Inferior Direction Research Articles

Lamina cribrosa pore movement during acute intraocular pressure rise

PurposeTo assess changes in the position of lamina cribrosa pores (LCPs) induced by acute intraocular pressure (IOP) elevation.MethodsA prospective observational study. Acute angle-closure suspects who underwent the 2-hour dark room...

Early Clinical Experience with Varian Halcyon V2 Linear Accelerator: Dual -Isocenter IMRT Planning and Delivery with Portal Dosimetry for Gynecological Cancer Treatments

A linear accelerator was recently released with new upgraded features. One of new features is to allow treatment length > 28cm using multiple- isocenters (maximum of 36cm in superior and inferior directions). As one of the first users of Halcyon V2, we report our clinical experience with Halcyon V2 for a dual - isocenter IMRT planning and delivery for gynecological cancer patients and examine the feasibility of in-vivo portal dosimetry. Eight extended field IMRT plans for gynecological cancer patients were generated with a treatment planning system using two isocenters to treat pelvis and pelvic/or para-aortic nodes region. Auto feathering technique was employed to split fields between isocenters during IMRT optimization. The prescription dose was 45Gy in 25 fractions (fxs) with simultaneous integrated boost (SIB) dose of 55Gy or 57.5 Gy in 25 fxs to involved nodes. All treatment plans, pre-treatment patient specific QA and treatment delivery records including daily in-vivo portal dosimetry were retrospectively reviewed. For in-vivo daily portal dosimetry analysis, each fraction was compared to the reference baseline (1st fraction) using gamma analysis criteria of 4%/4mm with 90% of total pixels in the portal image planar dose. All 8 extended field IMRT plans met the planning criteria and delivered as planned (a total of 200 fractions). Conformity Index (CI) for the primary target was achieved with the range of 0.99-1.14. For organs at risks, most were well within the dose volume criteria. Treatment delivery took from 5.0 to 6.5 minutes. All 8 cases passed pre-treatment QA using gamma analysis criteria of 3%/2mm with 95 % of total pixels. Interfractional in-vivo dose variation exceeded gamma analysis threshold for 8 fractions out of total 200 (4%). Those 8 fractions were found to have relatively large difference in small bowel filling or motion and SSD change at the isocenter compared to the baseline. Halcyon V2 is effective to create complex extended field IMRT plans using dual isocenters with efficient delivery. Also Halcyon in-vivo dosimetry is feasible for daily treatment monitoring for possible (or significant) changes of organ motion, internal or external anatomy and weight which could further lead to adaptive radiation therapy.

Anatomical deformation due to horizontal rotation: towards gantry-free radiation therapy

Gantry-free radiation therapy systems may be simpler and more cost effective, particularly for MRI-guided photon or hadron therapy. This study aims to understand and quantify anatomical deformations caused by horizontal rotation with scan sequences sufficiently short to facilitate integration into an MRI-guided workflow.Rigid and non-rigid pelvic deformations due to horizontal rotation were quantified for a cohort of 8 healthy volunteers using a bespoke patient rotation system and a clinical MRI scanner. For each volunteer a reference scan was acquired at 0° followed by sequential faster scans in 45° increments through to 360°. All fast scans were registered to the 0° image via a three-step process: first, images were aligned using MR visible couch markers. Second, the scans were pre-processed then rigidly registered to the 0° image. Third, the rigidly registered scans were non-rigidly registered to the 0° image to assess soft tissue deformation. The residual differences after rigid and non-rigid registration were determined from the transformation matrix and the deformation vector field, respectively.The rigid registration yielded mean rotations of ⩽2.5° in all cases. The average 3D translational magnitudes range was 5.8 ± 2.9 mm–30.0 ± 11.0 mm. Translations were most significant in the left–right (LR) direction. Smaller translations were observed in the anterior–posterior (AP) and superior–inferior (SI) directions. The maximum deformation magnitudes range was: 10.0 ± 0.9 mm–28.0 ± 2.8 mm and average deformation magnitudes range: 2.3 ± 0.6 mm–7.5 ± 1.0 mm. Average non-rigid deformation magnitude was correlated with BMI (correlation coefficient 0.84, p = 0.01).Rigid pelvic deformations were most significant in the LR direction but could be accounted for with on-line adjustments. Non-rigid deformations can be significant and will need to be accounted for in order to facilitate the delivery of gantry-free therapy with an automated patient rotation system.

