Cone-beam Computed Tomography Acquisition Research Articles

Machine log file-based dose verification using novel iterative CBCT reconstruction algorithm in commercial software during volumetric modulated arc therapy for prostate cancer patients.

To evaluate the utility of the use of iterative cone-beam computed tomography (CBCT) for machine log file-based dose verification during volumetric modulated arc therapy (VMAT) for prostate cancer patients. All CBCT acquisition data were used to reconstruct images with the Feldkamp-Davis-Kress algorithm (FDK-CBCT) and the novel iterative algorithm (iCBCT). The Hounsfield unit (HU)-electron density curves for CBCT images were created using the Advanced Electron Density Phantom. The I'mRT and anthropomorphic phantoms were irradiated with VMAT after CBCT registration. Subsequently, fourteen prostate cancer patients received VMAT after CBCT registration. Machine log files and both CBCT images were exported to the PerFRACTION software, and a 3D patient dose was reconstructed. Mean dose for planning target volume (PTV), the bladder, and rectum and the 3D gamma analysis were evaluated. For the phantom studies, the variation of HU values was observed at the central position surrounding the bones in FDK-CBCT. There were almost no changes in the difference of doses at the isocenter between measurement and reconstructed dose for planning CT (pCT), FDK-CBCT, and iCBCT. Mean dose differences of PTV, rectum, and bladder between iCBCT and pCT were approximately 2% lower than those between FDK-CBCT and pCT. For the clinical study, average gamma analysis for 2%/2 mm was 98.22% ± 1.07 and 98.81% ± 1.25% in FDK-CBCT and iCBCT, respectively. A similar machine log file-based dose verification accuracy is obtained for FDK-CBCT and iCBCT during VMAT for prostate cancer patients.

Augmented reality navigation for cranial biopsy and external ventricular drain insertion.

The aim of this study was to evaluate the accuracy (deviation from the target or intended path) and efficacy (insertion time) of an augmented reality surgical navigation (ARSN) system for insertion of biopsy needles and external ventricular drains (EVDs), two common neurosurgical procedures that require high precision. The hybrid operating room-based ARSN system, comprising a robotic C-arm with intraoperative cone-beam CT (CBCT) and integrated video tracking of the patient and instruments using nonobtrusive adhesive optical markers, was used. A 3D-printed skull phantom with a realistic gelatinous brain model containing air-filled ventricles and 2-mm spherical biopsy targets was obtained. After initial CBCT acquisition for target registration and planning, ARSN was used for 30 cranial biopsies and 10 EVD insertions. Needle positions were verified by CBCT. The mean accuracy of the biopsy needle insertions (n = 30) was 0.8 mm ± 0.43 mm. The median path length was 39 mm (range 16-104 mm) and did not correlate to accuracy (p = 0.15). The median device insertion time was 149 seconds (range 87-233 seconds). The mean accuracy for the EVD insertions (n = 10) was 2.9 mm ± 0.8 mm at the tip with a 0.7° ± 0.5° angular deviation compared with the planned path, and the median insertion time was 188 seconds (range 135-400 seconds). This study demonstrated that ARSN can be used for navigation of percutaneous cranial biopsies and EVDs with high accuracy and efficacy.

Comparison of the expression of the volumetric alteration artifact in cylindrical and triangular fields of view in two cone-beam computed tomography devices.

To compare the expression of the volumetric alteration (VA) artifact between cylindrical and convex triangular fields of view (FOVs) using high-density materials in different positions in two cone-beam computed tomography (CBCT) devices. Cylinders of five high-density materials (amalgam, chromium-cobalt, gutta-percha, titanium, and zirconium) with known physical volume were individually submitted to CBCT acquisition in four positions inside a polymethylmethacrylate phantom using two different FOV shapes (convex triangular and cylindrical) on the Veraviewepocs® R100 (R100) and Veraview® X800 (X800) devices. Two oral radiologists obtained the tomographic volumes by segmenting each cylinder. The difference between the tomographic and physical volumes corresponded to the VA. These values were analyzed by intraclass correlation coefficient and analysis of variance for repeated measures with Tukey post hoc test (α = 5%). The FOV influenced the VA only in the X800 device (p = 0.014): the VA in the triangular FOV was greater than in the cylindrical FOV. The VA in the triangular FOV of the X800 device was greater than the R100 device (p < 0.0001). The material influenced the expression of the VA only in the R100 device (p < 0.0001); gutta-percha presented the highest VA, being underestimated, and differing from the other materials (p < 0.01). The triangular FOV increased the VA of high-density materials in the X800 device. It is important to know if there is an influence on the volumetric alteration artifact of dental materials due to the different image formation geometry in the convex triangular FOV.

