Cone Beam Computed Tomography In Patients Research Articles

A study on the radiomic correlation between CBCT and pCT scans based on modified 3D-RUnet image segmentation.

The present study is based on evidence indicating a potential correlation between cone-beam CT (CBCT) measurements of tumor size, shape, and the stage of locally advanced rectal cancer. To further investigate this relationship, the study quantitatively assesses the correlation between positioning CT (pCT) and CBCT in the radiomics features of these cancers, and examines their potential for substitution. In this study, 103 patients diagnosed with locally advanced rectal cancer and undergoing neoadjuvant chemoradiotherapy were selected as participants. Their CBCT and pCT images were used to divide the participants into two groups: a training set and a validation set, with a 7:3 ratio. An improved conventional 3D-RUNet (CLA-UNet) deep learning model was trained on the training set data and then applied to the validation set. The DSC, HD95 and ASSD were calculated for quantitative evaluation purposes. Then, radiomics features were extracted from 30 patients of the test set. The experiments demonstrate that, the modified model achieves an average DSC score 0.792 for pCT and 0.672 for CBCT scans. 1037 features were extracted from each patient's CBCT and pCT images, 73 image features were found to have R values greater than 0.9, including three features related to the staging and prognosis of rectal cancer. In this study, we proposed an automatic, fast, and consistent method for rectal cancer GTV segmentation for pCT and CBCT scans. The findings of radiomic results indicate that CBCT images have significant research value in the field of radiomics.

A Pilot Study of Simulation-Free Hippocampal-Avoidance Whole Brain Radiotherapy Using Diagnostic MR-Based and Online Adaptive Planning

We aimed to demonstrate the clinical feasibility and safety of a simulation-free hippocampal avoidance whole brain radiotherapy (HA-WBRT) workflow in a Phase I clinical trial (NCT05096286). Feasibility was defined as successful completion of the simulation-free HA-WBRT workflow through treatment delivery in at last 70% of treated patients. Ten candidates for HA-WBRT were enrolled for treatment on a ring gantry CT-guided Linac with online adaptive capabilities. Structures were contoured on the diagnostic brain MRI, which was then registered to a separate head computed tomography (CT) of similar head shape, obtained from an atlas-based database. A HA-WBRT "pre-plan" was generated using the atlas-based CT (AB-CT) and the NRG-CC001 constraints. At first fraction, the AB-CT was used as the primary dataset and deformed to the patient's cone-beam CT (CBCT) for dose calculation. The brain, ventricles, and brainstem contours were matched through rigid translation and rotation to the corresponding anatomy on the CBCT to aid in alignment, given the differences in rotational head positioning from diagnostic MRI to CBCT setup. Lastly, the lens, optic nerves, and brain contours were manually edited based on CBCT visualization. Plans were then optimized, and the adaptive plan was chosen for treatment if the plan met all objectives. Workflow tasks were timed. In addition, conventional plans using patients' sim CTs were created for each patient for the purpose of prospective dosimetric comparison. The dosimetric parameters were compared for each patient between the delivered sim-free plan and the conventional sim CT plan using the sign test via statistical software, with p<.05 indicating significance. Median time from approved sim order to first fraction was 4 days (range: 2-7); median time in room (door-to-door) was 49 minutes (range: 35-70). All patients successfully completed all ten fractions and 90% of the simulation-free radiation plans met all NRG-CC001 constraints. For one patient, the sim-free plan at fraction one failed the planning target volume (PTV) coverage objective (coverage of 89%); this was deemed acceptable for delivery by the treating radiation oncologist. An offline replan was then performed to meet NRG-CC001 constraints and used for the subsequent nine fractions. There was no clinically meaningful difference in dosimetric constraints between the sim-free plan (calculated on AB-CT) and conventional CT sim plan. Statistically, the sim-free plans provided improved PTV coverage to higher doses compared to the conventional plans (Table). At a median follow-up of 43 days (range: 9 -280), the intracranial progression-free survival rate was 90%. Simulation-free HA-WBRT is feasible, results in plans that are dosimetrically comparable to conventional CT sim workflows and succeeds in decreasing time to initiation of HA-WBRT by at least 50%. Further studies with a larger cohort are warranted to optimize the workflow.

Stress Trajectory Variations During Occlusal Loading in Human Skull with a Maxillofacial Defect: A Finite Element Analysis.

