Stereotactic Localization Research Articles

Perioperative Technical Complications in Deep Brain Stimulation Surgeries.

Deep brain stimulation (DBS) surgeries are multi-faceted and the various steps are interconnected. Since its first implementation, the method of DBS surgery has undergone changes. We have encountered several expected and also non-expected perioperative technical complications in the past seventeen years. Here, we describe the stereotactic frame, stereotactic localizer and planning station related complications and how we have managed them as much as possible. This study is a retrospective qualitative analysis of the documented technical events encountered during DBS surgeries from 1999 onwards. We have collected these events from a cohort of approximately 921 DBS electrodes implantations from the centers of the authors. Stereotactic frame related complications included movement related fixation problems, head anatomy related problems, and lack of maintenance related issues. Localizer related complications were compatibility issues of the stereotactic localizer and planning station, field of view effect on fiducials, air bubbles in localizers using liquid solutions, and disengaged localizer effect. Planning station related complications included image fusion failures and cerebrospinal fluid signal effect on image fusion. The road to success in DBS therapy passes through the ability to cope with surgical and technical complications. Each step is unconditionally connected to the other, and detection of the problems that can be encountered in advance and preparations for these negative conditions are the key to success for the group responsible for executing the therapy. We are still learning from these events and advance our surgical approaches.

One Lung, Two Coronary Stents and Three Centimeters Malignant Brain Tumour! Tailored Anaesthesia for a Lethal Combination

When patient-related concerns are multiple, the anesthetic considerations also multiply. Stereotactic neurosurgery is done for diagnostic and/or therapeutic purposes for selective brain lesions and may require prolonged general anesthesia. It involves three-dimensional localization of lesions (for biopsy/treatment) utilizing a specialized stereotactic localization head frame system. Airway management (both mask ventilation and endotracheal intubation) becomes difficult with the frame in situ. We hereby present a known hypertensive patient with raised intracranial tension for stereotactic neurosurgery. Our patient also had two coronary artery stents, following previous myocardial ischemia. A major anesthetic challenge was posed by the presence only one lung in this patient, following a left-sided pneumonectomy done for bronchogenic carcinoma. This case report highlights the successful anesthetic management of such a complex case with judicious ventilatory and hemodynamic optimization.

157P - Accuracy and adequacy of pre-operative bracketing for therapeutic excision of non-palpable malignant breast lesions

Bracketing comprises of using two or more needles for localization of boundaries of an impalpable breast lesion. The tissue around the wires is excised and sent for histopathology. Objectives: To determine the accuracy & adequacy of pre-operative bracketing for therapeutic excision of non-palpable malignant breast lesions and in achieving tumor free margins. Retrospective review of mammograms & pathology reports of patients who underwent bracketing for malignant breast lesions at AKUH from January 2004 to April 2016. All cases of clinically non-palpable primary malignant breast lesions requiring therapeutic excision and with complete clinical response to Neoadjuvant therapy targeted for breast conservation were included whereas those with benign pathology were excluded. 76 patients with mean age of 48.09 years (range 25 - 81 years) underwent bracketing for excision of both benign and malignant breast lesions. 62 patients underwent breast conservation surgery for a pre-operative diagnosis of IDC (n = 56), ILC (n = 3), DCIS (n = 2) and metaplastic carcinoma (n = 1) with the help of bracketing. 85.5% (n = 53) received neo-adjuvant chemotherapy to reduce the size of lump. 93.5% (n = 58) underwent stereotactic wire localization, 4.8% (n = 3) underwent sonographic localization whereas 1.6% (n = 1) was localized with the help of both mammogram and ultrasound. Presence of radiopaque marker within the excised specimen and grossly adequate margins around the lesion guided the surgeon to decide about further margin excision. 95.2% (n = 59) had negative margins of the breast lump and 2 out of 62 patients (3.2%) had close margins (DCIS at 0.1cm from closest margin). 1.6% (n = 1) patient had invasive tumor at the margin. None of the re-excised tissue in 2 patients with close margins showed any evidence of tumor in the final histopathology report except the patient with positive margin who underwent second procedure of margin excision followed by mastectomy Our study showed that bracketing wire localization is a beneficial procedure in terms of achieving clear histologic margins in breast conservation surgery without significant increase in the rate of re-excision