Image-Guided Surgical Simulation in Minimally Invasive Liver Procedures: Development of a Liver Tumor Porcine Model Using a Multimodality Imaging Assessment.

Background: Image-guided liver surgery and interventions are growing as part of the current trend to translate liver procedures into minimally invasive approaches. Hands-on surgical training in such techniques is required. Consequently, a meaningful and realistic liver tumor model using multi-imaging modalities, such as ultrasound (US), computed tomography (CT), magnetic resonance (MR), cone beam-CT (CBCT), is mandatory. The first aim of this study is to develop a novel tumor-mimic model and assess it with multi-imaging modalities. The second aim is to evaluate the usefulness of the model during image-guided liver procedures. Materials and Methods: The tumor-mimic model is made of a composition of hydrogel, smashed muscle, and gadolinium contrast solution. Five ex vivo livers and three pigs were included in the study. Procedures were performed in an experimental hybrid operating room. Under general anesthesia, US guidance was required to inject the biotumor formula into the pig's liver. US, CT, CBCT, and MR acquisitions were then performed after the initial injection. In vivo models were then used to perform liver procedures, including US-guided biopsy, radiofrequency ablation, and laparoscopic resection. Results: The formula developed is easily injected generating a tissue-like material. Visualization using multi-imaging modalities was appropriate, thereby allowing to perform image-guided techniques. Conclusion: A novel design of an in vivo and ex vivo tissue-like tumor liver model is presented. Due to the multimodality imaging appraisal, it may provide a realistic and meaningful model allowing to perform image-guided liver procedures.

Impact of Acquisition Protocols on Accuracy of Dose Calculation Based on XVI Cone Beam Computed Tomography.

Purpose:The objective of this work is to study the impact of acquisition protocols on the accuracy of cone beam computed tomography (CBCT)-based dose calculation and to determinate its limits from image characteristics such as image quality, Hounsfield numbers consistency, and restrictive sizes of volume acquisition, compared to the CT imaging for the different anatomy localizations: head and neck (H&N), thorax, and pelvis.Materials and Methods:In this work, we used a routine on-board imaging CBCT of the XVI system (Elekta, Stockholm, Sweden). Dosimetric calculations performed on CT images require the knowledge of the Hounsfield unit-relative electron density (HU-ReD) calibration curve, which is determined for each imaging technology and must be adapted to the imaging acquisition parameters (filter/field of view). The accuracy of the dose calculation from CBCT images strongly depends on the quality of these images and also on the appropriate correspondence to the electronic densities, which will be used by the treatment planning system to simulate the dose distribution. In this study, we evaluated the accuracy of the dose calculation for each protocol, as already pointed in many studies.Results:As a result, the protocols that give better results in terms of dose calculation are F0S20 for the H&N region and F1M20 for the thoracic and pelvic regions, with an error <2% compared to results obtained with CT images. In addition, the dose distributions obtained with CT and CBCT imaging modalities were compared by two different methods. The first comparison was done by gamma index in three planes (sagittal, coronal, and transverse) with 2%; 2 mm criteria. The results showed good correspondence, with more than 95% of points passed the criteria. We also compared the target volume, the organs at risk (OARs), and the maximum and minimum doses for the three localizations (H&N, thorax, and pelvis) in CT and CBCT imaging modalities using a Rando phantom.Conclusions:The choice of the adequate CBCT acquisition protocol and the appropriate phantom to determine the HU-ReD calibration curve provides a better precision in the calculation of dose on CBCT images. This allows improving the results obtained when using the HU-ReD calibration method for dose calculation in adaptive radiotherapy.