Use of a Heister mouth gag as an aid to reduction in open treatment of condylar fracture.

The management of condylar fractures remains controversial. Open treatment of condylar fractures is a routine treatment in cases of displaced or dislocated condylar and subcondylar fractures. Because of the pull of the lateral pterygoid muscle, the condylar fragment is usually located anterior and medial to the mandible. Distraction of the mandible in an inferior direction simplifies proper reduction. Various distraction devices have been described in literature. We describe a technique of using the Heister mouth gag at the surgical site to aid in reduction of displaced dislocated condylar fractures.

Peripheral nerve stimulation limits of a high amplitude and slew rate magnetic field gradient coil for neuroimaging.

To establish peripheral nerve stimulation (PNS) thresholds for an ultra-high performance magnetic field gradient subsystem (simultaneous 200-mT/m gradient amplitude and 500-T/m/s gradient slew rate; 1 MVA per axis [MAGNUS]) designed for neuroimaging with asymmetric transverse gradients and 42-cm inner diameter, and to determine PNS threshold dependencies on gender, age, patient positioning within the gradient subsystem, and anatomical landmarks. The MAGNUS head gradient was installed in a whole-body 3T scanner with a custom 16-rung bird-cage transmit/receive RF coil compatible with phased-array receiver brain coils. Twenty adult subjects (10 male, mean ± SD age = 40.4 ± 11.1 years) underwent the imaging and PNS study. The tests were repeated by displacing subject positions by 2-4 cm in the superior-inferior and anterior-posterior directions. The x-axis (left-right) yielded mostly facial stimulation, with mean ΔGmin = 111 ± 6 mT/m, chronaxie = 766 ± 76 µsec. The z-axis (superior-inferior) yielded mostly chest/shoulder stimulation (123 ± 7 mT/m, 620 ± 62 µsec). Y-axis (anterior-posterior) stimulation was negligible. X-axis and z-axis thresholds tended to increase with age, and there was negligible dependency with gender. Translation in the inferior and posterior directions tended to increase the x-axis and z-axis thresholds, respectively. Electric field simulations showed good agreement with the PNS results. Imaging at MAGNUS gradient performance with increased PNS threshold provided a 35% reduction in noise-to-diffusion contrast as compared with whole-body performance (80 mT/m gradient amplitude, 200 T/m/sec gradient slew rate). The PNS threshold of MAGNUS is significantly higher than that for whole-body gradients, which allows for diffusion gradients with short rise times (under 1 msec), important for interrogating brain microstructure length scales.

The influence of hand location and handle orientation on female manual arm strength

Accurate estimations of manual arm strength (MAS) are crucial in the evaluation of occupational force demands relative to population capacity. Most current strength predictions assume force application with a vertically oriented handle, but it is unknown how uni-manual force capability changes as a function of handle orientation and hand location. This study evaluated the effect of handle orientation on MAS throughout the reach envelope. Fifteen female participants exerted maximum forces in six directions (i.e. superior, inferior, anterior, posterior, medial, lateral), at five different hand locations, and MAS was measured with the handle oriented at 0° (i.e. horizontal), 45°, 90° (i.e. vertical) and 135°. Handle orientation affected MAS in all but the anterior exertion direction, with significant interactions between hand location and grip orientation existing for the superior and inferior directions. These results suggest that handle orientation is important to consider in future predictive models of manual arm strength.

