Skull Frame Research Articles

Two exceptionally preserved juvenile specimens of Gorgosaurus libratus (Tyrannosauridae, Albertosaurinae) provide new insight into the timing of ontogenetic changes in tyrannosaurids

ABSTRACT Known from dozens of specimens discovered since the early 20th century, Gorgosaurus libratus has arguably contributed more than any other taxon to our understanding of the life history of tyrannosaurids. However, juvenile material for this taxon is rare. Here, we describe two small, articulated Gorgosaurus specimens (skull lengths of ca. 500 mm) that help advance our knowledge of the anatomy and ontogeny of this taxon and of tyrannosaurids in general. The new specimens exhibit hallmark juvenile tyrannosaurid features, including long, low, and narrow skulls, large circular orbits, absent or incipient cranial ornamentation, ziphodont dentition, and an overall gracile skull frame. Comparison with other Gorgosaurus specimens of various ontogenetic stages allows for an examination of the timing of morphological changes that occurred through ontogeny in this taxon relative to other tyrannosaurids. Of particular note, Gorgosaurus and the larger Tyrannosaurus rex are found to have experienced similar ontogenetic transformations at similar percent skull length relative to the large known individuals for each respective taxon but at different absolute body sizes and biological ages, occurring at a larger size and older age in Tyrannosaurus than in Gorgosaurus. These results suggest a dissociation between the timing of cranial development and body size in tyrannosaurids. Finally, the recognition of ontogenetically invariant characters in Gorgosaurus makes it possible to determine the taxonomic identity of previously misidentified specimens.

A Practical 3D-Printed Model for Training of Endoscopic and Exoscopic Intracerebral Hematoma Surgery with a Tubular Retractor.

To present a three-dimensional (3D)-printed model that simulates endoscopic and exoscopic intracerebral hematoma (ICH) surgery with a tubular retractor. We used 3D printing technology to develop the model that consisted of the skull frame and a replaceable inserted module. Edible gelatin and animal blood were placed into the module to mimic brain tissue and the hematoma. Twenty neurosurgeons were recruited to participate in our training program that required the use of an endoscope and an exoscope to aspirate the hematoma with a tubular retractor. Five postgraduates were asked to complete the entire training with the endoscope five times. Questionnaires were distributed for feedback after the training program. The more experienced surgeons obviously performed better than the rather inexperienced surgeons, verifying that our model could reflect the ability of the trainees. As the training progressed, the scores of the postgraduates increased, and the average score of the fifth training was obviously higher than the first score. No significant differences were observed in the trainees' performance with the endoscope and the exoscope. The feedback questionnaires showed the average score for value of the simulator as a training tool was a 3.65 (on a 4-point scale). Our model received better comments regarding the bone texture (mean: 3.20), the brain tissue texture (mean: 3.20), and the experience in aspirating the hematoma (mean: 3.10). The surgical position (mean: 2.95), surgical approach (mean: 2.90), and simulated brain tissue (mean: 2.85) should be improved. Our model was practical for endoscopic and exoscopic ICH surgery training. The results of our program showed that prior surgical experience benefited the mastery of both the endoscopic and the exoscopic ICH surgery in the 3D-printed model. Our model could make mastering basic skills more efficient.

One-Day Two-Fraction Radiosurgery for Brain Metastases Using Gamma Knife.