Quantitative Analysis of the Treatment Set Up Reliability of a Prone Breast Boost for Early Stage Breast Cancer

Adjuvant whole-breast radiation and a tumor bed boost for early-stage breast cancer can be delivered in the supine or prone position. Delivering the boost in the prone position has the advantage of removing the supine simulation CT and the capability of obtaining the total treatment dose distribution. However, the reliability of daily prone boost set up is largely unknown, and imaging is used for treatment verification. Here we evaluate the reliability of a daily clinical setup protocol for a prone mini-tangent boost, using daily cone beam CT (CBCT) to verify the adequacy of target coverage. We retrospectively reviewed 13 patients treated with a prone mini-tangent boost. The target (CTV) was the tumor bed without further expansion. Distance from CTV to block edge was 1.5cm. The boost prescription was 10Gy in 5 fractions. Coverage goals were the treating physician’s discretion, However, in all cases the planned dose to 90% of the CTV (D90) > 90% of prescription. Patients were positioned daily using a clinical setup with visual verification. Port films were taken to verify day 1 setup and when there was concern about the daily clinical setup. A CBCT was then acquired. If needed, additional shifts were made based on the CBCT, often followed by port films. Retrospectively, the simulation CT was independently registered to the daily CBCTs by a physician, and a daily tumor bed contour was generated. The treatment plan was transferred to the daily CBCT and delivered dose was calculated. To assess the reliability of clinical setup prior to CBCT acquisition, we assessed how often the daily D90 was < 90% of prescription dose (D90 < 90%) and how often the daily volume receiving full prescription dose (V100daily) did not receive the planned V100 (V100plan) by > 10% (V100plan-V100daily > 10%). Twelve patients with full imaging details were analyzed. Of 60 analyzable daily fractions, D90 < 90% for 3/60 fractions (5%), and V100plan-V100daily > 10% for 11/60 fractions (18%). Post-CBCT shifts were made for 1 fraction with D90 < 90% and for 2 fractions with V100plan-V100daily > 10%. Fractions for which coverage did not meet reliability metrics most commonly involved superficial tumor beds that extended into the region of subcutaneous dose build-up. In all such cases, allowing a portion of the target to receive less than prescription dose was deemed acceptable by the treating physician. We found that a daily clinical treatment setup for a prone boost was reliable in most cases. Addition of a CBCT was helpful to identify clinical setup variability. Treatment of a superficial tumor bed may be more sensitive to small variations in daily treatment setup due to the dose gradient across the target. When superficial target coverage is critical, supine boost positioning may be considered.

CBCT image quality QA: Establishing a quantitative program.

PurposeRoutine quality assurance (QA) of cone‐beam computed tomography (CBCT) scans used for image‐guided radiotherapy is prescribed by the American Association of Physicists in Medicine Task Group (TG)‐142 report. For CBCT image quality, TG‐142 recommends using clinically established baseline values as QA tolerances. This work examined how image quality parameters vary both across machines of the same model and across different CBCT techniques. Additionally, this work investigated how image quality values are affected by imager recalibration and repeated exposures during routine QA.MethodsCone‐beam computed tomography scans of the Catphan 604 phantom were taken on four TrueBeam® and one Edge™ linear accelerator using four manufacturer‐provided techniques. TG‐142 image quality parameters were calculated for each CBCT scan using SunCHECK Machine™. The variability of each parameter with machine and technique was evaluated using a two‐way ANOVA test on a dataset consisting of 200 CBCT scans. The impact of imager calibration on image quality parameters was examined for a subset of three machines using an unpaired Student’s t‐test. The effect of artifacts appearing on CBCTs taken in rapid succession was characterized and an approach to reduce their appearance was evaluated. Additionally, a set of baselines and tolerances for all image quality metrics was presented.ResultsAll imaging parameters except geometric distortion varied with technique (P < 0.05) and all imaging parameters except slice thickness varied with machine (P < 0.05). Imager calibration can change the expected value of all imaging parameters, though it does not consistently do so. While changes are statistically significant, they may not be clinically significant. Finally, rapid acquisition of CBCT scans can introduce image artifacts that degrade CBCT uniformity.ConclusionsThis work characterized the variability of acquired CBCT data across machines and CBCT techniques along with the impact of imager calibration and rapid CBCT acquisition on image quality.

