Pretreatment Cone-beam Computed Tomography Research Articles

Clinical Utility of Deformable Image Registration in Early Prediction of Rectal Bleeding Risk in Prostate Cancer Radiotherapy

To evaluate the clinical utility of deformable image registration (DIR) in the early prediction of rectal bleeding in prostate cancer radiotherapy. 240 images (24 plan-CT and 216 pretreatment cone-beam CT (CBCT)) from 24 prostate adenocarcinoma patients were prospectively acquired during the first fifteen fractions of their real treatment (76 Gy in 38 fractions). After correlation with a deformable image registration (DIR), doses of a virtual treatment plan (57.3 Gy in 15 fractions) were mapped from each CBCT to the plan-CT, allowing the identification of patients who have exceeded the dose limitation for 50% of the rectum (R50). We classified patients according to whether or not they had fulfilled the R50 constraint and we compared with student t-test their variation rate (VR) = [100 x (dose delivered to R50 - planned dose to R50 / planned dose to R50)] during the first 5 sessions. Using Roc curves, we also studied if during these first fractions a value of VR could reliably predict the risk of not complying with the constraint and therefore the risk of rectal bleeding. 15 patients would have met the R50 limitation and 9 would not. Significant differences in the VR between both subgroups have been found in fractions 1, 3 and 5 (t = - 3.192, p = 0.008; t = - 5.683, p< 0,001; t = - 5,340, p< 0,001). In fraction 1, a value of VR > 0% would have predicted the risk of rectal overdosage with a sensitivity of 66.7% and a specificity of 73.3%. In fractions 3 and 5, a VR value > 1% would have predicted the risk of rectal overdosage in the same way, with a sensitivity of 100% and a specificity of 93.3%. After a median follow-up of 56.5 months there have been three rectal bleeding cases (with endoscopic confirmation), all of them would have been detected in fraction three with the VR value established as predictive of rectal toxicity. This study demonstrated the clinical utility of DIR in establishing already in fraction 3 a VR value (>1%) that reliably predicts the risk of rectal bleeding, even if we use a different schedule than the one used for its calculation.

Application of 3D tooth model for monitoring of implant space and inter-root distance without radiographs: a proof of concept study

BackgroundRadiographs are integral in evaluating implant space and inter-root distance. The purpose of this report is to introduce a method for evaluating the 3D root position with minimal radiation using a 3D tooth model composed of an intraoral-scanned crown and a cone-beam computed tomography (CBCT)-scanned root.Materials and methodsIntraoral scan and CBCT scan of the patient were obtained before treatment. In the CBCT image, tooth segmentation was performed by isolating individual teeth from the maxillary and mandibular alveolar bone using software program. The 3D tooth model was fabricated by combining segmented individual teeth with the intraoral scan.ResultsA post-treatment intraoral scan was integrated into the tooth model, and the resulting position of the root could be predicted without additional radiographs. It is possible to monitor the root position after a pretreatment CBCT scan using a 3D tooth model without additional radiographs.ConclusionThe application of the 3D tooth model benefits the patient by reducing repeated radiation exposure while providing the clinician with a precise treatment evaluation to monitor tooth movement.

Intra-fraction and Inter-fraction analysis of a dedicated immobilization device for intracranial radiation treatment

BackgroundImmobilization devices are crucial to minimize patient positioning uncertainties in radiotherapy (RT) treatments. Accurate inter and intra-fraction motions is particularly important for intracranial and stereotactic radiation treatment which require high precision in dose delivery. Recently, a new immobilization device has been developed specifically for the radiation treatment of intracranial malignancies. To date, no data are available on the use of this device in daily clinical practice. The aim of this study is to investigate the intra and inter-fraction variations, patient comfort and radiographer confidence of the immobilization system from two distinct institutions: HagaZiekenhuis, Den Haag, Netherlands and IRCCS Ospedale Sacro Cuore Don Calabria, Negrar, Italy.Material and methodSixteen patients (10 diagnosed with brain metastases and 6 with primary central nervous systemic tumor) from IRCCS Ospedale Sacro Cuore Don Calabria and 17 patients (all diagnosed with brain metastases tumor) from HagaZiekenhuis were included in this study. The median target volume was 436 cc (range 3.2–1628 cc) and 4.58 cc (range 0.4–27.19 cc) for IRCCS and Haga, respectively. For patients treated in IRCCS Sacro Cuore Don Calabria, the median dose prescription was 30 Gy (range 27–60 Gy) and median number of fractions 10 (range 3–30). In Haga the median dose prescription was 21 Gy (range 8–21 Gy) and the median number of fraction was 1 (range 1–3). The immobilization device was assembled during CT simulation. A short interview to the patient regarding the device’s comfort level was conducted at the end of the simulation procedure. Additionally, simulation setup time and radiographer (RTT) procedures (i.e. mask preparation) were evaluated. Prior to radiation treatment delivery, an automatic rigid match on the cranial bones between cone beam computed tomography (CBCT) and planning-CT was performed. A couch shift was performed subsequently. An extra post-treatment CBCT was acquire after the treatment delivery. This post-treatment CBCT was matched with pre-treatment CBCT to identify any possible intra-fraction motion. All online matches were validated by experienced radiation oncologist or RTT. A total of 126 CBCT’s were analyzed offline by radiation oncologist/medical physicist. The data of the pre-treatment CBCT match was used to quantify inter-fraction motion. The post-treatment CBCT was matched with pre-treatment CBCT to identify any possible intra-fraction motion.ResultsDuring the molding of the mask, all patients responded positive to the comfort. Median time required by the RTTs to assemble the immobilization system was 9 min (range 6–12 min). In terms of comfort, all patients reported a good-to high level of satisfaction. The RTTs also respond positively towards the use of the locking mechanism and clips. Results of positioning uncertainties were comparable between the two institutes. The mean inter-fraction motion for all translational and rotational directions were < 2 mm (SD < 4 mm) and < 0.5°(SD < 1.5°), respectively, while the mean intra-fraction motions were < 0.4 mm (SD < 0.6 mm) and 0.3° (SD < 0.5°).ConclusionsThis study demonstrates the efficacy and feasibility of the immobilization device in the intracranial radiation treatment. Both patient comfort and preparation time by RTTs are considered adequate. In combination with online daily imaging procedure, this device can achieve submillimeter accuracy required for intracranial and stereotactic treatments.