Objective: We aimed to evaluate the feasibility of a one-day two-fraction Gamma Knife radiosurgery (GKRS) for brain metastases.Cases and methods: Ten cases with ten brain metastases (four cases of lung adenocarcinoma, one small cell lung carcinoma (SCLC), two renal cell carcinoma, one breast cancer, one esophageal carcinoma, and one bile duct carcinoma) were treated by one-day two-fraction (with an interval of more than six hours) GKRS under rigid skull frame fixation. Of the ten brain metastases, five lesions were in the frontal lobe, one in temporal, one in occipital, and three in the cerebellar hemisphere. The mean planning target volume (PTV) of the ten brain tumors was 7.8 ml (median, 8.0; range, 3.8 - 11.8). The ten targets of the mean prescription isodose volume (PIV) of 10.1 ml (median, 10.1; range, 4.4 - 15.9) were treated with a mean margin dose of 20.4 Gy (median, 20.5; range, 16.4 - 22) in two fractions. In five cases, other small brain metastases (one to seven tumors) were also treated simultaneously in a single fraction GKRS. The indication of two-fraction radiosurgery was large lesion size in eight, retreatment in three, the proximity of the motor area in three, and pre-existing perifocal edema symptom of dysarthria in two, nausea and vomiting in one, and dementia in one.Results: Eight cases were alive at the end of the follow-up period of one to nine months (median, 6). One patient with SCLC died four and a half months after GKRS, from aggressive regrowth of the treated frontal lesion after transient marked shrinkage. Another patient died four months after GKRS due to the progression of other brain tumors treated by single fraction GKRS at the same time. In nine of 10 cases, the size of the treated tumors was controlled until the end of the follow-up period or the patient’s death. In two cases, an additional GKRS was performed for newly developed brain metastases at distant locations at six months and five months after one-day two-fraction GKRS, respectively, and controlled at the end of the follow-up period.Conclusions: A relatively high dose may be safely delivered to large lesions, to those close to the important structures, or those with perifocal edema by one-day two-fraction radiosurgery. Local control was good except for a relapsed SCLC metastasis case. Evaluation in more cases with a longer follow-up period is necessary to determine definite indications and optimal prescription doses.

Distraction in cleft patient. where are we now?

Background: Distraction osteogenesis has two indications for the treatment of retruded midface and the alveolar cleft repair in patients with cleft lip and palate. CLP patients usually present with class III malocclusions and a narrow hard palate. Since 1997 DO has become an alternative option for treatment of maxillary hypoplasia in CLP patients. In most cases, the distractors used to induce maxillary distraction were placed externally, using a skull frame for stabilization in early period. It is easier to apply and can produce changes on the sagittal and vertical plane through external hooks by simply adjusting the force vectors.

A practical 3D printed simulator for endoscopic endonasal transsphenoidal surgery to improve basic operational skills.

We aimed to present a practical three-dimensional (3D) printed simulator to comprehensively and effectively accelerate the learning curve of endoscopic endonasal transsphenoidal surgery (EETS). The 3D printed simulator consists of three parts: (1) skull frame, (2) the nasal passage and the nasal alar of the face, and (3) a modified sella turcica. We aimed to improve three basic operational skills of surgeons: drilling, curetting, and aspirating. Eighteen neurosurgeons and five post-graduates were recruited and consented for the training. For trainees, (1) as the training progressed, the scores increased gradually, (2) a significant increase in the average scores was observed in the tenth training compared to the first training, and (3) there is a significant decrease in trainee variability in the shortening of the gap. The 18 neurosurgeons were divided into three groups: experts, assistants, and observers. For all three basic operations, (1) the average score of experts was obviously higher than that of the assistants, observers, and trainees' tenth training and (2) the average scores of assistants and observers were obviously higher than that of trainees' first training. A significant high in the average score between the assistants and the observers was seen for aspirating, but not for drilling or curetting. For curetting and aspirating, the tenth training average score of trainees was obviously higher than that of assistants and observers. This 3D printed simulator allows different endoscopic basic operations to be simulated and improves the EETS techniques of surgeons. We believed it to be a practical, simple, and low-cost simulator.

Examination of Whole Treatment Time Required for Multiple Metastatic Brain Tumors in Cobalt-60 Stereotactic Radiosurgery Procedures

A study was conducted to clarify the time required for each treatment procedure and whole treatment time from treatment records of 124 patients with metastatic brain tumors treated by Gamma Knife (GK) Perfexion during the period from June 2013 to November 2014. GK treatment procedure is as follows: a skull frame is attached to the patient's head, contrast-enhanced magnetic resonance (MR) imaging is acquired for treatment planning, the skull shape is provided by manual measurement, appropriate dose and dose distribution are determined for the target, irradiation is executed according to completed treatment plan, and the frame is removed after irradiation. As the results, it took 15.1±12.4 min for frame fixation, 30.1±11.5 min for MR scan, 5.0±1.0 min for skull measurement, 72.5±42.4 min for treatment planning, 91.3±56.1 min for irradiation, 99.2±60.6 min as treatment time, and 5.6±5.1 min for frame removal. In conclusion, it was shown that GK Perfexion stereotactic radiosurgery has high treatment efficiency and less burden on patients.