Development of a model of soft tissue simulation using ballistic gelatin for CBCT acquisitions related to dentomaxillofacial radiology research.

To present the ballistic gelatin as a new material capable of simulating the soft tissues in cone-beam CT (CBCT) images. CBCT images of three piglet heads were acquired with their soft tissues intact (standard group). Subsequently, the piglet heads were fixed in a container using metallic pins and moulded with acrylic resin; the soft tissues were then removed and replaced by ballistic gelatin, with the same thickness of the original soft tissues. The images were evaluated by two oral radiologists, to check the adaptation on bone surfaces, thickness and density, penetration into large bone cavities and cancellous bone, and the presence of air bubbles using a 5-score scale. Additionally, an objective analysis was carried out by one oral radiologist. For each CBCT scan, three axial reconstructions were selected to represent the mandibular, occlusal, and maxillary levels. The mean and standard deviation (SD) of the grey values were calculated in four regions of interest determined on soft tissue areas and compared by two-way ANOVA. The ballistic gelatin showed subjective scores ranging from good to excellent for all parameters evaluated. There was no significant difference in the mean and SD values of the grey values between ballistic gelatin and the gold standard groups for all levels (p > 0.05). Higher SD values were observed in the occlusal level for both groups (p < 0.05). Ballistic gelatin has visual and objective similarity with the gold standard. Thus, the ballistic gelatin is a promising material capable of simulating soft tissues in CBCT images.

Patient-based low dose cone beam CT acquisition settings for prostate image-guided radiotherapy treatments on a Varian TrueBeam linear accelerator.

To evaluate the performance of low dose cone beam CT (CBCT) acquisition protocols for image-guided radiotherapy of prostate cancer. CBCT images of patients undergoing prostate cancer radiotherapy were acquired with the settings currently used in our department and two low dose settings at 50% and 63% lower exposure. Four experienced radiation oncologists and two radiation therapy technologists graded the images on five image quality characteristics. The scores were analysed through Visual Grading Regression, using the acquisition settings and the patient size as covariates. The low dose acquisition settings have no impact on the image quality for patients with body profile length at hip level below 100 cm. A reduction of about 60% of the dose is feasible for patients with size below 100 cm. The visibility of low contrast features can be compromised if using the low dose acquisition settings for patients with hip size above 100 cm. Low dose CBCT acquisition protocols for the pelvis, based on subjective evaluation of patient images.

Visualization of flow diverter stent wall apposition during intracranial aneurysm treatment using a virtually diluted cone beam CT technique (Vessel ASSIST)

Flow diverters (FD) have poor radiopacity, challenging visualization of deployment and vessel wall apposition with conventional neuroimaging modalities. We evaluated a novel cone beam computed tomography (CT) imaging technique that allows virtual dilution (VD) of contrast media to facilitate workflow and ensure accurate assessment of FD wall apposition. We retrospectively evaluated all patients treated for intracranial aneurysms with FD at our institution between November 2018 and November 2019. Undiluted injected dual cone beam CT acquisitions performed post-stenting were displayed with VD software (GE Healthcare). The resulting images were compared with conventional two-dimensional (2D) digital subtraction angiography (DSA) images. Two neurointerventionalists (Reader 1 and Reader 2, (R1, R2)) independently assessed FD deployment and wall apposition. Confidence in the diagnosis, inter-reader agreement, and X-ray exposure were assessed. A total of 27 cases were reviewed. FD deployment and wall apposition scores were 4.2 ± 1.0 (R1) and 4.0 ± 1.1 (R2) for DSA and 3.7 ± 1.2 (R1) and 4.1 ± 1.0 (R2) for VD. Confidence in the diagnosis was improved with VD, with scores of 3.7 ± 0.7 (R1) and 4.0 ± 0.7 (R2) using DSA and 4.9 ± 0.2 (R1) and 4.9 ± 0.2 (R2) using VD (P < 0.001). Inter-reader agreement using 2D DSA was improved from moderate (0.49324) to good (0.7272) (P < 0.0001). There were no significant differences in inter-reader agreement in the deployment assessment (P = 0.68) or dose-area product (P = 0.54) between techniques. VD imaging with dual cone beam CT enables accurate assessment of FD wall apposition after deployment with greater confidence and improved inter-reader agreement versus conventional 2D DSA alone, with comparable X-ray exposure.