A deep learning framework for prostate localization in cone beam CT-guided radiotherapy.

To develop a deep learning-based model for prostate planning target volume (PTV) localization on cone beam computed tomography (CBCT) to improve the workflow of CBCT-guided patient setup. A two-step task-based residual network (T2 RN) is proposed to automatically identify inherent landmarks in prostate PTV. The input to the T2 RN is the pretreatment CBCT images of the patient, and the output is the deep learning-identified landmarks in the PTV. To ensure robust PTV localization, the T2 RN model is trained by using over thousand sets of CT images with labeled landmarks, each of the CTs corresponds to a different scenario of patient position and/or anatomy distribution generated by synthetically changing the planning CT (pCT) image. The changes, including translation, rotation, and deformation, represent vast possible clinical situations of anatomy variations during a course of radiation therapy (RT). The trained patient-specific T2 RN model is tested by using 240 CBCTs from six patients. The testing CBCTs consists of 120 original CBCTs and 120 synthetic CBCTs. The synthetic CBCTs are generated by applying rotation/translation transformations to each of the original CBCT. The systematic/random setup errors between the model prediction and the reference are found to be <0.25/2.46mm and 0.14/1.41° in translation and rotation dimensions, respectively. Pearson's correlation coefficient between model prediction and the reference is higher than 0.94 in translation and rotation dimensions. The Bland-Altman plots show good agreement between the two techniques. A novel T2 RN deep learning technique is established to localize the prostate PTV for RT patient setup. Our results show that highly accurate marker-less prostate setup is achievable by leveraging the state-of-the-art deep learning strategy.

Construction reproducibility of a composite tooth model composed of an intraoral-scanned crown and a cone-beam computed tomography-scanned root.

ObjectiveTo evaluate the construction reproducibility of a composite tooth model (CTM) composed of an intraoral-scanned crown and a cone-beam computed tomography (CBCT)-scanned root.MethodsThe study assessed 240 teeth (30 central incisors, 30 canines, 30 second premolars, and 30 first molars in the maxillary and mandibular arches) from 15 young adult patients whose pre-treatment intraoral scan and CBCT were available. Examiner-Reference (3 years’ experience in CTM construction) and Examiners-A and Examiner-B (no experience) constructed the individual CTMs independently by performing the following steps: image acquisition and processing into a three-dimensional model, integration of intraoral-scanned crowns and CBCT-scanned teeth, and replacement of the CBCT-scanned crown with the intraoral-scanned crown. The tooth axis angle in terms of mesiodistal angulation and buccolingual inclination of the CTMs constructed by the three examiners were measured. To assess the construction reproducibility of CTMs, intraclass correlation coefficient (ICC) assessments were performed.ResultsThe ICC values of mesiodistal angulation and buccolingual inclination among the 3 examiners showed excellent agreement (0.950–0.992 and 0.965–0.993; 0.976–0.994 and 0.973–0.995 in the maxillary and mandibular arches, respectively).ConclusionsThe CTM showed excellent construction reproducibility in mesiodistal angulation and buccolingual inclination regardless of the construction skill and experience levels of the examiners.

