Use of the Brown-Roberts-Wells stereotactic frame for functional neurosurgery

The Brown-Roberts-Wells (BRW) stereotactic unit has proven itself to be a highly accurate instrument for biopsying or locating pathologic intracranial lesions based on CT scan information. We utilized the BRW frame to select 18 target sites in 12 patients undergoing functional stereotactic procedures. Two patients had bilateral cingulumotomies, 5 had thalamotomies for movement disorders, and 5 underwent electrode implantations for the treatment of chronic pain. Stereotactic frame settings were determined using a positive contrast ventriculogram, orthogonal radiographs, and a computer program provided with the BRW system. In addition, attempts were made to select targets based on CT scan landmarks alone, and these were compared to those derived using ventriculography. We found the BRW frame to be a satisfactory device for performing functional neurosurgical procedures based on ventriculographic landmarks. Coordinates derived from CT scans were similar to those obtained with ventriculography, but were not accurate enough to permit the use of CT scanning as the sole means of target identification. Although future improvements in imaging techniques and computer software are likely to occur, our experience supports ventriculography as the current method of choice for the precise localization of functional targets with the BRW stereotactic system.     

Single-scan stereotactic tumor biopsy and brachytherapy

Stereotactic tumor biopsy and brachytherapy catheter implantation can be accomplished with targets derived from computed axial tomography and magnetic resonance scans. Computer manipulation of image data allows both diagnostic and therapeutic procedures to be carried out from a single set of scan slices. This eliminates the need for repeat scanning as part of the surgical procedure. Microcomputer technology is sufficiently advanced to handle the images and graphics necessary for stereotactic neurosurgery. A system based on the IBM PC/AT designed for this purpose uses readily available graphics software and custom-designed imaging programs. Direct loading of computed axial or magnetic resonance scan images from magnetic tape can be accomplished. Determination of points, contours and volumes in three-dimensional space allows intraoperative alignment of image data and patient landmarks within the stereotactic head frame using pattern recognition overlays. Three-axis scaling for magnification correction along with rotational and linear data transformations provide the basis for single-scan stereotaxis. Interactive computer graphics integrate image, patient and frame coordinates for target determination. This method eliminates the need to design and fabricate nonmagnetic or radiolucent scanner-compatible devices.     

Stereotactic neurosurgery and computerized tomographic scanning

The marriage of computerized tomographic (CT) scanning and stereotactic surgery opens up new technical possibilities, as it becomes feasible to introduce a probe into any lesion which is identified on a CT scan. The various CT stereotactic techniques are reviewed, and generally involve four variations. The head holder of a standard stereotactic apparatus can be adapted to the CT scanner to interdigitate the coordinates of both devices in a known relationship. Second, some types of CT scanners allow the visualization of the vertical coordinate. Third, a stereotactic microdrive can be incorporated into the scanner. Finally, a simple aiming device can be attached to the patient's head and repeated scans taken as the probe is advanced to the target. Various authors have reported the use of techniques for biopsy, aspiration of cysts or hematomas, insertion of radioisotopes, or as an adjunct to open surgery.     

Computer tomography-controlled stereotactic surgery

In computed tomography (CT)-controlled stereotactic surgery, the coordinate system of the CT scanner is applied to determine the target depth and direction as well as for readjustment of final probe direction. This method can be used for all types of stereotactic surgery for the brain.     

Physical aspects of dynamic stereotactic radiosurgery

Dynamic stereotactic radiosurgery is a radiosurgical technique based on a medium-energy isocentric linear accelerator and a stereotactic frame. The technique uses concurrent and continuous rotations of both the gantry (300 degrees, from 30 to 330 degrees) and the couch (150 degrees, from 75 to -75 degrees). It gives a uniform dose (+/- 5%) within the target volume and dose fall-offs outside the target volume comparable to those obtained from presently known radiosurgical techniques.     