Biting forces from the teeth are distributed to the facial bones and to the skull through the stress trajectories. The presence of a bony defect in either the maxilla or mandible might lead to variations in the stress distribution. The aim of this study was to evaluate the stress distribution and variations in stress trajectories from biting forces in a human skull with maxillofacial defect using a finite element (FE) model. In this study, a cone beam computed tomography (CBCT) of an adult male patient with a maxillectomy defect consequent to surgical treatment of mucormycosis is evaluated for the stress distribution from the biting forces of the remaining posterior teeth. Finite element model without the mandible was constructed from the patient's CBCT data. Occlusal loading forces of 600N were applied on each side of the maxillary teeth. Stress trajectories were visualised through the stress distribution pattern. The results showed deviations in the normal stress distribution during occlusal loading and variations in zygomatic and pterygoid stress trajectories in the maxillofacial and skull regions in our FE model due to the bony defect. We conclude that a skeletal maxillofacial defect should be reconstructed to resume proper stress distribution during functional forces to maintain a healthy craniofacial skeleton.

Evaluation of Two Computerized Methods for Presurgical Volumetric Analysis in Secondary Alveolar Cleft Bone Grafting: A Prospective Study

The purpose of this study is to evaluate presurgical computerized volumetric analysis in secondary alveolar cleft bone grafting (SABG) and the time taken for calculation using cone-beam computed tomography (CBCT) via two different software programs. Twelve patients with unilateral alveolar clefts were investigated using CBCT. Two independent investigators did presurgical volumetric analysis for each patient's CBCT data using two different methods. Method A involved On-Demand 3D software (Cybermed Inc., Korea), while method B involved InVesalius 3 software (CTI, Brazil). The volume outcomes and time spent for measurements were compared between both software programs. Interobserver reliability and descriptive and t-test statistics were computed, and statistical significance was considered when p ≤ 0.05. There was not a statistically significant difference between clefts' volumetric measurements by the two methods via both investigators (p = 0.186 and 0.069). However, the difference in time taken for these measurements between the two methods was statistically significant (p < 0.001). Intraclass correlation coefficient (ICC) values indicated excellent interobserver reliability for measurements by method A (ICC ~ 0.998), and moderate reliability for method B (ICC ~ 0.626). Both software programs used in this study had comparable volumetric computation. Method B took much less calculating time than method A. The interobserver reliability was high for both methods. These both investigated software programs may show a clinical implication for presurgical alveolar cleft volume measurement, thus reducing the surgical operating time and adequately selecting a donor site with a congruent sufficient amount of bone grafts.

Dosimetric Analysis of Online Adaptive Radiation Therapy in the Adjuvant Setting for Head and Neck Cancer

<h3>Purpose/Objective(s)</h3> Online adaptive radiotherapy (OnART) system designed to deliver re-optimized plans in real time using on-board cone beam CT and artificial intelligence has enabled frequent adaptation. Given the paucity of data on the role of adaptive radiotherapy (RT) and its frequency in the treatment of post-operative patients with head and neck squamous cell carcinoma (HNSCC), a dosimetric study was performed to assess the potential benefits of a single vs weekly OnART in this setting. <h3>Materials/Methods</h3> Twelve patients receiving conventionally fractionated RT (CFRT) over 6 weeks and 12 patients receiving hypofractionated RT (HFRT) over 3 weeks on a clinical trial between 2020 and 2021 were analyzed. The OnART plan was generated to meet the same quality as the original clinical plan and the OnART emulator was used to virtually conduct adaptive RT based on the patient's cone beam CT. The PTV coverage, dose heterogeneity, and cumulative dose to the organs-at-risk of a single mid-treatment OnART (at week 4 for CFRT and week 2 for HFRT) and weekly OnART were compared to the non-adapted plan. <h3>Results</h3> In total, 13, 8, and 3 patients had oral cavity, oropharynx, and larynx primaries, respectively, with 11 of the 24 patients receiving ipsilateral RT only. The average absolute and % weight loss during treatment were 5.7 lb and 3.1%, respectively. In the CFRT cohort, weekly OnART led to a significant improvement in high risk PTV (PTVHR) and standard risk PTV (PTVSR) V100 coverage (9.9% and 3.4% absolute) as well as hot spot (-1.3 Gy), max cord dose (-3.4 Gy), and mean oral cavity dose (-1.3 Gy), while the mean contralateral parotid dose increased modestly (0.76 Gy) (Table). When adapted once, only PTVHR coverage was improved (3.3%). For the HFRT cohort, weekly OnART resulted in a significant improvement in PTVHR/PTVSR coverage (3.7%/2.0%), hot spot (-0.82 Gy), and max cord dose (-2.5 Gy) (Table). When adapted once, mean oral cavity dose decreased (-1.4 Gy) and mean contralateral parotid dose increased (1.1 Gy). <h3>Conclusion</h3> There was a limited benefit of one-time OnART, but weekly adaptations improved the dosimetry, predominantly in PTV coverage and dose heterogeneity for patients receiving adjuvant RT for HNSCC. A prospective study is ongoing to determine the potential benefit in clinical and patient-reported outcomes of OnART in this setting.