Development of difficulty index for management of impacted maxillary canine: A CBCT-based study

BackgroundThe aim of this study was to propose an Impacted Canine Treatment Difficulty Index using Cone-beam Computed Tomography (CBCT) imaging to assess difficulty anticipated during the alignment of impacted maxillary canine and further validate the index in clinical set up. MethodsPre-treatment CBCT of 15 patients with unilateral or bilateral impacted maxillary canine aged between 12 and 30 years were selected. All the following five factors were assessed on CBCT image: 1) angulation, 2) vertical position, 3) bucco-palatal position, 4) horizontal position and 5) rotation. Two orthodontists evaluated the pre-treatment CBCT for the selected five factors and allocated a total difficulty score. To validate the proposed difficulty index in clinical settings, a team of oral and maxillofacial surgeons were included in the study to grade the difficulty encountered during surgical procedure. ResultsThe distribution of difficulty score recorded by observer 1 was significantly associated with the difficulty score recorded by observer 2 (P-value < 0.001), with relatively higher level of linearly weighted Cohen's kappa value of 0.610. The distribution of difficulty score recorded by oral and maxillofacial surgeon was significantly associated with the difficulty score recorded by observer 1 (P-value < 0.01), with relatively higher level of linearly weighted Cohen's kappa value of 0.667. The distribution of difficulty score recorded by orthodontist was significantly associated with the difficulty score recorded by observer 1 (P-value < 0.001), with relatively higher linearly weighted Cohen's kappa value of 0.819. ConclusionImpacted Canine Treatment Difficulty Index using CBCT imaging could be used to assess the difficulty that would be anticipated during the alignment of impacted maxillary cuspid.

Comparison of the Pharyngeal Airway Volume Between Patients With Ectodermal Dysplasia and Unaffected Controls: A Cone-Beam Computed Tomography Study

Ectodermal dysplasias (EDs) are a diverse set of hereditary conditions in which 2 or more ectodermal structures develop abnormally. The purpose of this study was to use cone-beam computed tomography (CBCT) scans to measure the pharyngeal airway volume and minimum cross-sectional area (MC) among patients with ED and compare them with healthy controls. The pretreatment CBCT scans of 9 individuals with ED and 61 controls were analyzed. Lateral cephalograms were created from the CBCT volumes and then traced and compared between the 2 groups. Airway volumes were evaluated by Dolphin 3D software (Dolphin Imaging, Chatsworth, CA) to compare the total pharyngeal volume, nasopharyngeal volume, oropharyngeal volume, hypopharyngeal volume, and MC. The mean airway volumes of the 2 groups were compared, and the odds ratio and relative risk of having an MC of less than 100mm2 in the ED group were calculated. Intraclass correlation analysis showed excellent inter-rater reliability. All cephalometric features of controls were within the norms of patients with ideal skeletal-dental relationships. Patients with ED displayed significantly lower values for SNA (angle between sella-nasion and nasion-A point) (P=.018), ANB (angle between nasion-A point and nasion-B point) (P=.002), L1-MP (angle between long axis of mandibular incisor and gonion-menton plane) (P=.013), and L1-NB (distance between mandibular incisor and perpendicular line between nasion and B point) (P<.001). Although the ED group exhibited slightly smaller airway volumes for all subregions, the differences were not statistically significant for total pharyngeal volume, nasopharyngeal volume, oropharyngeal volume, hypopharyngeal volume, or MC (P>.05). The odds of having an MC of less than 100mm2 were almost 3 times greater among ED patients, and the relative risk of an MC of less than 100mm2 among ED patients was double that of controls. Although the craniofacial structures of individuals with ED are characterized by maxillary and midface deficiency, the airway volumes among affected individuals may not be significantly different from those of unaffected controls. However, patients with ED displayed a higher risk of having an MC of less than 100mm2, which may be of clinical significance and warrants further investigations with larger samples.

Prevalence of posterior alveolar bony dehiscence and fenestration in adults with posterior crossbite: a CBCT study

BackgroundCorrecting posterior crossbite in adult patients using nonsurgical methods may involve buccolingual tooth movement. Knowing the extent of the pretreatment alveolar bony dehiscences and fenestrations in the posterior area will aid orthodontists in planning posterior crossbite patients accordingly to minimize posttreatment bony defects. Before the advent of cone beam computed tomography (CBCT), observing buccal and lingual bony defects was not possible unless other treatment needs allowed for an open-flap procedure. With CBCT technology, we can now detect posterior defects with some accuracy. The aim of the present study was to determine the prevalence of posterior alveolar bony dehiscence and fenestration in adults with posterior crossbite compared with noncrossbite adults.MethodsThe study group consisted of pretreatment CBCTs of 28 samples with at least one or more teeth in posterior crossbite or edgebite. The comparison group consisted of pretreatment CBCTs of 28 samples with no posterior crossbite or edgebite. All buccal and lingual sides of the upper and lower posterior segments were measured for the presence of dehiscence, fenestration, and combined total bony defects.ResultsThe prevalence of total bony defects was higher in the study group (61.6%) than in the comparison group (52.1%) (p < 0.05). While there was no difference in prevalence between crossbite teeth in the study group and noncrossbite teeth in the comparison group, the noncrossbite teeth in the study group showed a higher prevalence of total bony defects, dehiscence, and fenestration than the noncrossbite teeth in the comparison group (p < 0.05). The prevalence of dehiscence was higher in the study group (41.2%) than in the comparison group (33.3%) (p < 0.05). Neither the prevalence of fenestration nor the mean bony defect size showed statistical significance between the two groups. First premolars showed a higher prevalence of dehiscence than other posterior teeth, and maxillary posterior teeth had a higher prevalence of fenestration than mandibular posterior teeth. Among the maxillary posterior teeth, second premolars had the least amount of fenestration.ConclusionsAdult subjects with posterior crossbite had a higher prevalence of total bony defects and dehiscence, especially buccal dehiscence, in the posterior region than subjects with no posterior crossbite. This was due to the high prevalence observed in the noncrossbite teeth in posterior crossbite subjects.