Conical beam geometry intensity-modulated radiation therapy

Most commonly in radiation therapy, treatments are delivered in a co-planar geometry. Numerous advantages have been reported of adding non-coplanar beams to the treatment plan. The aim of this study was to compare current state-of-the-art VMAT and CyberKnife treatment plans to that of a novel linac design developed at Stanford which utilizes a static conical beam arrangement that allows the inclusion of a full ring diagnostic CT with shared isocenter with the treatment beams.Four clinical cases, prostate, lung, head/neck, and pediatric brain, were selected and treatment plans were generated with 45° or 60° (to the longitudinal axis of the patient) conical beam IMRT and compared with co-planar 90° VMAT plans. Double cone, with beams entering from both superior and inferior directions, and single cone geometries were evaluated. Plans were optimized in RayStation using an in-house developed script to minimize operator bias between the different techniques. Non-coplanar CyberKnife IMRT plans for the pediatric and prostate case were optimized separately in MultiPlan and compared to conical geometry plans.In the prostate case, increased mean dose to the rectum (2.3–3.7 Gy) and bladder (9.5–14.5 Gy) but decreased dose to the femoral heads (femurs) (7.1–10 Gy) were found with the conical arrangement compared to 90° VMAT. Only minor dosimetric differences were found in the lung case, while selective sparing of organs at risk was found with 45° or 60° conical arrangement in the pediatric brain and head/neck cases. For the prostate case, a reduction in mean doses to the bladder and rectum of 6% (2 Gy) and 18% (5.2 Gy), respectively, was found when comparing the CyberKnife to the 60° conical plan, in favor of the CyberKnife plan, but with an increase in integral dose and reduced conformity. An increase in integral dose and reduced conformity was also found for the pediatric brain case when comparing CyberKnife and 60° conical plan. Minor benefits were found with double cone compared to single cone geometry.Comparable treatment plan quality could be achieved between conical beam arrangement and 90° (coplanar) VMAT and CyberKnife (non-coplanar) IMRT, demonstrating the promise of this novel beam geometry. The use of this beam geometry allows volumetric image-guidance with full ring imaging and a common isocenter for simultaneous treatment and imaging.

Correlation of displacement of mediastinal metastatic lymph nodes with adjacent organs in non‐small cell lung cancer on four‐dimensional computed tomography

AbstractObjectiveTo determine the correlation of displacement of the mediastinal metastatic lymph nodes with adjacent organs in non‐small cell lung cancer using four‐dimensional computed tomography.MethodsThe displacements of 51 mediastinal metastatic lymph nodes located in the left–right, anterior–posterior, and superior–inferior directions were measured using four‐dimensional computed tomography. Correlation analyses were carried out to determine the association between the displacement of lymph nodes and volumetric change of the lungs and heart.ResultsA significant correlation of displacement of the left group lymph nodes in left–right and the right group in anterior–posterior directions with volumetric change of the ipsilateral lung was observed. There were significant correlations between displacement of the left group lymph nodes and volumetric change of the heart.ConclusionDisplacement of the mediastinal metastatic lymph nodes was relevant to the adjacent organs.

Dosimetric impact of esophagus motion in single fraction spine stereotactic body radiotherapy

Nine patients with single fraction spinal stereotactic body radiation therapy (SBRT) treatment were identified to assess both the intra fraction and daily esophageal motion and associated dosimetric deviation in spinal SBRT. We performed a chained deformable registration of 4D CT phase images to estimate the intra fraction motion magnitude of the esophagus in a breathing cycle. The intra fraction esophageal motion mostly exhibited in the superior–inferior direction with the total motion magnitude increased from the T1 (0.7 mm) to the T11 vertebra level (6.5 mm). The actual dose received by a moving esophagus was estimated by accumulating dose from each phase of the 4D dataset using deformable image registration. In comparison, dose recalculated on the average CT reflects the dose received by a stationary esophagus. Intra fraction motion was found to reduce the maximum dose received by a small volume of esophagus ⩽2 cm3, with the largest absolute and relative dose difference being −80 cGy and −6.4%, respectively. Its effect on the maximum dose received by 5 cm3 of esophagus can be higher or lower with a large percentage difference, but did not result in substantial absolute dose increase to violate the dose constraint of 11.9 Gy we used for plan evaluation. In addition, there was no correlation between the dosimetric deviation and the intra fraction motion magnitude. These findings suggest that 4D CT simulation is not essential with regards to the esophageal dose. The daily motion of the esophagus and its dosimetric impact was investigated by examining the difference of esophagus delineated on both treatment and planning CT after they were registered using boney target. The day to day difference of esophagus was negligible for all cases in this study.

First clinical retrospective investigation of limited projection CBCT for lung tumor localization in patients receiving SBRT treatment