A Monte Carlo based scatter removal method for non-isocentric cone-beam CT acquisitions using a deep convolutional autoencoder

The primary cone-beam computed tomography (CBCT) imaging beam scatters inside the patient and produces a contaminating photon fluence that is registered by the detector. Scattered photons cause artifacts in the image reconstruction, and are partially responsible for the inferior image quality compared to diagnostic fan-beam CT. In this work, a deep convolutional autoencoder (DCAE) and projection-based scatter removal algorithm were constructed for the ImagingRingTM system on rails (IRr), which allows for non-isocentric acquisitions around virtual rotation centers with its independently rotatable source and detector arms. A Monte Carlo model was developed to simulate (i) a non-isocentric training dataset of ≈1200 projection pairs (primary + scatter) from 27 digital head-and-neck cancer patients around five different virtual rotation centers (DCAENONISO), and (ii) an isocentric dataset existing of ≈1200 projection pairs around the physical rotation center (DCAEISO). The scatter removal performance of both DCAE networks was investigated in two digital anthropomorphic phantom simulations and due to superior performance only the DCAENONISO was applied on eight real patient acquisitions. Measures for the quantitative error, the signal-to-noise ratio, and the similarity were evaluated for two simulated digital head-and-neck patients, and the contrast-to-noise ratio (CNR) was investigated between muscle and adipose tissue in the real patient image reconstructions. Image quality metrics were compared between the uncorrected data, the currently implemented heuristic scatter correction data, and the DCAE corrected image reconstruction. The DCAENONISO corrected image reconstructions of two digital patient simulations showed superior image quality metrics compared to the uncorrected and corrected image reconstructions using a heuristic scatter removal. The proposed DCAENONISO scatter correction in this study was successfully demonstrated in real non-isocentric patient CBCT acquisitions and achieved statistically significant higher CNRs compared to the uncorrected or the heuristic corrected image data. This paper presents for the first time a projection-based scatter removal algorithm for isocentric and non-isocentric CBCT imaging using a deep convolutional autoencoder trained on Monte Carlo composed datasets. The algorithm was successfully applied to real patient data.

Effective doses of dental cone beam computed tomography: effect of 360-degree versus 180-degree rotation angles

The aims of this study were to compare radiation absorbed dose (AD) and effective dose (ED) to tissues from cone beam computed tomography (CBCT) scans with 360-degree versus 180-degree rotations with use of different fields of view (FOV), to compare EDs calculated from measured ADs versus dose area product (DAP) values, and to compare doses to the lens of the eye (LOE) from different scan parameters. ADs for each protocol were measured in tissues, including the LOE, by using an anthropometric phantom. EDs were calculated on the basis of dosimetry (EDm) and DAP values (EDd). Dose differences were determined with analysis of variance (ANOVA). ADs and EDs were substantially lower for 180-degree rotation scans compared with 360-degree rotation scans (P < .01). Remainder tissues had the greatest effect on effective dose for most FOVs. Doses were generally lower with small FOVs compared with large FOVs. Most EDm values were lower than EDd values in large FOVs but higher in small FOVs. Differences in EDm and EDd were variable and unpredictable. LOE doses were smaller with the 180-degree scans and smaller FOVs. Radiation doses were generally lower with 180-degree rotation scans and smaller FOVs. These parameters should be used for CBCT acquisitions, whenever possible, and should be made available in all units.

Image retake rates of cone beam computed tomography in a dental institution.