A Novel Simplified Workflow for Guided Endodontic Surgery in Mandibular Molars With a Thick Buccal Bone Plate: A Case Report

One of the challenges in apical surgery in mandibular molars is the thick buccal cortical bone plate, which might lead to access errors, damage to neighboring teeth, and injury to healthy tissue. Surgical guide templates with 3-dimensional (3D) impressions have been suggested for use in such cases, allowing greater precision. Usually, this technique involves a cone-beam computed tomography (CBCT) examination related to a 3D oral scanning to generate surgical templates printed from 3D imaging data. This study reports a novel workflow possibility in which apical surgery is performed with the aid of a surgical guide planned only with CBCT, excluding the need for 3D oral scanning. A 32-year-old woman presented with asymptomatic apical periodontitis and external root resorption on the mesial root of tooth #19. A surgical template was planned using only the patient's CBCT scan to provide precise access to the lesion and remove a mandibular cortical bone block. The procedure was carried out with apicoectomy, root-end preparation, and retrograde filling, and the bone block was repositioned before suture. No postoperative complications were reported. After 1 year, the patient presented asymptomatic, and a CBCT scan confirmed bone healing. The current 3D-printed guides may be planned and printed through a novel simplified workflow with a CBCT scan only, which allows its application in apical surgery for precise apex and surgical site location.

Evaluation of bone density by cone-beam computed tomography and its relationship with primary stability of dental implants

One of the critical factors determining the success of dental implants is primary stability. This study aimed to determine the density of jawbones in the implant candidate sites via cone-beam computed tomography (CBCT) and its correlation with the values obtained from resonance frequency analysis during surgery. In this descriptive-analytic study seventeen implant sites requiring implant placement were selected. Impressions were sent to the laboratory to construct a surgical guide via the stereolithographic method. An electronic surgery was performed on the chosen implant sites according to each patient's CBCT information entered into the Kaveh surgical guide software. The bone density of the target areas was calculated using the gray value (voxel value). After preparing the final osteotomy, an implant was installed in the area according to the manufacture's recommendation. The relevant Osstell® SmartPeg was selected and installed on the implant body to determine the primary stability. Kolmogorov-Smirnov test and the correlation pearson correlation statistical test. used for statistical analyze. P value amounts < 0.05 was considered significant. The mean and standard deviation of the gray scale in this study were 563.7 ± 218.8 and 65.3 ± 7.7 implant stability quotient (ISQ) respectively. The correlation between gray scale and ISQ was evaluated by the Pearson correlation test, and the results indicated a strong correlation between the two variables. The voxel value and primary stability had a normal distribution and strong correlation. In other words, the gray scale determined by CBCT imaging techniques at the proposed implant site could be used to assess the bone density before the surgery.

Evaluation of the accuracy of cone beam computed tomography (CBCT) generated tooth replicas with application in autotransplantation