To clinically investigate the limited-projection CBCT (LP-CBCT) technology for daily positioning of patients receiving breath-hold lung SBRT radiation treatment and to investigate the feasibility of reconstructing fast 4D-CBCT from 1 min 3D-CBCT scan.Eleven patients who underwent breath-hold lung SBRT radiation treatment were scanned daily with on-board full-projection CBCT (CBCT) using half-fan scan. A subset of the CBCT projections and the prior planning CT were used to estimate the LP-CBCT images using the weighted free-form deformation method. The limited projections are clusteringly sampled within fifteen sub-angles in 360° in order to simulate the fast 1 min scan for 4D-CBCT. The estimated LP-CBCTs were rigidly registered to the planning CT to determine the clinical shifts needed for patient setup corrections, which were compared with shifts determined by the CBCT for evaluation. Both manual and automatic registrations were performed in order to compare the systematic registration errors. Fifty CBCT volumes were obtained from the eleven patients in fifty fractions for this pilot clinical study.For the CBCT images, the mean (±standard deviation) shifts between CBCT and planning CT from manual registration in left–right (LR), anterior–posterior (AP), and superior–inferior (SI) directions are 1.1 ± 1.2 mm, 2.1 ± 1.9 mm, 5.2 ± 3.6 mm, respectively. The mean deviation difference between shifts determined by CBCT and LP-CBCT images are 0.3 ± 0.5 mm, 0.5 ± 0.8 mm, 0.4 ± 0.3 mm, in LR, AP, and SI directions, respectively. The mean vector length of CBCT shift for all fractions is 6.1 ± 3.6 mm, and the mean vector length difference between CBCT and LP-CBCT for all fractions studied is 1.0 ± 0.9 mm. The automatic registrations yield similar results as manual registrations.The pilot clinical study shows that LP-CBCT localization offers comparable accuracy to CBCT localization for daily tumor positioning while reducing the projection number to 1/10 for patients receiving breath hold lung radiation treatment. The cluster projection sampling in this study also shows the feasibility of reconstructing fast 4D-CBCT from 1 min 3D-CBCT scan.

Focus on the Importance of Lipomid-Abdominoplasty in the Body Contouring Surgery.

During the last few years, the surgical principles of abdominoplasty remained unchanged. Therefore, many observed results have misaligned, high and straight abdominal transverse scars, leading to the final positioning of the umbilical scar to be very close to the transverse scar, which gives the impression of a short abdomen. We propose that the abdominoplasty should change the basic conception of its marking, because we believe that it is important to place the transverse scar lower in the medial and pubic region, and higher in the lateral extremities, thus allowing a rotation of the flap of the anterior flanks back lumbar in the median inferior direction. We analyzed 136 patients with abdominal deformities and subjected them to lipomid-abdominoplasty making a marking with strong upper concavity and lateral sides of the scar oriented to the lower transverse line of the abdomen, 4cm equidistant from the root of the thigh. We also associate liposuction as a complementary treatment to body contouring. It is important to determine the area of the abdominal deformity and its classification, to establish the strategies of treatment, and association of complementary procedures. A lower marking respecting the treatment areas will allow a better esthetic scar and a harmonic body contour as well as an adequate placement of the elements: umbilical scar, pubis and lateral extremities of transverse abdominal scar. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Dose fall-off patterns with volumetric modulated arc therapy and three-dimensional conformal radiotherapy including the “organ at risk” effect. Experience of linear accelerator-based frameless radiosurgery from a single institution

PurposeThis study aimed to evaluate characteristics of dose fall-off pattern for linear accelerator based frameless stereotactic radiotherapy and radiosurgery using two different techniques, three-dimensional conformal radiotherapy and volumetric modulated arc therapy. Materials and methodsThe data from thirty patients who underwent frameless stereotactic radiotherapy/radiosurgery were considered for this analysis. These included 11 patients treated using three-dimensional conformal radiation and 19 patients treated with volumetric modulated arc therapy. Dose fall-offs in six predetermined directions from the edge of planning target volume and in direction of organs at risk were evaluated. These included determining dose fall-off (distance range) of 100%–80%, 100%–50%, 100%–20% from the treatment planning system. The first derivative (percentage of dose fall-off per millimetre) and second derivative (percentage of dose per square millimetre) of the dose fall-off was calculated. ResultsThe dose fall-off is sharpest in the organ at risk direction if the organ at risk is hugging the planning target volume. However, for organs at risk separated from the planning target volume sharpest dose fall-off could be in either planning target volume superior or inferior direction. Three-dimensional conformal radiotherapy plans had a mean±SD of 14±2 beams (range: 11–17). Volumetric modulated arc therapy planning comprised of arc angles with sum±SD of 953±172.5° (range: 610°–1170°). Mean±SD for the single sharpest dose fall-off for all patients receiving three-dimensional conformal radiotherapy was 11.3±4.7%·mm−1, 7.8±4.8%·mm−1 and 7.1±5.6%·mm−1 for 100%–80%, 100%–50% and 100%–20% fall-off ranges respectively. For volumetric modulated arc therapy, the mean±SD of the single sharpest fall-off was 10.4±4.6%·mm−1, 7.8±3.0%·mm−1 and 7.3±5.0%·mm−1 for 100%–80%, 100%–50% and 100%–20% range. All organs at risk doses received doses within limits prescribed by AAPM-TG report 21. Mean dose to monitor units (MU) modulation factor MF=total MU deliveredprescription dose in cGy for three-dimensional conformal radiotherapy and volumetric modulated arc therapy were 1.97±1.0 MU·cGy−1 and 2.5±0.75 MU·cGy−1 respectively. ConclusionOur study presents the dose fall-off patterns in context of frameless stereotactic radiation therapy. We have presented the dose fall-off data in the framework of three-dimensional conformal radiotherapy and volumetric modulated arc therapy in brain lesions.