Validation and analysis of dose distributions in a new and entirely redesigned cobalt-60 stereotactic radiosurgery units.

The objective of this study was to evaluate the reproducibility of dose distributions in stereotactic treatment planning throughout Gamma Knife (GK) stereotactic radiosurgery (SRS) procedures in both GK model C and Perfexion (PFX). An originally-developed phantom and a radiochromic film were used for obtaining actual dose distributions. The phantom, with inserted films, was placed on a Leksell skull frame. Computed tomography (CT) was then acquired with a stereotactic localizer box attached to the frame, dose planning was made using the Leksell GammaPlan treatment planning system, and the phantom was ended up as beam delivery on an equal with clinical radiosurgery process. The reproducibility of the dose plan was provided by distance to agreement (DTA) values between planned and irradiated dose distributions calculated by dedicated film analysis software. The DTA values were determined for the isodose lines at 30%, 50%, 70%, and 90% of the maximum dose. In our study, the reproducibility of dose distributions in GK PFX was lower than in GK model C. As the results common to both units, the mean values of middle dose area (50% isodose) were about half the values of high (90% isodose) and low (30% isodose) dose area. Therefore validation of dose distributions is absolutely essential in commissioning of GK PFX. In addition, when risk organs are close to the target, dose prescription should be normalized for middle isodose line.

Effective usage of a clearance check to avoid a collision in Gamma Knife Perfexion radiosurgery with the Leksell skull frame.

Skull frame attachment is one of the most significant issues with Gamma Knife radiosurgery. Because of the potential for suffering by patients, careful control of the frame position is required to avoid circumstances such as collision between the frame or the patient's head and the collimator helmet, and inaccessible target coordinates. This study sought to develop a simulation method to find the appropriate frame location on the patient's head by retrospective analysis of treatment plans for brain metastasis cases. To validate the accuracy of the collision warning, we compared the collision distance calculated using Leksell GammaPlan (LGP) with actual measured distances. We then investigated isocenter coordinates in near-collision cases using data from 844 previously treated patients and created a clearance map by superimposing them on CT images for just the frame, post and stereotactic fiducial box. The differences in distance between the simulation in LGP and the measured values were <1.0 mm. In 177 patients, 213 lesions and 461 isocenters, there was a warning of one possible collision. The clearance map was helpful for simulating appropriate skull frame placement. The clearance simulation eliminates the psychological stress associated with potential collisions, and enables more comfortable treatment for the patient.

Effect of skull contours on dose calculations in Gamma Knife Perfexion stereotactic radiosurgery

In treatment planning of Leksell Gamma Knife (LGK) radiosurgery, the skull geometry defined by generally dedicated scalar measurement has a crucial effect on dose calculation. The LGK Perfexion (PFX) unit is equipped with a cone‐shaped collimator divided into eight sectors, and its configuration is entirely different from previous model C. Beam delivery on the PFX is made by a combination of eight sectors, but it is also mechanically available from one sector with the remaining seven blocked. Hence the treatment time using one sector is more likely to be affected by discrepancies in the skull shape than that of all sectors. In addition, the latest version (Ver. 10.1.1) of the treatment planning system Leksell GammaPlan (LGP) includes a new function to directly generate head surface contouring from computed tomography (CT) images in conjunction with the Leksell skull frame. This paper evaluates change of treatment time induced by different skull models. A simple simulation using a uniform skull radius of 80 mm and anthropomorphic phantom was implemented in LGP to find the trend between dose and skull measuring error. To evaluate the clinical effect, we performed an interobserver comparison of ruler measurement for 41 patients, and compared instrumental and CT‐based contours for 23 patients. In the phantom simulation, treatment time errors were less than 2% when the difference was within 3 mm. In the clinical cases, the variability of treatment time induced by the differences in interobserver measurements was less than 0. 91%, on average. Additionally the difference between measured and CT‐based contours was good, with a difference of −0.16%±0.66% (mean ±1 standard deviation) on average and a maximum of 3.4%. Although the skull model created from CT images reduced the dosimetric uncertainty caused by different measurers, these results showed that even manual skull measurement could reproduce the skull shape close to that of a patient's head within an acceptable range.PACS number: 87.53.Ly