ObjectivesThe primary aim of this study was to assess the linear and geometric accuracy of 3-dimensional (3D) printed tooth replicas when compared to the actual tooth. The secondary aims were to compare the accuracy of three different 3D printers and to evaluate dimensional changes of tooth replicas after sterilization. MethodsA sample of 16 teeth were selected from recruited patients. Segmentation was carried out to generate files from the patient's cone beam computed tomography (CBCT) data, Tooth replicas were then printed using three printers making use of Polyjet, laser stereolithography (SLA) and digital light processing (DLP) technology respectively. These replicas, along with the actual tooth, were scanned by an optical scanner. Replicas were sent for sterilization and scanned again. Paired superimposition of the scans was performed. ResultsA mean length difference of 0.36 mm and mean geometric (root mean square [RMS]) difference of 0.56 mm was found. Qualitative analysis showed that the replicas were generally larger in size. Repeated ANOVA tests showed that the Polyjet printer had the highest accuracy (p<0.0001). After sterilization, there was an overall mean length difference of 0.10 mm and RMS deviation of 0.02 mm. ConclusionThis study found that there was a significant difference in linear and geometric measurements of the tooth replicas when compared to the actual tooth. This study also provides evidence that the printer which made use of Polyjet technology was able to produce more accurate models than SLA or DLP printers. Printed tooth models demonstrated clinically insignificant changes after heat sterilization. Clinical significance3D printed tooth replicas derived from the patient's CBCT data may be used in autotransplantation to increase predictability of the procedure. In order for this novel digital approach to realize its potential, it is critical to address questions as to how accurate the various printing technologies are in fabricating replicas.

Cone-beam CT versus Multidetector CT in Postoperative Cochlear Implant Imaging: Evaluation of Image Quality and Radiation Dose.

Cone-beam CT is being increasingly used in head and neck imaging. We compared cone-beam CT with multidetector CT to assess postoperative implant placement and delineate finer anatomic structures, image quality, and radiation dose used. This retrospective multicenter study included 51 patients with cochlear implants and postoperative imaging via temporal bone cone-beam CT (n = 32 ears) or multidetector CT (n = 19 ears) between 2012 and 2017. We evaluated the visualization quality of single electrode contacts, the scalar position of the electrodes, cochlear walls, mastoid facial canal, metallic artifacts (using a 4-level visual score), and the ability to measure the insertion angle of the electrodes. The signal-to-noise ratio and radiation dose were also evaluated. Cone-beam CT was more sensitive for visualizing the scalar position of the electrodes (P = .046), cochlear outer wall (P = .001), single electrode contacts (P < .001), and osseous spiral lamina (P = .004) and had fewer metallic artifacts (P < .001). However, there were no significant differences between both methods in visualization of the modiolus (P = .37), cochlear inner wall (P > .99), and mastoid facial canal wall (P = .07) and the ability to measure the insertion angle of the electrodes (P > .99). The conebeam CT group had significantly lower dose-length product (P < .001), but multidetector CT showed a higher signal-to-noise ratio in both bone and air (P = .22 and P = .001). Cone-beam CT in patients with cochlear implants provides images with higher spatial resolution and fewer metallic artifacts than multidetector CT at a relatively lower radiation dose.

Intratympanic application of triamcinolone in sudden hearing loss\u2014radiologic anatomy in cone beam CT and its\u2019 correlation to clinical outcome

PurposeTo evaluate temporal bone cone-beam CT in patients with idiopathic sudden sensorineural hearing loss (ISSNHL) being treated with primary and secondary intratympanic (IT) triamcinolone and to possibly correlate these results to the clinical outcome.MethodsRetrospective analysis of patients treated with IT triamcinolone for ISSNHL at our department in 2018. Pre- and post-therapeutic audiologic examinations included four-tone average (FTA) at 0.5, 1, 2 and 3 kHz. Using a clinical questionnaire, pre-therapeutic CBCT scans were re-evaluated looking at items, which might interfere with adequate drug diffusion into the inner ear (e.g. bony overhangs or secondary membranes at the round or oval window).ResultsThirty-one patients were included. Twenty-four (77%; group A) had experienced ineffective systemic steroid therapy before and seven (23%; group B) received primary IT injections. Four group A-patients (21%) and two group B-patients (33%) showed a post-therapeutic FTA improvement of more than 15 dB HL. Bony overhangs at the round window niche (RWN) were present in seven cases (26%), a secondary membrane at the RWN in four (15%) and soft tissue in eight (30%) cases, respectively.ConclusionMost patients present radiological findings in CBCT imaging, which might interfere with drug diffusion through the RW membrane. Interestingly, soft or bony tissue obstructing the RWN or the OWN was found in 50% of patients, who showed improvement of hearing. We conclude that radiologic ‘tiny’ findings are either clinically irrelevant or improvement in hearing is independent from intratympanic drug delivery.