Registration accuracy between intraoral-scanned and cone-beam computed tomography–scanned crowns in various registration methods

The purpose of this study was to investigate the registration accuracy between intraoral-scanned crowns and cone-beam computed tomography (CBCT)-scanned crowns in various registration methods. The samples consisted of 18 Korean adult patients, whose pretreatment intraoral scans and CBCT images were available. A 3-dimensional (3D) dental model was fabricated using a TRIOSintraoral scanner (3Shape, Copenhagen, Denmark) and the OrthoAnalyzer program (version 1.7.1.4; 3Shape). After the CBCT image was taken, 3D volume rendering was performed to fabricate a 3D dental model using InVivo5 software (version 5.1; Anatomage, San Jose, Calif). Registration of the 3D dental crowns made from intraoral- and CBCT-scanned images was performed with Rapidform 2006 software (Inus Technology, Seoul, Korea) by a single operator. According to registration methods, 3 groups were established: individual-arch-total-registration group, individual-arch-segment-registration group, and bimaxillary-arch-centric-occlusion-registration group (n=18 per group). After the amounts of shell/shell deviation were obtained, the mixed model analysis of variance and Bonferroni correction were performed. Although there was no significant difference in the registration accuracy between the individual-arch-total-registration group and individual-arch-segment-registration group, the bimaxillary-arch-centric-occlusion-registration group exhibited the lowest registration accuracy (maxillary and mandibular teeth, all 0.21mm in the individual-arch-total-registration group; all 0.20mm in the individual-arch-segment-registration group vs 0.26mm and 0.25mm in the bimaxillary-arch-centric-occlusion-registration group; P<0.001). Color-coded visualization charts exhibited that most red spots were localized on the occlusal surface of the posterior teeth in all 3 groups. When considering the registration accuracy and convenience of the process, the individual-arch-total-registration method can be regarded as an efficient tool when integrating CBCT-scanned crown and intraoral-scanned crown.

Residual setup errors in cranial stereotactic radiosurgery without six degree of freedom robotic couch: Frameless versus rigid immobilization systems.

Purpose and ObjectivesThis IRB‐approved study was to compare the residual inter‐fractional setup errors and intra‐fractional motion of patients treated with cranial stereotactic radiosurgery without a 6 degree of freedom (DoF) couch. We evaluated both frameless non‐invasive vacuum‐suction immobilization (Aktina PinPoint) and TALON rigid screw immobilization.Materials and MethodsTwenty consecutive patients treated by Varian TrueBeam STX or Tomotherapy were selected for data collection. The dose and number of fractions received by each patient ranged from 18 Gy in 1 fraction (SRS) to 25 Gy in 5 fractions (SRT). Twelve patients were immobilized using PinPoint, a frameless suction system (Aktina Medical, New York) and eight patients were immobilized using the TALON rigid screw system. Customized head cushions were used for all patients. Six Atkina patients received pre‐ and post‐treatment cone‐beam CT (CBCT) to evaluate the intra‐fractional motion of the Aktina system. The intra‐fractional motion with the TALON rigid screw system has been reported to be negligible and was not repeated in this study. All patients received pre‐treatment CBCT or megavoltage CT (MVCT) to assess inter‐fractional setup accuracy. Shifts to the final treatment position were determined based on matching bony anatomy in the pre‐treatment setup CT and the planning CT. Setup CT and planning CT were registered retrospectively based on bony anatomy using image registration software to quantify rotational and translational errors.ResultsFor the frameless Aktina system, mean and standard deviation of the intra‐fractional motion were −0.5 ± 0.7 mm (lateral), 0.1 ± 0.9 mm (vertical), −0.5 ± 0.6 mm (longitudinal), −0.04 ± 0.18°(pitch), −0.1 ± 0.23°(yaw), and −0.03 ± 0.17°(roll) indicating negligible intra‐fractional motion. Inter‐fractional rotation errors were −0.10 ± 0.25° (pitch), −0.08 ± 0.16° (yaw), and −0.20 ± 0.41° (roll) for TALON rigid screw immobilization versus 0.20 ± 0.69° (pitch), 0.34 ± 0.56° (yaw), 0.35 ± 0.82° (roll) for frameless vacuum‐suction immobilization showing that the rigid immobilization setup is more reproducible than the frameless immobilization. Without rotational correction by a 6 DoF couch, residual registration error exists and increases with distance from the image fusion center. In a 3D vector space, a tumor located 5 cm from the center of image fusion would require a 0.9 mm margin with the TALON system and a 2.1 mm margin with Aktina.ConclusionsWith image‐guided radiotherapy, translational setup errors can be corrected by image registration between pre‐treatment setup CT and planning CT. However, rotational errors cannot be accounted for without a 6 DoF couch. Our study showed that the frameless Aktina immobilization system provided negligible intra‐fractional motion. The inter‐fractional rotation setup error using Aktina was larger than rigid immobilization with the TALON system. To treat a single lesion far from the center of image registration or for multiple lesions in a single plan, additional margin may be needed to account for the uncorrectable rotational setup errors.

