaging system design—applications varying significantly in κ and β, and imaging task and, therefore, in optimal selection of orbital extent, number of projections, and dose. For example, low-frequency tasks (e.g., soft-tissue masses or nodules) tend to benefit from larger orbital extent and more fully 3D tomographic imaging, whereas high-frequency tasks (e.g., microcalcifications) require careful, application-specific selection of orbital extent and number of projections to minimize negative effects of quantum and electronic noise. Conclusions: The complex tradeoffs among anatomical background, quantum noise, and electronic noise in projection imaging, tomosynthesis, and CBCT can be described by generalized cascaded systems analysis, providing a useful framework for system design and optimization. [ABSTRACT FROM AUTHOR]

Purpose: To quantify diaphragm motion in megavoltage (MV) cone-beam computed tomography (CBCT) projections. Methods: User identified ipsilateral hemidiaphragm apex (IHDA) positions in two full exhale and inhale frames were used to create bounding rectangles in all other frames of a CBCT scan. The bounding rectangle was enlarged to create a region of interest (ROI). ROI pixels were associated with a cost function: The product of image gradients and a gradient direction matching function for an ideal hemidiaphragm determined from 40 training sets. A dynamic Hough transform (DHT) models a hemidiaphragm as a contour made of two parabola segments with a common vertex (the IHDA). The images within the ROIs are transformed into Hough space where a contour’s Hough value is the sum of the cost function over all contour pixels. Dynamic programming finds the optimal trajectory of the common vertex in Hough space subject to motion constraints between frames, and an active contour model further refines the result. Interpolated ray tracing converts the positions to room coordinates. Root-mean-square (RMS) distances between these positions and those resulting from an expert’s identification of the IHDA were determined for 21 Siemens MV CBCT scans. Results: Computation time on a 2.66 GHz CPU was 30 s. The average craniocaudal RMS error was 1.38±0.67 mm. While much larger errors occurred in a few near-sagittal frames on one patient’s scans, adjustments to algorithm constraints corrected them. Conclusions: The DHT based algorithm can compute IHDA trajectories immediately prior to radiation therapy on a daily basis using localization MVCBCT projection data. This has potential for calibrating external motion surrogates against diaphragm motion. [ABSTRACT FROM AUTHOR]

Abstract: This preliminary retrospective study evaluates the diagnostic value of cone-beam computed tomography (CBCT), as a potential standard preoperative procedure, in assessing mandibular invasion by oral squamous cell carcinoma (OSCC) compared with conventional preoperative panoramic radiography (PR), magnetic resonance imaging (MRI) and histological examination of the resection specimen (the golden standard). Between September 2006 and September 2009, 23 patients with histology proven primary OSCC, adjacent to or fixed to the mandible were included. The tumours were classified into four groups, ranging from no bone invasion to evident bone invasion. Sensitivity and specificity for PR were 55% (95% CI [0.350;0.619]) and 92% (95% CI 0.737;0.984]), respectively, both were significantly lower than the 91% (95% CI [0.740;0.909]) and 100% (95% CI [0.845;1]), respectively, for CBCT. MRI showed 82% sensitivity (95% CI [0.608;0.941]) and 67% specificity (95% CI [0.474;0.779]). CBCT has the potential to become a new diagnostic tool in the OSCC screening procedure to predict mandibular invasion or erosion, but its value may be limited by its relatively low sensitivity. A prospective study will start on 64 patients (α =0.05; power 0.8; effect size 0.5) to improve these results statistically. [Copyright &y& Elsevier]

Abstract: Purpose: To investigate setup discrepancies measured with ExacTrac X-ray 6 degree-of-freedom (6D) and cone-beam computed tomography (CBCT) for patients under treatments of stereotactic body radiation therapy (SBRT). Materials and methods: In this work, phantom and patient studies were performed. In the phantom studies, an anthropomorphic phantom was placed with pre-defined positions, and imaged with ExacTrac X-ray 6D and CBCT to test the accuracy of the imaging systems. In the patient studies, 16 spinal SBRT patient cases were retrospectively analyzed. The patients were initially positioned in customized immobilization cradles and then aligned with ExacTrac X-ray 6D and CBCT. The setup discrepancies were computed and quantitatively analyzed. Results: This study indicates modest discrepancies between ExacTrac X-ray 6D and CBCT with spinal SBRT. The phantom experiments showed that translational and rotational discrepancies in root-mean-square (RMS) between ExacTrac X-ray 6D and CBCT were, respectively, <1.0mm and <1°. In the retrospective patient studies, translational and rotational discrepancies in RMS between ExacTrac X-ray 6D and CBCT were <2.0mm and <1.5°. Conclusions: ExacTrac X-ray 6D represents a potential alternative to CBCT; however, pre-caution should be taken when only ExacTrac X-ray 6D is used to guide SBRT with small setup margins. [Copyright &y& Elsevier]

Purpose: To prospectively compare setup error in standard thermoplastic masks and skin-sparing masks (SSMs) modified with low neck cutouts for head-and-neck intensity-modulated radiation therapy (IMRT) patients. Methods and Materials: Twenty head-and-neck IMRT patients were randomized to be treated in a standard mask (SM) or SSM. Cone-beam computed tomography (CBCT) scans, acquired daily after both initial setup and any repositioning, were used for initial and residual interfraction evaluation, respectively. Weekly, post-IMRT CBCT scans were acquired for intrafraction setup evaluation. The population random (σ) and systematic (Σ) errors were compared for SMs and SSMs. Skin toxicity was recorded weekly by use of Radiation Therapy Oncology Group criteria. Results: We evaluated 762 CBCT scans in 11 patients randomized to the SM and 9 to the SSM. Initial interfraction σ was 1.6 mm or less or 1.1° or less for SM and 2.0 mm or less and 0.8° for SSM. Initial interfraction Σ was 1.0 mm or less or 1.4° or less for SM and 1.1 mm or less or 0.9° or less for SSM. These errors were reduced before IMRT with CBCT image guidance with no significant differences in residual interfraction or intrafraction uncertainties between SMs and SSMs. Intrafraction σ and Σ were less than 1 mm and less than 1° for both masks. Less severe skin reactions were observed in the cutout regions of the SSM compared with non-cutout regions. Conclusions: Interfraction and intrafraction setup error is not significantly different for SSMs and conventional masks in head-and-neck radiation therapy. Mask cutouts should be considered for these patients in an effort to reduce skin toxicity. [Copyright &y& Elsevier]

Objective: To evaluate systematic differences in landmark position between cone-beam computed tomography (CBCT)-generated cephalograms and conventional digital cephalograms and to estimate how much variability should be taken into account when both modalities are used within the same longitudinal study. Materials and Methods: Landmarks on homologous cone-beam computed tomographic- generated cephalograms and conventional digital cephalograms of 46 patients were digitized, registered, and compared via the Hotelling T2 test. Results: There were no systematic differences between modalities in the position of most landmarks. Three landmarks showed statistically significant differences but did not reach clinical significance. A method for error calculation while combining both modalities in the same individual is presented. Conclusion: In a longitudinal follow-up for assessment of treatment outcomes and growth of one individual, the error due to the combination of the two modalities might be larger than previously estimated. [ABSTRACT FROM AUTHOR]