Magnetic resonance imaging stereotaxy: recognition and utilization of the commissures

Magnetic Resonance Imaging (MRI) offers a non-invasive method to visualize the intracerebral structures. Coupled to a compatible stereotactic frame and software, MRI can be used to determine the coordinates of intracranial targets. Coordinates of the anterior commissure, posterior commissure, targets and intercommissural distance were obtained from positive contrast ventriculography and by MRI in 6 patients undergoing stereotactic localization prior to the implantation of stimulating thalamic electrodes for pain control. The correlation of coordinates and measurements obtained with ventriculography and MRI is +/- 1 mm in most measurements, but up to 3 mm in 2 cases. Magnetic resonance stereotaxy allows non-invasive and precise localization of intracerebral targets, but does not yet allow its routine use with confidence. Further understanding of distortion and artifacts and corrections of these is mandatory.     

Stereotactic surgery in the rhesus monkey (Macaca mulatta) utilizing intracerebral landmarks

A stereotactic method utilizing an intracerebral coordinate system and ventricular radiography was developed and applied in rhesus monkeys. The intercommissural line (CA-CP) and two perpendiculars to this line served as the main references for th coordinate system. Surgical placements with the use of this technique were made in various deep cerebral and cerebellar nuclei in 12 Macaca mulatta and the accuracy of the surgery was evaluated histologically. In 11 of the 12 monkeys, the intended targets were achieved precisely. The advantages and pitfalls of the proposed method are discussed.     

The role of computed tomographic and digital radiographic techniques in stereotactic procedures for electrode implantation and mapping, and lesion localization

This paper describes a computer-based system for analyzing stereotactic CT scans and angiograms. Simple Plexiglas frames containing metallic marker pellets and rods are affixed to the sides of the frame during CT scanning and angiography. The images of these markers are recognized by the computer program and used to compute the frame coordinate system. Coordinates of a lesion on CT and angiogram images may be readily computed and coordinate sets specified by the operator may be displayed on the imager, along with positions of implanted electrodes and a numerical indication of recorded activity for each site.     

Simple gene silencing using the trans‐acting siRNA pathway

In plants, particular micro‐RNAs (miRNAs) induce the production of a class of small interfering RNAs (siRNA) called trans‐acting siRNA (ta‐siRNA) that lead to gene silencing. A single miRNA target is sufficient for the production of ta‐siRNAs, which target can be incorporated into a vector to induce the production of siRNAs, and ultimately gene silencing. The term miRNA‐induced gene silencing (MIGS) has been used to describe such vector systems in Arabidopsis. Several ta‐siRNA loci have been identified in soybean, but, prior to this work, few of the inducing miRNAs have been experimentally validated, much less used to silence genes. Nine ta‐siRNA loci and their respective miRNA targets were identified, and the abundance of the inducing miRNAs varies dramatically in different tissues. The miRNA targets were experimentally verified by silencing a transgenic GFP gene and two endogenous genes in hairy roots and transgenic plants. Small RNAs were produced in patterns consistent with the utilization of the ta‐siRNA pathway. A side‐by‐side experiment demonstrated that MIGS is as effective at inducing gene silencing as traditional hairpin vectors in soybean hairy roots. Soybean plants transformed with MIGS vectors produced siRNAs and silencing was observed in the T1 generation. These results complement previous reports in Arabidopsis by demonstrating that MIGS is an efficient way to produce siRNAs and induce gene silencing in other species, as shown with soybean. The miRNA targets identified here are simple to incorporate into silencing vectors and offer an effective and efficient alternative to other gene silencing strategies.     

Positioning accuracy of a single-isocenter multiple targets SRS treatment: A comparison between Varian TrueBeam CBCT and Brainlab ExacTrac

PurposeThis study compared the positioning accuracy between cone-beam CT (CBCT) and ExacTrac (ETX) for a single-isocenter multiple target stereotactic radiosurgery (SRS) on two TrueBeam STx systems.MethodsA single-isocenter treatment plan was simulated on an anthropomorphic head phantom with six spherical steel ball bearings (BBs). One of the BBs was chosen to be the isocenter. The five off-isocenter targets were located at various distances from the isocenter. MV portal images were generated to evaluate the deviations between the expected and the real center of the targets after CBCT and ETX positioning, respectively.ResultsThe evaluation of the positioning accuracy for the isocenter target showed that CBCT and ETX positioning provided comparable, sub-millimetric results. Deviations in positioning accuracy were also calculated for all other targets, also showing comparable results for CBCT and ETX. Moreover, our study showed that the deviation between CBCT and ETX positioning were in better agreement for TBSTx1 and deviated slightly higher on TBSTx2 (maximum: 1.23 mm at S/I direction), due to a less perfect alignment between the CBCT coordinate system and the ETX coordinate system on TBSTx2 compared to TBSTx1. This study also showed a correlation between the target positioning accuracy and the distance to the isocenter.ConclusionThe positioning accuracy of ETX and CBCT for targets located at isocenter and off-isocenter locations was compared on two treatment machines and found comparable. Our study highlights the importance of a proper calibration procedure, to ensure correct alignment between the CBCT, ETX and machine coordinate systems.     