Cone-beam CT radiomics features might improve the prediction of lung toxicity after SBRT in stage I NSCLC patients.

BackgroundStereotactic body radiotherapy (SBRT) is the standard care for inoperable early stage non‐small cell lung cancer (NSCLC). The purpose of our study was to investigate whether a prediction model based on cone‐beam CT (CBCT) plus pretreatment CT radiomics features could improve the prediction of tumor control and lung toxicity after SBRT in comparison to a model based on pretreatment CT radiomics features alone.MethodsA total of 34 cases of stage I NSCLC patients who received SBRT were included in the study. The pretreatment planning CT and serial CBCT radiomics features were analyzed using the imaging biomarker explorer (IBEX) software platform. Multivariate logistic regression was conducted for the association between progression‐free survival (PFS), lung toxicity and features. The predictive capabilities of the models based on CBCT and CT features were compared using receiver operating characteristic (ROC) curves.ResultsFive CBCT features and two planning CT features were correlated with disease progression. Six CBCT features and two planning CT features were related to lung injury. The ROC curves indicated that the model based on the CBCT plus planning CT features might be better than the model based on the planning CT features in predicting lung injury. The other ROC curves indicated that the model based on the planning CT features was similar to the model based on the CBCT plus planning CT features in predicting disease progression.ConclusionsBoth pretreatment CT and CBCT radiomics features could predict disease progression and lung injury. A model with CBCT plus pretreatment CT radiomics features might improve the prediction of lung toxicity in comparison with a model with pretreatment CT features alone.Key points Significant findings of the study: A model with cone‐beam CT radiomics features plus pre‐treatment CT radiomics features might improve the prediction of lung toxicity after SBRT in stage I NSCLC patients. What this study adds: In the prediction of PFS and lung toxicity in early‐stage NSCLC patients treated with SBRT, CBCT radiomics could be another effective method.

Dosimetric impact of organ at risk daily variation during prostate stereotactic ablative radiotherapy.

Prostate stereotactic ablative radiotherapy (SABR) delivers large doses using a fast dose rate. This amplifies the effect geometric uncertainties have on normal tissue dose. The aim of this study was to determine whether the treatment dose-volume histogram (DVH) agrees with the planned dose to organs at risk (OAR). 41 low-intermediate risk prostate cancer patients were treated with SABR using a linac based technique. Dose prescribed was 35 Gy in five fractions delivered on alternate days, planned using volumetric modulated arc therapy (VMAT) with 10X flattening filter free (FFF). On treatment, prostate was matched to fiducial markers on cone beam CT (CBCT). OAR were retrospectively delineated on 205 pre-treatment CBCT images. Daily CBCT contours were overlaid on the planning CT for dosimetric analysis. Verification plan used to evaluate the daily DVH for each structure. The daily doses received by OAR were recorded using the D%. The median rectum and bladder volumes at planning were 67.1 cm3 (interquartile range 56.4-78.2) and 164.4 cm3 (interquartile range 120.3-213.4) respectively. There was no statistically significant difference in median rectal volume at each of the five treatment scans compared to the planning scan (p = 0.99). This was also the case for median bladder volume (p = 0.79). The median dose received by rectum and bladder at each fraction was higher than planned, at the majority of dose levels. For rectum the increase ranged from 0.78-1.64Gy and for bladder 0.14-1.07Gy. The percentage of patients failing for rectum D35% < 18 Gy (p = 0.016), D10% < 28 Gy (p = 0.004), D5% < 32 Gy (p = 0.0001), D1% < 35 Gy (p = 0.0001) and bladder D1% < 35 Gy (p = 0.001) at treatment were all statistically significant. In this cohort of prostate SABR patients, we estimate the OAR treatment DVH was higher than planned. This was due to rectal and bladder organ variation. OAR variation in prostate SABR using a FFF technique, may cause the treatment DVH to be higher than planned.