Automatic calibration of an arbitrarily-set near-infrared camera for patient surface respiratory monitoring.

A patient's respiratory monitoring is one of the key techniques in radiotherapy for a moving target. Generally, such monitoring systems are permanently set to a fixed geometry during the installation. This study aims to enable a temporary setup of such a monitoring system by developing a fast method to automatically calibrate the geometrical position by a quick measurement of calibration markers. One calibration marker was placed on the isocenter and the other six markers were placed at positions 5-cm apart from the isocenter to the left, right, anterior, posterior, superior, and inferior directions. A near-infrared (NIR) camera (NIC) [Kinect v2 (Microsoft Corp.)] was arbitrarily set with ten different angles around the calibration phantom with a fixed tilting-down angle at approximately 45° in a linear accelerator treatment vault. The three-dimensional (3D) coordinates in the camera (Cam) coordinate system (CS; and are the horizontal and vertical coordinates of the image, respectively, and is a coordinate along the NIR time-of-flight) were taken for 1min with 30 frames per second. The data corresponding to the measurement times of 1, 3, 10, 30, and 60s were created to mimic various measurement times. These data were used to calculate the initial matrix elements, which included six parameters of the pitching, yawing, and rolling angles; horizontal two-dimensional translation in the treatment room; and the source-to-axis distance of NIC, for a conversion from the Cam CS to the treatment room CS for which the origin was defined at the isocenter (Iso coordinate). The six parameters were then optimized to minimize the displacements of the calculated marker coordinates from the actual positions in the Iso CS. The 3D positional accuracy and angular accuracy of the conversion were evaluated. The random error of the Iso coordinates was analyzed through a relation with the angle of each measurement setup. Three angles of NIC and relative translation vectors were successfully calculated from the measurement data of the calibration markers. The achieved spatial and angular accuracies were 0.02mm and 1.6°, respectively, after the optimization. Among the mimicked measurement times investigated in this study, both spatial and angular accuracies had no dependence on the measurement time. The average random error of a static marker was 0.46mm after the optimization. We developed an automatic method to calibrate the 3D patient surface monitoring system. The procedure developed in this study enabled a quick calibration of NIC, which can be easily repeated multiple times for a frequent and quick setup of the monitoring system.

Intradural Subtemporal Keyhole Approach with Neuronavigational Assistance to the Petroclival and Ventrolateral Brainstem Regions: Quantitative Analysis of Anatomic Exposure and Surgical Freedom

The purpose of this study was to evaluate the advantages of endoscopy and navigational assistance in the intradural subtemporal keyhole approach and the intradural Kawase approach by studying anatomic exposure and surgical freedom in the posterior cranial fossa. Twenty endoscopic intradural subtemporal keyhole approaches (EISKA) were performed on 10 cadaveric heads. An intradural Kawase approach and a navigation-assisted intradural Kawase approach were then carried out on a random side of each specimen. Related anatomic structures were observed through a 0° endoscope and a microscope. Anatomic exposure and surgical freedom were measured by transparent graph paper and analyzed. Compared with the microsurgical technique, the superior, inferior, and medial limits of the endoscopic anatomic exposure increased by 2.9, 15.65, and 10.2 mm, whereas the surgical freedom increased by 2.9, 7.55, and 6 mm (P < 0.05) in the intradural subtemporal keyhole approach. In the intradural Kawase approach and the navigation-assisted intradural Kawase approach, the endoscopic anatomic exposure and surgical freedom also increased (P < 0.05). Using a frameless navigational device, the inferior limit of the anatomic exposure increased 3.8 mm by endoscopy and 3.5 mm by microscopy, whereas the surgical freedom increased by 2.7 and 2.2 mm, respectively (P < 0.05). The EISKA provides greater anatomic exposure and surgical freedom primarily in the superior, inferior, and medial directions of the brainstem region. Maximum anatomic exposure and surgical freedom of the posterior cranial fossa was obtained by navigational assistance with fewer complications.