To investigate the frequency and reasons for retaking cone beam computed tomography (CBCT) scans in an oral and maxillofacial radiology imaging clinic in a dental institution. A retrospective cohort chart audit of the patient image database was performed for 1737 patients attending the Diagnostic Imaging clinic at the Prince Philip Dental Hospital from February 2016 to May 2019, and the rate of, and reasons for, CBCT image re-exposure was tallied. Patient demographics (age and gender) and CBCT acquisition parameters (CBCT unit, field-of-view (FOV), scanned region of interest, and exposure time) were recorded and correlated to retake analysis. The retake rate was 4.6% (80/1737). The most common reasons for re-exposure were incomplete FOV coverage (57.5%) and motion artifacts (27.5%). Patients under 12 years of age had a significantly higher risk for motion artifacts. CBCT for the temporomandibular joint (TMJ) had a significantly higher risk for incomplete FOV coverage. Children (less than 12 years of age) demonstrate a higher frequency of retakes, principally due to motion artifacts. TMJ CBCT examinations have a higher frequency of retakes due to an incomplete FOV coverage. Information regarding the frequency and reasons for CBCT retakes is beneficial to identify procedures, practices, or patients susceptible to additional radiation exposure and implement appropriate and specific quality control protocols.

Recent Advances in Cone-beam CT in Oral Medicine.

The cone-beam computed tomography (CBCT) technology has continuously evolved since its appearance in oral medicine in the early 2000s. To present recent advances in CBCT in oral medicine: i) selection of recent and consensual evidence-based sources, ii) structured summary of the information based on an iterative framework and iii) compliance with ethical, public health and patient-centered concerns. We will focus on technological advances, such as sensors and reconstruction algorithms used to improve the constant quality of the image and dosimetry. CBCT examination is now performed in almost all disciplines of oral medicine: currently, the main clinical disciplines that use CBCT acquisitions are endodontics and oral surgery, with clearly defined indications. Periodontology and ear, nose and throat medicine are more recent fields of application. For a given application and indication, the smallest possible field of view must be used. One of the major challenges in contemporary healthcare is ensuring that technological developments do not take precedence over admitted standards of care. The entire volume should be reviewed in full, with a systematic approach. All findings are noted in the patient's record and explained to the patient, including incidental findings. This presupposes the person reviewing the images is sufficiently trained to interpret such images, inform the patient and organize the clinical pathway, with referrals to other medical or oral medicine specialties as needed. A close collaboration between dentists, medical physicists, radiologists, radiographers and engineers is critical for all aspects of CBCT technology.

Effect of CBCT dose reduction on the mandibular canal visibility: ex vivo comparative study.

To compare the difference in mandibular canal (MC) visibility using three different cone beam computed tomography (CBCT) acquisition protocols: high resolution (HR), standard resolution (ST) and Quick scan+ (QS+). Twenty-five human dry mandibles were scanned by one CBCT machine; i-CAT FLX (Imaging Sciences International, Hatfield, PA, USA), using three different acquisition protocols: high-resolution (HR), standard (ST) and Quick scan+ (QS+). DICOM data were transferred to a third party software Ondemand 3D (Cybermed Co., Seoul, Korea). The fusion module was used to superimpose images derived from different acquisition protocols to standardize the areas to compare the MC visibility. Comparison was performed at nine selected cross sections extending from an area distal to the third molar posteriorly to the first premolar anteriorly. Two expert radiologists evaluated the degree of MC visibility using five-scale scoring system. There was a statistically significant difference between the three acquisition protocols (HR, ST, QS+) at all investigated areas regardless of dentition status (p value < 0.001-0.034) except at the MR1M area where there was no statistically significant difference (p value = 0.094). HR protocol showed the highest prevalence of fully and partially corticated MCat almost all investigated areas while QS+ protocol showed the highest prevalence of invisible MC and clear and unclear non-corticated MC at almost all investigated areas. QS+ protocol of i-CAT FLX CBCT machine is a recommended low-dose CBCT acquisition protocol for MC visibility at dentulous posterior mandibular regions while ST protocol is recommended at edentulous areas.