Useful base plate to support the head during Leksell skull frame placement in gamma knife perfexion radiosurgery.

We developed an original base plate to support both the patient's head and a Leksell stereotactic skull frame during frame placement in the supine position. The base plate is made of transparent acrylic board with holes at the posterior posts for injection of local anesthetics and maneuver of fixation screws through them. A stable and comfortable position of the patient's head in a supine position is obtained and maintained on this base plate with an air-pressure cuff beneath the patient's head. The patient is able to keep a stable, relaxed and comfortable posture during the procedures of skull frame placement.

Optimal conditions for multifocal VEP recording for normal Japanese population established by receiver operating characteristic analysis

The purpose of this study was to establish optimal conditions for recording multifocal visual evoked potentials (mVEPs) in Japanese individuals, whose skull frame presumably differs from Caucasians. The scalp point that was extended from the calcarine fissure was identified using magnetic resonance imaging scans of 200 subjects. MVEPs were recorded from 56 individuals using three single channels and combinations of vertical and horizontal channels. Five electrodes were placed at the inion, 4cm above the inion, 2.5cm below the inion, 4cm to the left or 4cm to the right of the inion. The signal-to-noise ratio (SNR) was obtained by measuring the root-mean-square (RMS) amplitude of a signal window (45-150ms) from each of 60-local responses that was divided by the average of the 60 RMS amplitudes of the noise window (325-430ms). Receiver operating characteristic (ROC) analyses were performed based on the proportion of mVEP responses that exceeded a specific SNR criterion, calculated for both the signal window and the noise window. The position of the calcarine fissure relative to the inion was significantly lower than the value reported for Caucasians. The ROC analyses disclosed that bi-channel combinations (one vertical and one horizontal) had significantly better performance to discriminate signal from noise in 60-local mVEP responses compared to any single channel and performed similarly to the tri-channel combination. Two sets of perpendicular channels should be simultaneously used in recording mVEP responses from Japanese people, among whom skull frame characteristics differ from those observed in Caucasians.

Stereotactic Imaging for Radiosurgery: Localization Accuracy of Magnetic Resonance Imaging and Positron Emission Tomography Compared with Computed Tomography

Computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) provide complementary information for treatment planning in stereotactic radiosurgery. We evaluated the localization accuracy of MRI and PET compared with CT. Two kinds of phantoms applicable to the Leksell G stereotactic skull frame (Elekta, Tokyo) were developed. Deviations of measured coordinates at target points (x = 50, 100, 150; y = 50, 100, 150) were determined on different axial planes (z = 30–140 for MRI and CT study and Z = 50–120 for PET and CT study). For MRI, the deviations were no more than 0.8 mm in each direction. For PET, the deviations were no more than 2.7 mm. For both imaging modalities studied, accuracy was at or below the imaging resolution (pixel size) and should be considered useful for clinical stereotactic planning purposes.

Stereotaxic brain surgery. II. Description of a method using biplane television guidance.

We have described a new method of probe-target alignment in stereotaxic brain surgery. Using a biplane television (TV) camera-monitor system with mirrors to bring the TV optical axis in coincidence with the parallel x-ray central beam, it is possible to project on the TV monitor (using visual light photons) the exact same attitude of the skull and stereotaxic frame seen by the radiographic film (using x-ray photons). The TV monitor displays the probe-guide and head of the patient but not the target (we are not using fluorscopy). The standard x-ray film displays the target and projected probe-target line. Now the x-ray film image is physically superimposed upon the optical TV monitor image in the frontal and lateral planes.