EP 9. GPi Deep Brain Stimulation for the treatment of status distonicus in tardive dystonia

Introduction Dystonia is a movement disorder due to sustained muscle contractions that cause twisting and repetitive movements conditioning abnormal postures. Tardive dystonia generally follows long treatment with neuroleptics. An extreme condition called status distonicus may even be life threatening, determining spasm of axial musculature leading to respiratory or cardiac arrest. Bilateral pallidotomy provided significant benefit to dystonic symptoms in some patients; moreover, in recent years, pallidotomy has been replaced from pallidal DBS; pallidal DBS is particularly effective both in primitive generalized dystonia and in tardive dystonia consequent to neuroleptics. Objectives To report DBS for the treatment of severe iatrogenic dystonia refractory to medical treatment. Patient and methods A 19 years-old boy affected by severe behavior disorder was treated with neuroleptic drugs (haloperidole). After three years of treatment, appeared severe neck and axial dystonia with initial involvement of the extremities. The change in the pharmacological treatment led to an initial improvement, followed by a progressive and relentless worsening and loss of motor autonomy. The patient also experimented severe dysphagia and several episodes of ab-ingestis pneumonia. Anticholinergic and dopaminergic treatment failed to improve symptoms. The patient progressively felt in a generalized status distonicus. At admission, F-M DRS was 74. For this potentially threatening for life condition, he was candidated for bilateral GPi DBS. After stereotactic localization of ventro-mesial-posterior part of Gpi on volumetric isotropic T1 MRi coupled with Shaltenbrandt & Wahren atlas, bilateral DBS was performed in general sedation, with intraoperative neurophysiology. A couple of quadripolar electrodes were inserted and immediately connected with IPG (Activa RC Medtronic). Results Stimulation started during postoperative day 2. After initial adjustment of the stimulation parameters we appreciated a clear reduction in the intensity and frequency of dystonic spasms, without surgical complication or adverse effects. At discharge the patient was able to walk without help, no dysphagia has been complained for and dystonic spasms were absent. Stimulation parameters were settled as following: left GPi 1- case positive, 2.0 V, 210 μs, 130 Hz; right GPi 9-case positive, 2.0 V, 210 μs, 130 Hz. At one year follow-up F-M DRS is 20. Conclusion The role of DBS in secondary dystonia is still debated because of several failures; important factors in the surgical outcome are: the etiology of dystonia, the absence of skeletal deformity, younger age at surgery and shorter duration of disease. Another topic is the time of early efficacy of DBS, very varying among different reports, but generally considered in the span of weeks or months. Tardive dystonia, due to neuroleptic therapy, seems to be affected from DBS, better than other secondary forms. GPi DBS has also been described to be effective in the treatment of status distonicus and it is considered the treatment of choice in the acute management of this life-threatening condition. In this case we found a striking improvement in F-M DRS, since the first days, with prompt resolution of status distonicus. We suggest the indication to acute treatment with DBS in case of status distonicus in course of tardive dystonia.

EP 79. Comparative study of microrecording-based STN location and MRI-based STN location