Triggered Imaging With Auto Beam Hold and Pre-/Posttreatment CBCT During Prostate SABR: Analysis of Time Efficiency, Target Coverage, and Normal Volume Changes

PurposeOur purpose was to investigate time efficiency and target coverage for prostate stereotactic ablative radiation therapy (SABR) using triggered imaging (TI) and auto beam hold. Methods and MaterialsA total of 20 patients were treated with volumetric modulated arc–based SABR. Treatment verification consisted of pre- and post-radiation therapy cone beam computed tomography (CBCT) with gold marker-based TI every 3 seconds. In case of ≥3 mm (deviation limit) displacement, the treatment was interrupted and imaging-based correction was performed. Beam interruptions, intrafractional shifts, and treatment times were recorded. Prostate, rectum, and bladder were delineated on each CBCT. Target coverage was evaluated by comparing the individual prostate delineations with 98% isodose contour volumes (% of the evaluated volumes exceeding the reference). Both inter- and intrafractional changes of bladder and rectal volumes were assessed. ResultsThe average overall treatment time (±standard deviation) was 18 ± 11 min, with a radiation delivery time of 6 ± 3 min if no intrafractional CBCT acquisitions were necessary (91% of fractions). On average, 1.2 beam interruptions per fraction were required with 0/1 correction in 71% of the fractions. The mean residual 3-dimensional shift was 1.6 mm, exceeding the deviation limit in 8%. In the case of intrafractional CBCT and/or ≥2 corrections the treatment time dramatically increased. The 98% isodose lines did not encompass the prostate in only 8/180 (4%) evaluations in 6 different patients, leading to a loss of D98 between 0.1%-6% as a worst case scenario. The bladder volumes showed significant increases during treatment (P < .01) while rectal volumes were stable. ConclusionsTime efficiency of TI + auto beam hold with 3 mm/3 sec threshold during prostate SABR is comparable with competitive techniques, resulting in minimal 3-dimensional residual errors with maintained target coverage. Technical developments are necessary to further reduce radiation delivery time. Use of CBCT allowed full control of rectal volumes, while bladder volumes showed significant increases over time.

3D Assessment of Endodontic Lesions with a Low-Dose CBCT Protocol.

Background: Cone beam computed tomography (CBCT) is often used in different fields of dental science, especially in complex anatomical districts like the endodontic one. The aim of this study is to propose a low-dose CBCT protocol useful in cases of endodontic lesions. Methods: The device used was a MyRay Hyperion X9-11x5; the low dose setting of the machine was 90 Kv, 27 mAs, CTDI/Vol 2.89 mGy. The absorbed organ doses have been evaluated with an anthropomorphic phantom loaded with thermoluminescent dosimeters positioned at the level of sensitive organs like brain, bone marrow, salivary glands, thyroid, esophagus, oral mucosa, extrathoracic airways, and lymph nodes. Equivalent and effective doses have been calculated; the last one has been calculated using the recommendations approved by the Main Commission of ICRP (International Commission Radiological Protection) in March 2007. For the assessment of image quality, five senior clinicians, independent and experienced clinicians, were asked to state if CBCT scans were accurate enough to assess endodontic lesions. Results: The use of a low-dose CBCT acquisition produced the lowest organ dose (5.01 microSv) at the level of the esophagus. Image quality has been considered accurate enough for endodontic diagnostic needs. Conclusions: CBCT low-dose protocol can be used over the standard one in endodontic special cases because it provides a significantly lower radiation dose to the patients while ensuring good image quality. However, further studies are necessary to evaluate the opportunity of low-dose CBCT exams in endodontic clinical practice.

Dosimetric Feasibility of Cone-Beam CT in Pediatric Image-Guided Retrograde Gastrostomy Tube Insertions.