Identification of Specific Panoramic High-Risk Signs in Impacted Third Molar Cases in Which Cone Beam Computed Tomography Changes the Treatment Decision

The aim of this study was to investigate the treatment decisions of oral-maxillofacial surgeons in the management of impacted lower third molars (M3s) according to panoramic radiography (PR) and cone beam computed tomography (CBCT) risk analysis. Ten surgeons analyzed 40 deliberately selected M3 cases showing 1 or more panoramic high-risk signs: 1) darkening of the root, 2) interruption of the white line, 3) diversion of the inferior alveolar canal (IAC), 4) narrowing of the IAC, and 5) 2 or more signs occurring simultaneously (including darkening and/or interruption of the IAC). After evaluating the PR images, the observers analyzed the patients' CBCT images. The treatment decision (extraction vs coronectomy) and surgical technique (number of planned tooth sections) were recorded. On the CBCT coronal slices, direct contact between the M3 and IAC, together with narrowing and/or fenestration of the IAC, was observed most frequently when 2 or more panoramic signs were seen simultaneously on the PR images (odds ratio [OR], 7.2; P=.021). CBCT findings led to a significant decrease in the number of coronectomy decisions (23% vs 14.5%, P=.002), which was most prominent in the groups showing panoramic signs of darkening (approximately 50%, P=.007) and narrowing (approximately 66%, P=.044). A significant number of extraction decisions were modified to coronectomy when 2 or more panoramic signs occurred together (OR, 7.9; P<.001). However, there were no significant differences regarding the number of planned hypothetical tooth sections. The results showed that the surgeons' confidence in the treatment decision increased after CBCT imaging, resulting in fewer coronectomy decisions. CBCT information that changed a previous coronectomy decision to extraction was most frequently observed in cases showing darkening and narrowing PR signs. The chance of changing an extraction decision to a coronectomy decision after evaluating the patient's CBCT images was the highest when 2 or more PR signs were observed simultaneously.

Comparison of ultimate force revealed by compression tests on extracted first premolars and FEA with a true scale 3D multi-component tooth model based on a CBCT dataset.

The aim of this study was to develop a new method for creating a multi-component and true scale 3-dimensional (3D) model of a human tooth based on cone-beam computed tomography (CBCT) images. First maxillary premolar tooth model was reconstructed from a patient's CBCT images. The 2D serial sections were used to create the 3D model. This model was used for finite element analysis (FEA). Model validation was performed by comparing the ultimate compressive force (UF) obtained experimentally using a universal testing machine and from simulation. The simulations of three component-omitting models (silicone, cementum, and omitting both) were performed to analyze the maximum (max.) principal stress and stress distribution. The simulation-based UF indicating tooth fracture was 637N, while the average UF in the in vitro loading was 651N. The discrepancy between the simulation-based UF and the experimental UF was 2.2%. From the simulation, the silicone-omitting models showed a significant change in max. principal stress, resulting in a UF error of 26%, whereas there was no notable change in the cementum-omitting model. This study, for the first time, developed a true scale multi-component 3D model from CBCT for predicting stress distribution in a human tooth. This study proposed a method to create 3D modeling from CBCT in a true scale and multi-component manner. The PDL-like component-omitting simulation led to a higher error value of UF, indicating the importance of multi-component tooth modeling in FEA. Tooth 3D modeling could help determine mechanical failure in dental treatments in a more precise manner.

Efficacy and safety of transarterial chemoembolisation with cone-beam CT in patients with hepatocellular carcinoma within the Milan criteria: a retrospective cohort study