Observer uncertainties of soft tissue-based patient positioning in IGRT.

PurposeThere remain uncertainties due to inter‐ and intraobserver variability in soft‐tissue‐based patient positioning even with the use of image‐guided radiation therapy (IGRT). This study aimed to reveal observer uncertainties of soft‐tissue‐based patient positioning on cone‐beam computed tomography (CBCT) images for prostate cancer IGRT.MethodsTwenty‐six patients (7–8 fractions/patient, total number of 204 fractions) who underwent IGRT for prostate cancer were selected. Six radiation therapists retrospectively measured prostate cancer location errors (PCLEs) of soft‐tissue‐based patient positioning between planning CT (pCT) and pretreatment CBCT (pre‐CBCT) images after automatic bone‐based registration. Observer uncertainties were evaluated based on residual errors, which denoted the differences between soft‐tissue and reference positioning errors. Reference positioning errors were obtained as PCLEs of contour‐based patient positioning between pCT and pre‐CBCT images. Intraobserver variations were obtained from the difference between the first and second soft‐tissue‐based patient positioning repeated by the same observer for each fraction. Systematic and random errors of inter‐ and intraobserver variations were calculated in anterior–posterior (AP), superior–inferior (SI), and left–right (LR) directions. Finally, clinical target volume (CTV)‐to‐planning target volume (PTV) margins were obtained from systematic and random errors of inter‐ and intraobserver variations in AP, SI, and LR directions.ResultsInterobserver variations in AP, SI, and LR directions were 0.9, 0.9, and 0.5 mm, respectively, for the systematic error, and 1.8, 2.2, and 1.1 mm, respectively, for random error. Intraobserver variations were <0.2 mm in all directions. CTV‐to‐PTV margins in AP, SI, and LR directions were 3.5, 3.8, and 2.1 mm, respectively.ConclusionIntraobserver variability was sufficiently small and would be negligible. However, uncertainties due to interobserver variability for soft‐tissue‐based patient positioning using CBCT images should be considered in CTV‐to‐PTV margins.

Anatomic variations of the osteomeatal complex and its relationship to patency of the maxillary ostium: A retrospective evaluation of cone-beam computed tomography and its implications for sinus augmentation

Aim:The aim of this study is to determine the incidence of obliterated osteomeatal complex (OMC) due to the presence of anatomic variants.Settings and Design:Retrospective Study.Materials and Methods:In this retrospective study, a total of 71 patients, 34 males and 37 females, aged 35–65 years were included in the study. Cone beam computed tomography (CBCT) scans of patients were assessed to identify the status of the OMC in the presence of anatomic variants and their incidence was recorded. The radiological assessment of the anatomical variants was made by viewing the coronal sections of the scans. The variants observed were deviated nasal septum, uncinate process), agger nasi, Haller cells, middle turbinate variants, enlarged bulla, accessory ostium, and maxillary sinus abnormalities). Ostium patency was evaluated in the coronal section of each sinus and classified as “patent” or “obstructed.” The most common variants observed were then correlated with the patency of the ostium.Statistical Analysis Used:Chi square test was performed to assess the association between the anatomic variants and the patency of the OMC.Results:In the present study, the incidence of an obliterated OMC due to the presence of anatomic variants was 73.2%. The four most common variants associated with the possibility of an obliterated OMC were the deviated nasal septum (76.2%), middle turbinate (86.4%), enlarged bulla (77.8%), and sinus cavity variants (80.0%). A statistically significant association was noted between middle turbinate variants and Haller cells and the patency of the OMC.Conclusion:Thorough pretreatment CBCT evaluation should be performed to assess the presence of anatomic variants and thereby, the patency of the ostium before sinus floor elevation procedures. The pre and postsurgical treatment plans and regimes can be modified according to anticipated postsurgical sequelae, thereby avoiding postsurgical complications and enhancing the success of the graft procedure.

Evaluation of Mandibular Ridge Lingual Concavity Using Cone Beam Computed Tomography

Objective: To evaluate the type and depth of lingual concavity in posterior mandible using pre-treatment CBCT (Cone Beam Computed Tomography) images for dental implants. Study Design and Setting: A cross-sectional study was designed and conducted on pre-treatment CBCT scans of 75 patients at Armed Forces Institute of Dentistry, Rawalpindi, Pakistan from February 2018 to November 2018. Methodology: Pre-treatment CBCT scans of 75 patients were selected and following parameters were measured: type of ridge (undercut, parallel, convex), ridge width, ridge height, depth of lingual concavity, concavity angle, and location of the undercut. Data was analyzed using SPSS version .24. Post-stratification Mann-Whitney U test was used for effect modifiers, while Kruskal-Wallis test was used to compare study parameters between groups. P value &lt;0.05 was taken as significant. Results: A mean concavity depth of 1.17±1.40 mm was observed while majority (46.7%) of the CBCT images presented with undercut type ridge. No significant difference was observed between males and females for any study parameter. Conclusion: Undercut ridges were frequently observed, posing a threat of lingual perforation during implant placement. Pre-operative assessment of implant site using CBCT can serve as a reliable method to avoid such complications