Cone-beam computed tomography (CBCT) in interventional radiology allows volumetric imaging with open patient access. This work aimed to assess radiation dose metrics of CBCT in simulated image-guided retrograde gastrostomy (IGRG) tube insertions in pediatric anthropomorphic phantoms and to compare them to measured radiation dose metrics obtained using fluoroscopy during clinical IGRG tube insertions in children. Radiation dose indices obtained from radiation dose structured reports of fluoroscopic IGRG tube insertions were retrospectively evaluated in a consecutive cohort of 30 children. Dose indices were fractionated into 3 clinical stages for each procedure (planning, insertion, and confirmation). These 3 stages in 30 patients (3 × 30 = 90 patient stages) were compared to dose indices measured from 4 CBCT acquisition protocols acquired in pediatric phantoms. The mean proportion of radiation dose during planning, insertion, and confirmation was 35%, 38% and 27%, with mean reference-point air kerma (range) measured to be 1.0 (0.02-6.0) mGy, 0.9 (0.03-4.1) mGy, and 0.7 (0.04-3.7) mGy, respectively. Cone-beam computed tomography dose varied greatly depending on technical parameters and protocol selection, ranging from 0.7 to 39.3 mGy. In 19% of patient stages, the most dose-sparing CBCT protocol evaluated on phantoms delivered less radiation than the radiation dose indices recorded from patient's fluoroscopy. From a dosimetric perspective, radiation delivered in CBCT can vary widely, yet can be appreciably low. With appropriate CBCT protocol selection, the radiation dose delivered may be sufficiently low to warrant consideration for use, if clinically needed during difficult IGRG tube insertions, and satisfy the interventionalist's benefit-risk assessment.

Head motion during cone-beam computed tomography: Analysis of frequency and influence on image quality.

PurposeImage artifacts caused by patient motion cause problems in cone-beam computed tomography (CBCT) because they lead to distortion of the 3-dimensional reconstruction. This prospective study was performed to quantify patient movement during CBCT acquisition and its influence on image quality.Materials and MethodsIn total, 412 patients receiving CBCT imaging were equipped with a wireless head sensor system that detected inertial, gyroscopic, and magnetometric movements with 6 dimensions of freedom. The type and amplitude of movements during CBCT acquisition were evaluated and image quality was rated in 7 different anatomical regions of interest. For continuous variables, significance was calculated using the Student t-test. A linear regression model was applied to identify associations of the type and extent of motion with image quality scores. Kappa statistics were used to assess intra- and inter-rater agreement. Chi-square testing was used to analyze the impact of age and sex on head movement.ResultsAll CBCT images were acquired in a 10-month period. In 24% of the investigations, movement was recorded (acceleration: >0.10 [m/s2]; angular velocity: >0.018 [°/s]). In all examined regions of interest, head motion during CBCT acquisition resulted in significant impairment of image quality (P<0.001). Movement in the horizontal and vertical axes was most relevant for image quality (R2>0.7).ConclusionRelevant head motions during CBCT imaging were frequently detected, leading to image quality loss and potentially impairing diagnosis and therapy planning. The presented data illustrate the need for digital correction algorithms and hardware to minimize motion artefacts in CBCT imaging.

Augmented Reality Surgical Navigation in Spine Surgery to Minimize Staff Radiation Exposure.

Prospective observational study. To assess staff and patient radiation exposure during augmented reality surgical navigation in spine surgery. Surgical navigation in combination with intraoperative three-dimensional imaging has been shown to significantly increase the clinical accuracy of pedicle screw placement. Although this technique may increase the total radiation exposure compared with fluoroscopy, the occupational exposure can be minimized, as navigation is radiation free and staff can be positioned behind protective shielding during three-dimensional imaging. The patient radiation exposure during treatment and verification of pedicle screw positions can also be reduced. Twenty patients undergoing spine surgery with pedicle screw placement were included in the study. The staff radiation exposure was measured using real-time active personnel dosimeters and was further compared with measurements using a reference dosimeter attached to the C-arm (i.e., a worst-case staff exposure situation). The patient radiation exposures were recorded, and effective doses (ED) were determined. The average staff exposure per procedure was 0.21 ± 0.06 μSv. The average staff-to-reference dose ratio per procedure was 0.05% and decreased to less than 0.01% after a few procedures had been performed. The average patient ED was 15.8 ± 1.8 mSv which mainly correlated with the number of vertebrae treated and the number of cone-beam computed tomography acquisitions performed. A low-dose protocol used for the final 10 procedures yielded a 32% ED reduction per spinal level treated. This study demonstrated significantly lower occupational doses compared with values reported in the literature. Real-time active personnel dosimeters contributed to a fast optimization and adoption of protective measures throughout the study. Even though our data include both cone-beam computed tomography for navigation planning and intraoperative screw placement verification, we find low patient radiation exposure levels compared with published data. 3.