Experience using two CT-guided stereotactic biopsy methods

15 patients had intracranial CT-guided stereotactic biopsies. Biopsies were performed either with a Riechert-Mundinger stereotactic frame modified for use in the CT or by using the CT scan to establish the relationship of the intracranial lesion to identifiable bony landmarks, and subsequently performing the biopsy in a standard stereotactic frame. Both systems provided safe and accurate methods for obtaining intracranial tissue.     

MRI contribution to the stereotactic management of cerebral tumours

Of 67 patients with cerebral tumours studied by MRI, 60 underwent stereotactic biopsy for histological diagnosis. The data from MRI were compared with those obtained from the CT scan with regard to the pathological diagnosis. The tumoural nature and extent of a lesion were better revealed by MRI. The single or multiple localization of the process was also seen better by MRI. Moreover, the sagittal-plane views shown by MRI provide much more accurate target placement and probe guiding for an orthogonal stereotactic approach. Finally, a post-biopsy MRI can show the biopsy site in relation to the tumour better.     

Animal research stereotactic instrument modified for computed tomographic guidance

While target localization for human stereotactic surgery has been refined by computed tomographic (CT) and magnetic resonance imaging (MRI), stereotaxis in experimental animals has remained dependent upon external cranial landmarks and standardized atlas coordinates. To overcome the limitations and inaccuracies of animal devices using the original Horsley-Clarke method, we modified a standard animal stereotactic instrument in order to make target localization and coordinate determination possible with CT imaging. Although the device can be adapted to any medium-sized animal species, we demonstrate its use with dogs here.     

A Flexible Calibration Method Using the Planar Target with a Square Pattern for Line Structured Light Vision System

A flexible calibration approach for line structured light vision system is proposed in this paper. Firstly a camera model is established by transforming the points from the 2D image plane to the world coordinate frame, and the intrinsic parameters of camera can be obtained accurately. Then a novel calibration method for structured light projector is presented by moving a planar target with a square pattern randomly, and the method mainly involves three steps: first, a simple linear model is proposed, by which the plane equation of the target at any orientations can be determined based on the square’s geometry information; second, the pixel coordinates of the light stripe center on the target images are extracted as the control points; finally, the points are projected into the camera coordinate frame with the help of the intrinsic parameters and the plane equations of the target, and the structured light plane can be determined by fitting these three-dimensional points. The experimental data show that the method has good repeatability and accuracy.     

Assessment of intra-fraction motion during automated linac-based SRS treatment delivery with an open face mask system

Purpose/objectiveTo evaluate intra-fraction target shift during automated mono-isocentric linac-based stereotactic radiosurgery with open-face mask system and optical real-time tracking.Materials/methodsNinety-five patients were treated using automated linac-based stereotactic radiosurgery in 1–5 fractions with single isocenter for a total of 195 fractions. During treatment, patient positioning was tracked real-time with optical surface guidance and immobilized with a rigid open-face mask. Patients were re-positioned if optical surface guidance error exceeded 1 mm magnitude or 1°. Translational and rotational intra-fractional changes were determined by post-treatment CBCT matched to the planning CT. Target specific error was calculated by translation and rotation matrices applied to isocenter and target spatial coordinates.ResultsFor 132 fractions with isocenter within a single target, the median shift magnitude was 0.40 mm with a maximum shift of 1.17 mm. A total of 398 targets treated for plans having multiple or single targets that lied outside isocenter, resulted in a median shift magnitude of 0.46 mm, with median translational shifts of 0.20 mm and 0.20° rotational shifts. A 1 mm PTV margin was insufficient in 18% of targets at a distance greater than 6 cm away from isocenter, but sufficient for 96% of targets within 6 cm.ConclusionsThe findings of this study support 1 mm PTV expansion due to intra-fraction motion to ensure target coverage for plans with isocenter placement less than 6 cm away from the targets.     