To compare the therapeutic efficacy and safety of transarterial chemoembolisation (TACE) for hepatocellular carcinoma (HCC) within the Milan criteria with or without the use of cone-beam computed tomography (CBCT). Patients with HCC within the Milan criteria who underwent conventional angiography-guided TACE (Angio-TACE group: 58 patients from January 2010 to December 2011) were compared with those who underwent CBCT-guided TACE (CBCT-TACE group: 55 patients from January 2013 to December 2014). Local progression-free survival (LPFS), progression-free survival (PFS), and overall survival (OS) were compared. Adverse events after TACE were also investigated. Baseline characteristics were balanced between the two groups. LPFS was significantly longer in the CBCT-TACE group than in the Angio-TACE group (median: not reached for 36 versus 19.2 months, respectively; Log-rank p=0.029). In multivariable Cox regression analysis, CBCT guidance had a significantly lower risk of local progression or death (adjusted hazard ratio: 0.585; 95% confidence interval, 0.344-0.995; p=0.048); however, there was no significant difference in PFS (3-year PFS: 15.9% versus 26.8%, respectively; p=0.122) or OS (3-year OS: 85% versus 88.2%, respectively; p=0.761) between the Angio-TACE and CBCT-TACE groups. Post-embolisation syndrome occurred significantly less frequently in the CBCT-TACE group (p=0.002). CBCT-guided TACE could improve local tumour control for HCC within Milan criteria and showed fewer cases of post-embolisation syndrome.

On-Board Cone Beam Computed Tomography as Radiation Therapy Simulation for Emergent Cases

To investigate dosimetric clinical appropriateness of on-board kV cone beam computed tomography patient simulation (CBCT-Sim) for palliative treatment plans at a remote satellite clinic having no conventional computed tomographic simulation (CT-Sim) when travel isn't a viable option. Our current approach is a separation calculation using two opposing fields on a water phantom. A CBCT of the patient would improve the plan by utilizing the patient's actual geometry and we expect to see dose points in the CBCT-Sim plan image set less than 3% different than a conventional CT, and the separation calculation to be within 5% of the conventional CT-Sim plan. Patients treated for the four most likely emergent or immobile disease sites (brain, thoracic spine, lumbar spine, and pelvis) with an original CT-Sim and at least one CBCT during course of treatment were investigated retrospectively. Three brain patients, three T-spine, three L-spine, and two pelvis patients were used. The patients’ images were copied into a new, anonymous patient. A new CT-density curve was created in the treatment planning software for the CBCT based on CT-density phantom data. A standard plan for each given site was planned on the original CT image set, then copied on both a heterogenous and homogenous CBCT image set. The homogenous CBCT image was density overridden to water. A rectangular water phantom was also created for a separation calculation plan, which is our standard practice for these cases. For the brain cases, the CT and heterogenous CBCT plans were both contoured with critical structures. For all cases, seven to eleven points of interest in all directions (isocenter, and fractional separation distances in 3-dimentional space) were used to compare both CBCT-Sim plans and the separation calculation to the standard CT plan. For all cases, the average dose difference per case compared to the standard CT-Sim plan was less than 3% for either CBCT-Sim plan and less than 4% for the separation calculation plan; however, the separation calculations showed large deviations, up to 7.2%, while the CBCTs showed a maximum of 4.8%. Between all cases, the average dose difference was lowest compared to CT-Sim plans for the heterogenous CBCT plan with 1.2±0.7%, while the homogenous CBCT plan difference was 1.4±0.7% and the separation calculation was 1.7±1.1%. The most dosimetric benefit for the heterogenous CBCT-Sim plans was seen for the brain plans, followed by the T-spine plans, with negligible benefit for pelvis and L-spine plans. Dosimetric accuracy is improved with a CBCT-Sim compared to our standard separation-based plan, due to the use of actual patient geometry and density.

P234] Waiting and treatment time analysis for radiation therapy treatments

Purpose To analyze the total treatment time and waiting time for the patients in our radiation oncology department. Method Patient treatment and waiting times were analyzed for a total of 3937 appointments during the last 3 years in three linear accelerators (Agility, Synergy and Infinity). With Elekta’s MOSAIQ Radiation Oncology information system (version 2.60, IMPAC Medical Systems), all patient information is collected and accessible, so you can create exhaustive reports. For this study a report including arrival time, wait time, treatment time and total time in the department was created for all radiotherapy treatments. Agility and Synergy are located in the same site, but Infinity is in a satellite location. Agility machine is dedicated mostly to VMAT treatments, meanwhile Synergy carry on only 3D treatments and Infinity performs VMAT as well as 3D treatments. Results Medium total treatment time was 15.1 min; median was 13.9 min. On average, patients arrive 30.5 min before the scheduled time. Therefore mean total time in the department was 45.6 min. In addition, for each machine, results were as follow: Agility: 1214 appointments. Average (minutes): early arrival 44.7, total time 45.3, wait time 30.6 and treatment time 14.8. Only 9.6% of the appointments arrived late. Synergy: 1541 appointments. Average (minutes): early arrival 36.8, total time 45.5, wait time 29.8 and treatment time 15.7. A 9.4% of the appointments arrived late. Infinity: 1182 appointments. Average (minutes): early arrival 22.0, total time 46.1, wait time 31.3 and treatment time 14.8. A 21.9% of the appointments arrived late. Conclusions In summary, patient waiting time and total time are very similar for the three machines. Despite the fact all VMAT treatments have a daily cone beam CT for patient positioning; medium treatment time for Agility is similar to the other machines which perform less VMAT treatments. Furthermore, many patients depend on public/private transport to arrive to their appointments; Infinity machine has the higher rate of late appointments, which could be related with a problem in the transport system. Therefore these results not only provide feedback but also could allow detecting problems and consequently improving waiting times for the patients.