Question STN-DBS could be improved by specifically targeting the dorsolateral part of the STN. However, the correspondence between the location of the STN on T2 MRI images used for targeting and the location of the neurophysiological STN remains unclear. In this study, we compared the STN borders on T2 MRI images with the STN borders identified by microelectrode recordings (MER), measured during DBS surgery. We study the differences between MER-based STN and MRI-based STN in 1.5 T, 3.0 T and 7.0 T images. Methods An atlas-based 3D model of the STN was automatically fitted onto the exact stereotactic locations of the MER points using their classifications as inside or outside the STN. The agreement between STN models and the MRI images of the STN was evaluated by an experienced neurosurgeon. T2 MRI images of 1.5 T (n = 14), 3.0 T (n = 10) and 7.0 T (n = 8) scans were compared. Results The dorsal border of the STN was identified more dorsal on the MRI than it was by MER. This was significant in the 3.0 T and 7.0 T images, with similar mismatch patterns decreasing towards the medial side of the dorsal border ( Fig. 1 ). The lateral border was identified significantly more medial on the MRI than it was by MER, for both 1.5 T and 3.0 T images. The STN borders on 7.0 T images showed no significant differences with MER ( Fig. 2 ). Conclusions MER helps to refine the delineation of the dorsal and lateral border of the STN in MRI-based targeting. Increasing MRI field strength to 7.0 T may improve identification of the lateral, but not the dorsal STN border.

Stereotactic modulation of blood-brain barrier permeability to enhance drug delivery.

Drug delivery in the CNS is limited by endothelial tight junctions forming the impermeable blood-brain barrier. The development of new treatment paradigms has previously been hampered by the restrictiveness of the blood-brain barrier to systemically administered therapeutics. With recent advances in stereotactic localization and noninvasive imaging, we have honed the ability to modulate, ablate, and rewire millimetric brain structures to precisely permeate the impregnable barrier. The wide range of focused radiations offers endless possibilities to disrupt endothelial permeability with different patterns and intensity following 3-dimensional coordinates offering a new world of possibilities to access the CNS, as well as to target therapies. We propose a review of the current state of knowledge in targeted drug delivery using noninvasive image-guided approaches. To this end, we focus on strategies currently used in clinics or in clinical trials such as targeted radiotherapy and magnetic resonance guided focused ultrasound, but also on more experimental approaches such as magnetically heated nanoparticles, electric fields, and lasers, techniques which demonstrated remarkable results both in vitro and in vivo. We envision that biodistribution and efficacy of systemically administered drugs will be enhanced with further developments of these promising strategies. Besides therapeutic applications, stereotactic platforms can be highly valuable in clinical applications for interventional strategies that can improve the targetability and efficacy of drugs and macromolecules. It is our hope that by showcasing and reviewing the current state of this field, we can lay the groundwork to guide future research in this realm.

Stereotactic Localization of the Monro Foramen and the Safest Stereotactic Interforniceal Approach to the Third Ventricle: A Neuroanatomical Study.

To localize the human foramen of Monro stereotactically, to define the anatomical parameters of the safest stereotactic transcallosal transseptal interforniceal approach to the third ventricle, and to show how neurosurgeons could use them in preoperative planning. Our material consisted of 44 formalin-fixated human cerebral hemispheres. We found the location of the anterior (AC) and posterior commissure at the internal hemispheric surface. The posterosuperior border of the AC (point A) was our stereotactic reference point with coordinates (X, Y, Z) = (0, 0, 0). We found the Monro foramen location and measured the stereotactic coordinates of its anterior inferior border (point B). The safest trajectory to the third ventricle has to pass as far as possible from points A and B so as not to traumatize the choroid plexus of the Monro foramina or the AC. The midpoint of the AB distance (point M) is the stereotactic point that provides this safest trajectory. We also measured AB length and point M stereotactic coordinates. Mean stereotactic coordinates of the (midline projection of the) point B were (X, Y, Z) = (0, -0.6, 2.4). Point B was located averagely 3.2 mm far from point A. Mean stereotactic coordinates of the point M, a necessary component of the trajectory of the safest stereotactic interforniceal approach to the third ventricle, were (X, Y, Z) = (0, -0.3, 1.2). Point M was located 1.6 mm far from point A. The present study shows how neurosurgeons can localize and use crucial anatomical landmarks, namely the AC and foramen of Monro, to approach the third ventricle safely via a stereotactic interforniceal technique. This can be achieved during preoperative planning with simple identification of stereotactic points A, B, and M on preoperative median sagittal magnetic resonance images.