CONE BEAM COMPUTED TOMOGRAPHIC ASSESSMENT OF THE DISTANCE BETWEEN THE INCISIVE CANAL AND MAXILLARY CENTRAL INCISORS

Background Maxillary anterior teeth play an important role in aesthetics, phonetics, and mastication. Because of the aesthetic and functional significance, it is important to evaluate their position in association with surrounding structures in 3-D before initiating orthodontic treatment. With the advent of cone beam computed tomography (CBCT) in orthodontic diagnosis, it is now possible to identify these structures. One such structure is the incisive canal. Uncertainty in locating the canal can cause root resorption postorthodontic retraction of anterior maxillary teeth. Objective(s) The aim of this study was to calculate the relative distance between the incisive canal and maxillary central incisor using CBCT and utilize the results for orthodontic treatment planning. Study Design All quantitative measurements between the incisive canal and both maxillary central incisors were performed using CBCT on 61 patients. The anteroposterior measurements were taken on both sides, and the average of both values was considered for the statistical analysis. The Steiner cephalometric analysis was performed to select patients with skeletal and dental Class I relationship. All linear measurements were performed on the axial plane at 3 different vertical reference points located on the sagittal plane: (1) the palatal opening of the incisive canal (opening level, P1), (2) midlevel between the opening level and the root apex of the maxillary central incisors (midlevel, P2), and (3) the root apex of the maxillary central incisors (root apex level, P3). Results The average anteroposterior distance between the maxillary central incisor roots and the incisive canal was approximately 56 mm. Discussion/Conclusions The results of our study could be clinically helpful to plan orthodontic treatment that requires significant retraction of maxillary incisors. The authors support the idea of a pretreatment CBCT in cases that require maximum anterior retraction in the maxilla. Maxillary anterior teeth play an important role in aesthetics, phonetics, and mastication. Because of the aesthetic and functional significance, it is important to evaluate their position in association with surrounding structures in 3-D before initiating orthodontic treatment. With the advent of cone beam computed tomography (CBCT) in orthodontic diagnosis, it is now possible to identify these structures. One such structure is the incisive canal. Uncertainty in locating the canal can cause root resorption postorthodontic retraction of anterior maxillary teeth. The aim of this study was to calculate the relative distance between the incisive canal and maxillary central incisor using CBCT and utilize the results for orthodontic treatment planning. All quantitative measurements between the incisive canal and both maxillary central incisors were performed using CBCT on 61 patients. The anteroposterior measurements were taken on both sides, and the average of both values was considered for the statistical analysis. The Steiner cephalometric analysis was performed to select patients with skeletal and dental Class I relationship. All linear measurements were performed on the axial plane at 3 different vertical reference points located on the sagittal plane: (1) the palatal opening of the incisive canal (opening level, P1), (2) midlevel between the opening level and the root apex of the maxillary central incisors (midlevel, P2), and (3) the root apex of the maxillary central incisors (root apex level, P3). The average anteroposterior distance between the maxillary central incisor roots and the incisive canal was approximately 56 mm. The results of our study could be clinically helpful to plan orthodontic treatment that requires significant retraction of maxillary incisors. The authors support the idea of a pretreatment CBCT in cases that require maximum anterior retraction in the maxilla.

Quantifying the Intra-fraction Treatment Variation in the Shift Off Bone in Fiducial-Based IG-SBRT for Pancreatic Adenocarcinoma