ELPHA: Dynamically deformable liver phantom for real-time motion-adaptive radiotherapy treatments.

Real-time motion-adaptive radiotherapy of intrahepatic tumors needs to account for motion and deformations of the liver and the target location within. Phantoms representative of anatomical deformations are required to investigate and improve dynamic treatments. A deformable phantom capable of testing motion detection and motion mitigation techniques is presented here. The dynamically dEformable Liver PHAntom (ELPHA) was designed to fulfill three main constraints: First, a reproducibly deformable anatomy is required. Second, the phantom should provide multimodality imaging contrast for motion detection. Third, a time-resolved dosimetry system to measure temporal effects should be provided. An artificial liver with vasculature was casted from soft silicone mixtures. The silicones allow for deformation and radiographic image contrast, while added cellulose provides ultrasonic contrast. An actuator was used for compressing the liver in the inferior direction according to a prescribed respiratory motion trace. Electromagnetic (EM) transponders integrated in ELPHA help provide ground truth motion traces. They were used to quantify the motion reproducibility of the phantom and to validate motion detection based on ultrasound imaging. A two-dimensional ultrasound probe was used to follow the position of the vessels with a template-matching algorithm. This detected vessel motion was compared to the EM transponder signal by calculating the root-mean-square error (RMSE). ELPHA was then used to investigate the dose deposition of dynamic treatment deliveries. Two dosimetry systems, radio-chromic film and plastic scintillation dosimeters (PSD), were integrated in ELPHA. The PSD allow for time-resolved measurement of the delivered dose, which was compared to a time-resolved dose of the treatment planning system. Film and PSD were used to investigate dose delivery to the deforming phantom without motion compensation and with treatment-couch tracking for motion compensation. ELPHA showed densities of 66 and 45HU in the liver and the surrounding tissues. A high motion reproducibility with a submillimeter RMSE (<0.32mm) was measured. The motion of the vasculature detected with ultrasound agreed well with the EM transponder position (RMSE<1mm). A time-resolved dosimetry system with a 1Hz time resolution was achieved with the PSD. The agreement of the planned and measured dose to the PSD decreased with increasing motion amplitude: A dosimetric RMSE of 1.2, 2.1, and 2.7cGy/s was measured for motion amplitudes of 8, 16, and 24mm, respectively. With couch tracking as motion compensation, these values decreased to 1.1, 1.4, and 1.4cGy/s. This is closer to the static situation with 0.7cGy/s. Film measurements showed that couch tracking was able to compensate for motion with a mean target dose within 5% of the static situation (-5% to +1%), which was higher than in the uncompensated cases (-41% to -1%). ELPHA is a deformable liver phantom with high motion reproducibility. It was demonstrated to be suitable for the verification of motion detection and motion mitigation modalities. Based on the multimodality image contrast, a high accuracy of ultrasound based motion detection was shown. With the time-resolved dosimetry system, ELPHA is suitable for performance assessment of real-time motion-adaptive radiotherapy, as was shown exemplary with couch tracking.

Finite Element Analysis of Stress in Maxillary Dentition during En-masse Retraction with Implant Anchorage.

The goal of this study was to investigate how the height of the archwire hook and implant anchor affect tooth movement, stress in the teeth and alveolar bone, and the center of resistance during retraction of the entire maxillary dentition using a multibracket system. Computed tomography was used to scan a dried adult human skull with normal occlusion. Three-dimensional models of the maxillary bone, teeth, brackets, archwire, hook, and implant anchor were created and used for finite element analysis. The heights of the hook and the implant anchor were set at 0, 5, or 10 mm from the archwire. Orthodontic force of 4.9 N was systematically applied between the hook and the implant anchor and differential stress distributions and tooth movements observed for each traction condition. With horizontal traction, the archwire showed deformation in the superior direction anterior to the hook and in the inferior direction posterior to the hook. Differences in traction height and direction resulted in different degrees of deformation, with biphasic movement clearly evident both in front of and behind the hook. With horizontal traction of the hook at a height of 0 mm, all the teeth moved distally, but not with any other type of traction. At a height of 5 mm or 10 mm, deformation showed an increase. The central incisor showed extrusion under all traction conditions, with the amount showing a reduction as the height of horizontal or posterosuperior traction increased. The center of resistance was located at the root of the 6 anterior teeth and entire maxillary dentition. The present results suggest that it is necessary to consider deformation of the wire and the center of resistance during en-masse retraction with implant anchorage.