Stereotactic anatomical localization in complex sinus surgery: A systematic review and meta-analysis.

It is recognized that stereotactic anatomical localization (SAL) is a useful tool in endoscopic sinus surgery (ESS), but it may be most beneficial for complex rather than routine sinus procedures. This review sought to determine the safety and efficacy of SAL in complex indications for ESS. PubMed, EMBASE, Centre for Reviews and Dissemination, and the Cochrane Library were searched from inception up to April 4, 2014. English studies comparing ESS with and without SAL in complex cases were included. Complex surgery included revision surgery, inverted papilloma, extensive sinus disease, or biopsy of tumors that are not exophytic. Safety outcomes included total, major, minor, orbital, dural, and major hemorrhage complications. Efficacy outcomes included operation completion, revision surgery, and patient-reported outcomes. Meta-analysis generated fixed-effects Mantel-Haenszel odds ratios (OR) and confidence intervals (CI). A total of 2,381 studies were identified, of which nine met the inclusion criteria. Meta-analyses indicated a reduction in the likelihood of total (OR = 0.58; 95% CI, 0.37-0.92), major (OR = 0.36; 95% CI, 0.18-0.75), and orbital complications (OR = 0.38; 95% CI, 0.17-0.83). There was no demonstrated benefit of SAL at reducing revision surgery (OR = 0.64; 95% CI, 0.38-1.08), major hemorrhage (OR = 0.77; 95% CI, 0.29-2.06), or minor complications (OR = 0.85; 95% CI, 0.48-1.50). Due to the rare outcomes under investigation, the included primary studies largely lacked the power to identify a statistically meaningful effect of SAL in ESS. However, meta-analyses of primary studies demonstrated a decreased likelihood of total, major, and orbital complications in complex ESS with the use of SAL.

Evaluation of setup uncertainties for single-fraction SRS by comparing two different mask-creation methods

The purpose of this study was to evaluate the setup uncertainties for single-fraction stereotactic radiosurgery (SF-SRS) based on clinical data with two different mask-creation methods using pretreatment con-beam computed tomography imaging guidance. Dedicated frameless fixation Brain- LAB masks for 23 patients were created as a routine mask (R-mask) making method, as explained in the BrainLAB’s user manual. Alternative masks (A-masks), which were created by modifying the cover range of the R-masks for the patient’s head, were used for 23 patients. The systematic errors including these for each mask and stereotactic target localizer were analyzed, and the errors were calculated as the means ± standard deviations (SD) from the left-right (LR), superior-inferior (SI), anterior-posterior (AP), and yaw setup corrections. In addition, the frequencies of the threedimensional (3D) vector length were analyzed. The values of the mean setup corrections for the R-mask in all directions were < 0.7 mm and < 0.1°, whereas the magnitudes of the SDs were relatively large compared to the mean values. In contrast, the means and SDs of the A-mask were smaller than those for the R-mask with the exception of the SD in the AP direction. The means and SDs in the yaw rotational direction for the R-mask and the A-mask system were comparable. 3D vector shifts of larger magnitude occurred more frequently for the R-mask than the A-mask. The setup uncertainties for each mask with the stereotactic localizing system had an asymmetric offset towards the positive AP direction. The A-mask-creation method, which is capable of covering the top of the patient’s head, is superior to that for the R-mask, so the use of the A-mask is encouraged for SF-SRS to reduce the setup uncertainties. Moreover, careful mask-making is required to prevent possible setup uncertainties.