Given the proximity of the radio-sensitive bowel, stereotactic body radiotherapy (SBRT) for pancreatic cancer requires precise immobilization and target localization, which can allow for steeper dose gradients and tighter margins. Currently, however, wide variation exists in the selection of planning target volume (PTV) margins that should be used in this setting. As intra-fraction variation represents a primary component of an appropriate PTV margin, we present our experience with intra-fraction shifts required during pancreatic SBRT, which has not previously been characterized in the literature. We analyzed 30 consecutively patients treated with SBRT for pancreatic cancer at our institution using volumetric modulated arc therapy (VMAT), active breathing control (ABC), and image-guided (IG) cone-beam computed tomography (CBCT). Patients were initially aligned to bony landmarks and then shifted to fiducials that had been endoscopically-placed. Halfway through treatment, an intra-fraction CBCT was obtained. Using the pre-treatment and intra-fraction CBCT, with the spine as a reference point, we calculated the intra-fraction shift in each axis along with a three-dimensional (3D) vector shift. The mean, maximum, and standard deviation of the intra-fraction shift in each direction, including the 3D vector, were calculated for individual patients across the five fractions. Population averages and standard deviations of each of these metrics were also calculated. Additionally, a linear regression model was developed to understand if the pre-treatment shift from bone to fiducial was related to the intra-fraction shift. On average, the mean intra-fraction shifts in the L-R, A-P, and S-I directions were 1.91± 0.82 mm, 1.62 ± 0.70 mm, and 2.33 ± 1.45 mm, respectively, and the mean intra-fraction shift as a 3D vector was 4.06 ± 1.51 mm. On average, the maximum intra-fraction shifts in the L-R, A-P, and S-I directions were 4.41 ± 2.37 mm, 3.51 ± 1.68 mm and 5.22 ± 3.79 mm, and the maximum intra-fraction shift as a 3D vector was 7.46 ± 3.70 mm. The linear regression model identified a statistically significant relationship between the mean pre-treatment shift from bone to fiducial and the mean intra-fraction shift in the A-P (p = 0.003) and S-I (p = 0.004) directions, along with for the 3D vector (p = 0.019). We report a single-institutional experience with intra-fractions shifts for patients undergoing SBRT for pancreatic cancer. These values can better inform appropriate PTV margins. As an example, to ensure a 95% likelihood that the target is encompassed within the PTV throughout treatment, radial margins of roughly 3-3.5mm and an SI margin of roughly 5mm should be considered. However, more data across institutions and using different motion management strategies is required for more generalizable results.

Residents' journal review

Residents' journal review

Midpalatal suture maturation assessment by individuals with different levels of academic degree using cone beam computed tomography

Objective: Our aim was to analyze the reliability of midpalatal suture maturation assessment in females in the final growth period using cone-beam computed tomography (CBCT) by an undergraduate student in two time periods (intraexaminer) and compared to an orthodontist (inter-examiner). Methods: Forty pretreatment CBCT images of 14 to 19-year-old females were selected. Images were oriented in the InVivo Dental 5.1 software. Axial slices were selected either by a researcher (preselected slices – suture-PS) or by the examiners (free scanning and slice selection – suture-FS) and each image was classified according to itsmidpalatal suture maturation stage. The examiners analyzed all images individually and twice, with a two-week interval between sessions. The weighted kappa coefficient according to Landis and Kock was used to assess intra- and inter-examiner agreement. Results: The Kappa intra-examiner of the undergraduate student was 0.824 for suture-PS and 0.692 for suture-FS, and the orthodontist was 0.919 and 0.695, respectively. Inter-observer agreement was higher for suture-PS (>0.479) than for suture-FS (>0.300). Conclusion: The intraobserver kappa coefficient was very good for the undergraduate student, similarto the orthodontist. However, inter-examiner agreement was not good, indicating a need for development in the method training.

An augmented correlation framework for the estimation of tumour translational and rotational motion during external beam radiotherapy treatments using intermittent monoscopic x-ray imaging and an external respiratory signal

Increasing evidence shows that intrafraction tumour motion monitoring must include both six degrees of freedom (6DoF): 3D translations and 3D rotations. Existing real-time algorithms for 6DoF target motion estimation require continuous intrafraction fluoroscopic imaging at high frequency, thereby exposing patients to additional high imaging dose. This paper presents the first method capable of 6DoF motion monitoring using intermittent 2D kV imaging and a continuous external respiratory signal.Our approach is to optimise a state-augmented linear correlation model between an external signal and internal 6DoF motion. In standard treatments, the model can be built using information obtained during pre-treatment cone beam CT (CBCT). Real-time 6DoF tumor motion can then be estimated using just the external signal. Intermittent intrafraction kV images are used to update the model parameters, accounting for changes in correlation and baseline shifts.The method was evaluated in silico using data from 6 lung SABR patients, with the internal tumour motion recorded with electromagnetic beacons and the external signal from a bellows belt. Projection images from CBCT (10 Hz) and intermittent kV images were simulated by projecting the 3D Calypso beacon positions onto an imager. IMRT and VMAT treatments were simulated with increasing imaging update intervals: 0.1 s, 1 s, 3 s, 10 s and 30 s.For all the tested clinical scenarios, translational motion estimates with our method had sub-mm accuracy (mean) and precision (standard deviation) while rotational motion estimates were accurate to < and precise to . Motion estimation errors increased as the imaging update interval increased. With the largest imaging update interval (30 s), the errors were mm, mm and mm for translation in the left–right, superior–inferior and anterior–posterior directions, respectively, and , and for rotation around the aforementioned axes for both VMAT and IMRT treatments.In conclusion, we developed and evaluated a novel method for highly accurate real-time 6DoF motion monitoring on a standard linear accelerator without requiring continuous kV imaging. The proposed method achieved sub-mm and sub-degree accuracy on a lung cancer patient dataset.