Accuracy of the analysis of multiple small fragments of glial tumors obtained by stereotactic biopsy.

To examine the reliability of the diagnoses reached on multiple small fragments of cerebral glial tumors obtained via stereotactic biopsy, samples obtained from 100 consecutive glial tumors (during real or simulated biopsy) were studied by cytology and histology. In comparison to the definitive diagnosis made on the whole tumor, a correct positive diagnosis on the biopsy sample was made by histology in 96% of cases and by cytology in 93% of the cases (with 96% correct results when combining both methods). A correct identification of the tumor type and grade was achieved by histology in 82% of cases and by cytology in 80% of the cases (with 85% correct results when combining both methods). The limits of stereotactic biopsy are related to the difficulty of identifying all of the typical tumor features on tiny tissue fragments of a pleomorphic neoplasm, such as a glioma. This study demonstrates that better results may be obtained by using both cytology and histology to study multiple stereotactic biopsy samples from glial tumors.     

An applicability study on a CT-guided stereotactic technique for functional neurosurgery

When a CT-guided stereotactic technique for functional neurosurgery is adopted, extremely precise targeting is needed to obtain satisfactory surgical results. In this study the authors have investigated the accuracy of the target points determined by CT-guided techniques and compared with those of conventional roentgenographically controlled stereotactic procedures. Stereotactic surgery, employing the Brown-Roberts-Wells (BRW) system, was performed contemporarily 26 times in 23 patients, that is, 9 times in 8 patients for functional neurosurgery using with the roentgenographic method, and 17 times in 15 patients with the CT-guided method only for intracranial neoplasm biopsy. As a result, there were no problems of accuracy of determining the target points by CT-guided stereotactic surgery with the BRW system. When applying this technique for functional neurosurgery, it should be pointed out that there could be a discrepancy within 2 mm from the conventional target determination.     

A multipurpose CT-guided stereotactic instrument of simple design

The instrument is based upon a radiolucent ring fixed to the skull by four pins. This locks into a frame for CT scanning from which the x, y and z stereotactic coordinates are derived. The head ring may be locked into a compatible support on the operating table for biopsy. A similar support and localization system is used for rotational radiotherapy. With the current 14 MeV apparatus, fields as small as 2 cm in diameter are available with 90% dosage fall-off in the surrounding 1-cm shell.     

Computer-assisted stereotactic biopsy of intracranial lesions

The use of a computer program that allows the integration of stereotactically gathered CT, MRI and digital angiographic data in the planning of a biopsy trajectory is described. This system has been used to perform 447 stereotactic biopsies in 439 patients. Intracranial hemorrhages occurred in three patients; combined morbidity and mortality was less than 1%. Incorporation of angiographic data and visualization of the surgical trajectory enhances the safety and accuracy of stereotactic biopsy of intracranial lesions.     

Three-dimensional stereotactic anatomy of the human trigeminal nerve nuclear complex

The trigeminal nuclear complex and its spinal tract extend throughout the greater part of the brain-stem and at medullary levels form the target site for producing stereotactic lesions. This paper describes a method for three-dimensional drawings of this nuclear complex. A stereotactic atlas of the human brain-stem and cerebellar nuclei has formed the data base. The two-dimensional composite transverse sections, at 1-mm intervals have been digitized using an X-Y coordinate plotting microscope. Computer programs have been written to generate drawings of a single transverse hemisection as well as regeneration of the opposite hemibrain-stem section. Specific programs were used to reconstruct serial transverse section outlines and incorporate the trigeminal nuclear complex with and without hidden line removal techniques and colour graphic display facilities. Rotation about the x, y and z axes was possible and permits any view of the reconstructed specimen to be computer-generated. A further program for reconstructing structures as stereopairs is presented.