Primary Tumor Extension Probability-based Prediction of Individualized Clinical Target Volume for Nasopharyngeal Carcinoma

To establish a primary tumor extension probability knowledge base and develop a probability-based clinical tumor volume (CTV) prediction model for nasopharyngeal carcinoma (NPC). One thousand patients with newly histologically confirmed, non-disseminated NPC between January 2010 and December 2011 were included in this study. For all patients, primary gross tumor volumes (GTVp) displayed on pre-treatment magnetic resonance (MR) images were manually superimposed onto a single computed tomography (CT) scan. Tumor extension probability of each CT voxel was calculated to form a knowledge base. Then association rules mining algorithm was implemented to develop a probability-based CTV prediction model. One hundred cases were randomly selected from the patient cohort to evaluate similarity and variance between predicted CTV and expert delineation, which were manually completed by 2 radiation oncologists by consensus. Similarity was evaluated using Dice similarity coefficient (DSC), and variance using mean distances from GTVp to CTV in anterior, posterior, lateral, superior and inferior directions. Five multicenter radiation oncologists and another randomly selected 16 cases were included in a multicenter setting to evaluate the similarity between edited predicted CTV and expert delineation against that between manual delineation and expert delineation. Besides, inter-observer variance of 5 oncologists’ delineation was assessed using multi-observer DSC, and time spent on manual delineation and in editing predicted CTV were also reported. For 1000 patients, 58 developed local recurrence after median follow up of 67.3 months, and all recurrences were in-field or marginal. Probability heat map and equiprobability contours were generated to demonstrate the tumor extension probability. Based on proposed prediction model, CTV10% and CTV5% were defined to encompass corresponding subclinical disease. For 100 cases, mean DSC between predicted CTV and expert delineation were 0.89 ± 0.031 and 0.90 ± 0.020 for high-risk and low-risk CTV, indicating high similarity. Distances from GTV to predicted CTV were comparable to or slightly smaller than that to expert delineation in most directions. In multicenter evaluation, with assistance of predicted CTV, increased delineation accuracy was observed in all 5 oncologists, with mean DSC increased from 0.85 to 0.91 for high risk CTV and 0.87 to 0.93 for low risk CTV (P < 0.001 for 5 oncologists). Moreover, mean multi-observer DSC increased from 0.73 to 0.80 for high risk CTV, and 0.78 to 0.83 for low risk CTV (both P < 0.001) and average time spent on CTV delineation decreased from 30.3 to 14.9 min (P < 0.001). The probability-based predicted CTV was comparable to experienced expert delineation and might be enough for treating NPC. Predicted CTV significantly improved delineation accuracy in less experienced radiation oncologist and reduced inter-observer variance and time spent on CTV delineation.

Nonuniform Planning Target Volume Margins for Prostate Bed on the Basis of Surgical Clips on Daily Cone Beam Computed Tomography