A Picture is Not Worth a Thousand Words – Implementation of Offline Volumetric Image Review

The current institutional practice of communicating Head and Neck patient set-up problems and issues identified during image-guided radiation therapy (IGRT) is through email to the responsible radiation oncologist (RO). The email includes a screen capture of a single cone-beam computed tomography (CBCT) slice with a written description of the problem identified by front-line Radiation Therapists (RTTs). To gain a better understanding of the issue, the RO will often attend patient set-up the next day to review the CBCT with the RTTs on the treatment unit. To eliminate decision-making based on a single screen shot of a volumetric image and to reduce the number of times ROs are required at the treatment unit for online review, the use of Image Review Workspace in the Radiation Therapy Electronic Medical Records (RTEMR) system was piloted. The process for offline CBCT image review in Image Review Workspace within RT EMR was tested for feasibility through collaboration with the Head and Neck site leads (RO, Medical Physics [MP], RTT) and the clinical application specialist team. Workflow for offline review was assessed for feasibility and ease of use; technical issues identified were resolved prior to pilot roll-out. The workflow for offline review in Image Review Workspace initiates with an email alert by front line RTTs to the responsible RO, planner, and MP outlining the issue identified on the daily CBCT, requesting for image review. The RO would then view the volumetric CBCT in RTEMR and provide feedback regarding the set-up issue before the next clinical day. The image in RTEMR would not require approvals as the workspace is used solely as a platform to view the issue volumetrically. To assist with pilot implementation, training documents and teaching sessions were prepared for front-line RTTs and Head and Neck ROs describing the tools available within Image Review Workspace to view the patient CBCTs. Additionally, a standardized email template was created to ensure staff were comprehensive when describing IGRT issues, including a link with the instructions for using Image Review Workspace. The benefit of using the Image Review Workspace in RTEMR is that ROs can view the patient's entire CBCT image in a volume versus a single slice; decision-making is more informed based on three-dimensional data. This process also reduces the number of times ROs are required to attend set-up at the treatment unit to investigate image guidance issues. One identified challenge of Image Review Workspace is the amount of time required to initially load the patient's CBCT image, which can take up to two minutes. The ability to review CBCTs offline in a volumetric environment aids in clinical decision making and communication between the ROs and front-line team. Through the success of this pilot on the Head and Neck site, the process for offline CBCT image review in RTEMR is being implemented by other sites at our institution.

Computer-aided cephalometric landmark annotation for CBCT data.

Nowadays, with the increased diffusion of Cone Beam Computerized Tomography (CBCT) scanners in dental and maxillo-facial practice, 3D cephalometric analysis is emerging. Maxillofacial surgeons and dentists make wide use of cephalometric analysis in diagnosis, surgery and treatment planning. Accuracy and repeatability of the manual approach, the most common approach in clinical practice, are limited by intra- and inter-subject variability in landmark identification. So, we propose a computer-aided landmark annotation approach that estimates the three-dimensional (3D) positions of 21 selected landmarks. The procedure involves an adaptive cluster-based segmentation of bone tissues followed by an intensity-based registration of an annotated reference volume onto a patient Cone Beam CT (CBCT) head volume. The outcomes of the annotation process are presented to the clinician as a 3D surface of the patient skull with the estimate landmark displayed on it. Moreover, each landmark is centered into a spherical confidence region that can help the clinician in a subsequent manual refinement of the annotation. The algorithm was validated onto 18 CBCT images. Automatic segmentation shows a high accuracy level with no significant difference between automatically and manually determined threshold values. The overall median value of the localization error was equal to 1.99 mm with an interquartile range (IQR) of 1.22-2.89 mm. The obtained results are promising, segmentation was proved to be very robust and the achieved accuracy level in landmark annotation was acceptable for most of landmarks and comparable with other available methods.

SU‐C‐207‐05: A Comparative Study of Noise‐Reduction Algorithms for Low‐Dose Cone‐Beam Computed Tomography

Purpose:To study different noise‐reduction algorithms and to improve the image quality of low dose cone beam CT for patient positioning in radiation therapy.Methods:In low‐dose cone‐beam CT, the reconstructed image is contaminated with excessive quantum noise. In this study, three well‐developed noise reduction algorithms namely, a) penalized weighted least square (PWLS) method, b) split‐Bregman total variation (TV) method, and c) compressed sensing (CS) method were studied and applied to the images of a computer–simulated “Shepp‐Logan” phantom and a physical CATPHAN phantom. Up to 20% additive Gaussian noise was added to the Shepp‐Logan phantom. The CATPHAN phantom was scanned by a Varian OBI system with 100 kVp, 4 ms and 20 mA. For comparing the performance of these algorithms, peak signal‐to‐noise ratio (PSNR) of the denoised images was computed.Results:The algorithms were shown to have the potential in reducing the noise level for low‐dose CBCT images. For Shepp‐Logan phantom, an improvement of PSNR of 2 dB, 3.1 dB and 4 dB was observed using PWLS, TV and CS respectively, while for CATPHAN, the improvement was 1.2 dB, 1.8 dB and 2.1 dB, respectively.Conclusion:Penalized weighted least square, total variation and compressed sensing methods were studied and compared for reducing the noise on a simulated phantom and a physical phantom scanned by low‐dose CBCT. The techniques have shown promising results for noise reduction in terms of PSNR improvement. However, reducing the noise without compromising the smoothness and resolution of the image needs more extensive research.

Dacryocystography using cone beam CT in patients with lacrimal drainage system obstruction.

To assess the usefulness of cone beam CT (CBCT) for dacryocystography (DCG) using either direct syringing or passive application of contrast medium. Ten consecutive patients with epiphora who had CBCT-DCG in a sitting position were retrospectively analyzed. CBCT-DCGs were performed using 2 techniques: direct syringing with contrast medium or using the passive technique, where patients received 3 drops of contrast medium into the conjunctival sac before CBCT-DCG. Clinical and radiologic diagnoses were compared for both groups. The 10 patients (men = 3) had a mean age of 63.2 years. Both techniques proved to be simple procedures with good delineation of the bone, soft tissue, and the contrast medium in the lacrimal system. No side effects were noted. CBCT-DCG is a useful alternative to determine the localization of stenosis in patients with chronic epiphora.

SU‐F‐18C‐15: Model‐Based Multiscale Noise Reduction On Low Dose Cone Beam Projection

Purpose:To improve image quality of low dose cone beam CT for patient positioning in radiation therapy.Methods:In low dose cone beam CT (CBCT) imaging systems, Poisson process governs the randomness of photon fluence at x‐ray source and the detector because of the independent binomial process of photon absorption in medium. On a CBCT projection, the variance of fluence consists of the variance of noiseless imaging structure and that of Poisson noise, which is proportional to the mean (noiseless) of the fluence at the detector. This requires multiscale filters to smoothen noise while keeping the structure information of the imaged object. We used a mathematical model of Poisson process to design multiscale filters and established the balance of noise correction and structure blurring. The algorithm was checked with low dose kilo‐voltage CBCT projections acquired from a Varian OBI system.Results:From the investigation of low dose CBCT of a Catphan phantom and patients, it showed that our model‐based multiscale technique could efficiently reduce noise and meanwhile keep the fine structure of the imaged object. After the image processing, the number of visible line pairs in Catphan phantom scanned with 4 ms pulse time was similar to that scanned with 32 ms, and soft tissue structure from simulated 4 ms patient head‐and‐neck images was also comparable with scanned 20 ms ones. Compared with fixed‐scale technique, the image quality from multiscale one was improved.Conclusion:Use of projection‐specific multiscale filters can reach better balance on noise reduction and structure information loss. The image quality of low dose CBCT can be improved by using multiscale filters.