PurposeWe hypothesized that the interfraction motions of the superior and inferior prostate beds differ and therefore require different margins. In this study, we used daily cone beam computed tomography (CBCT) to evaluate the motion of postprostatectomy surgical clips (separated to superior and inferior portions) within the planning target volume (PTV) to derive data-driven PTV margins. Methods and MaterialsOur study cohort included consecutive patients with identifiable surgical clips undergoing prostate bed irradiation with daily CBCT image guidance. We identified and contoured the clips within the PTV on the planning computed tomography and CBCT scans. All CBCT scans were registered to the planning computed tomography scan on the basis of pelvic bony structures. The superior border of the pubic symphysis was used to mark the division between the superior and inferior portions. ResultsEleven patients with 263 CBCT scans were included in the cohort. In the left–right direction, the global mean M, systematic error Σ, and residue error σ were 0.02, 0.03, and 0.16 cm, respectively, for superior clips, and 0.00, 0.03, and 0.03 cm, respectively, for inferior clips. In the anterior–posterior direction, the corresponding values were M = 0.01, Σ = 0.25, and σ= 0.37, respectively, for superior, and M = 0.08, Σ= 0.13, σ= 0.15, respectively, for inferior. In the superior–inferior direction, the values were M =-0.06, Σ= 0.23, and σ= 0.27, respectively, for superior, and M =-0.01, Σ= 0.21, σ= 0.20, respectively, for inferior. The results of the 2-tailed F tests showed that the anterior–posterior motion is statistically different between the superior and inferior portions in the anterior–posterior direction. There is no statistical difference in the superior–inferior and lateral directions. Therefore, we propose a set of nonuniform PTV margins (based on the formula 2.5 Σ+ 0.7σ) as 0.2 cm for all prostate beds in the left–right direction, 0.7 cm for all in superior–inferior, and 0.9 to 0.4 for superior–inferior in the anterior–posterior direction. ConclusionsThe difference in motion between the superior and inferior portions of the prostate bed is statistically insignificant in the left–right and superior–inferior directions, but statistically significant in the anterior–posterior direction, which warrants a nonuniform PTV margin scheme.

Periprosthetic bone quality affects the fixation of anatomic glenoids in total shoulder arthroplasty: in vitro study

Glenoid loosening, a common complication of shoulder arthroplasty, could relate to implant design and bone quality. However, the role of bone density has not been tested experimentally yet. In this study, tests on cadaveric specimens of varying bone density were performed to evaluate the effects of bone quality on loosening of typical anatomic glenoid implants. Cadaveric scapulae scanned with a quantitative computed tomography scanner to determine bone mineral density (BMD) were implanted with either pegged or keeled cemented glenoid components and tested under constant glenohumeral load while a humeral head component was moved cyclically in the inferior and superior directions. Implant superior and inferior edge lifting, defined as displacement from the underlying bone, was measured with linear variable differential transducers until we reached 23,000 test cycles, and statistical testing was performed for differences in edge lifting due to implant design and related to periprosthetic BMD. Edge lifting was statistically significant at all time points, but on average, implant design had no effect. Lifting was highest in specimens in which BMD below the lifting edge was lower, with trends of increased displacement with decreased BMD. Implant lifting was greater in glenoids of lower bone density for both implant designs. This finding suggests that fixation failure will most likely occur in bone of lower density and that the fixation design itself may play a secondary role.

Impact of a novel exponential weighted 4DCT reconstructionalgorithm.

PurposeThis work characterizes a novel exponential 4DCT reconstruction algorithm (EXPO), in phantom and patient, to determine its impact on image quality as compared to the standard cosine‐squared weighted 4DCT reconstruction.MethodsA motion platform translated objects in the superior–inferior (S‐I) direction at varied breathing rates (8–20 bpm) and couch pitches (0.06–0.1) to evaluate interplay between parameters. Ten‐phase 4DCTs were acquired and data were reconstructed with cosine squared and EXPO weighting. To quantify the magnitude of image blur, objects were translated in the anterior–posterior (A‐P) and S‐I directions for full‐width half maximum (FWHM) analysis between both 4DCT algorithms and a static case. 4DCT sinogram data for 10 patients were retrospectively reconstructed using both weighting factors. Image subtractions elucidated intensity and boundary differences. Subjective image quality grading (presence of image artifacts, noise, spatial resolution (i.e., lung/liver boundary sharpness), and overall image quality) was conducted yielding 200 evaluations.ResultsAfter taking static object size into account, the FWHM of EXPO reconstructions in the A‐P direction was 3.3 ± 1.7 mm (range: 0–4.9) as compared to cosine squared 9.8 ± 4.0 mm (range: 2.6–14.4). The FWHM of objects translated in the S‐I direction reconstructed with EXPO agreed better with the static FWHM than the cosine‐squared reconstructions. Slower breathing periods, faster couch pitches, and intermediate 4DCT phases had the largest reductions of blurring with EXPO. 18 of 60 comparisons of artifacts were improved with EXPO reconstruction, whereas no appreciable changes were observed in image quality scores. In 18 of 20 cases, EXPO provided sharper images although the reduced projections also increased baseline noise.ConclusionExponential weighted 4DCT offers potential for reducing image blur (i.e., improving image sharpness) in 4DCT with a tendency to reduce artifacts. Future work will involve evaluating the impact on treatment planning including delineation ability and dose calculation.