The PLORAS Database: A data repository for Predicting Language Outcome and Recovery After Stroke

The PLORAS Database is a relational repository of anatomical and functional imaging data that has primarily been acquired from stroke survivors, along with standardized scores on a wide range of sensory, motor and cognitive abilities, demographic details and medical history. As of January 2015, we have data from 750 patients with an expected accrual rate of 200 patients per year. Expansion will accelerate as we extend our collaborations. The main aim of the database is to Predict Language Outcome and Recovery After Stroke (PLORAS) on the basis of a single structural (anatomical) brain scan that indexes the stereotactic location and extent of brain damage. Predictions are made for individual patients by indicating how other patients with the most similar brain damage, cognitive abilities and demographic details recovered their language skills over time. Predictions are validated by longitudinal follow-ups of patients who initially presented with speech and language difficulties. The PLORAS Database can also be used to predict recovery of other cognitive abilities on the basis of anatomical brain scans. The functional imaging data can be used to understand the neural mechanisms that support recovery from brain damage; and all the data can be used to understand the main sources of inter-subject variability in structure–function mappings in the human brain. Data will be made available for sharing, subject to: funding, ethical approval and patient consent.

A three-dimensional digital atlas of the starling brain.

Because of their sophisticated vocal behaviour, their social nature, their high plasticity and their robustness, starlings have become an important model species that is widely used in studies of neuroethology of song production and perception. Since magnetic resonance imaging (MRI) represents an increasingly relevant tool for comparative neuroscience, a 3D MRI-based atlas of the starling brain becomes essential. Using multiple imaging protocols we delineated several sensory systems as well as the song control system. This starling brain atlas can easily be used to determine the stereotactic location of identified neural structures at any angle of the head. Additionally, the atlas is useful to find the optimal angle of sectioning for slice experiments, stereotactic injections and electrophysiological recordings. The starling brain atlas is freely available for the scientific community.

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.

Abstract

Rapid developments in imaging and radiation-delivery technology have fueled the application of small photon beams in stereotactic radiation therapy (SRT). Historically, stereotaxy referred to the use of a three-dimensional coordinate system to localize intracranial targets and has been more recently extensively developed in extracranial clinical situations. SRT involves stereotactic localization techniques combined with the delivery of multiple small photon fields in a few high-dose fractions. In SRT, the therapeutic ratio is optimized through delivery of highly conformal absorbed dose distributions with steep dose fall-off ensuring optimal absorbed dose in the target volume combined with minimal normal-tissue irradiation. Consistent with previous ICRU Reports 50 (ICRU, 1993), 62, (ICRU, 1999), and 83, (ICRU, 2010), this Report recommends a strict definition of target volumes (GTV, CTV) by reviewing imaging modalities used in clinical practice. This Report covers fundamentals of small-field dosimetry, treatment-planning algorithms, commissioning, and quality assurance for the existing delivery systems, as well as the role of image guidance during delivery. Finally, it recommends a framework for prescribing, recording, and reporting stereotactic radiotherapy, and covers most of the pathologies eligible for stereotactic delivery (malignant and non-malignant).

Accuracy of 3D fluoroscopy in cranial stereotactic surgery: A comparative study in phantoms and patients

To assess the precision and accuracy of 3D fluoroscopy (XT) in phantoms and patients compared to computed tomography (CT) in localizing stereotactic probes. Approval was obtained from the institutional research ethics board. The prospective phantom study was compared to a retrospective patient cohort. Accuracy was assessed by the mean error and precision by the mean dispersion between XT and CT with a cubic or a skull phantom containing metallic spheres installed on plates or along trajectories. Significance was assessed by Friedman's and Levene's test. Secondary endpoints were Euclidean error, other influences e.g. installed frame and radiation exposure. A total of 3,342 distances were assessed in 17 XT and 13 CT phantom scans. The cubic phantom showed mean distance errors of 0.33 mm (SD + -0.46 mm) for XT compared to 0.19 mm (SD + -0.83 mm) for CT scans (p = 0.0004) and a dispersion of 0.22 mm (XT) and 0.70 mm (CT). The dispersion was 0.36 mm with and 0.63 mm without a stereotactic frame (p < 0.0001). The mean Euclidean error was 0.72 mm (SD + -0.59 mm) in the skull phantom and 1.34 mm (SD + -0.82 mm) in the patient cohort. The effective dose was 0.65 mSv for the XT and 1.12 mSv for the CT. The accuracy of XT imaging in phantoms revealed a slightly lower accuracy but higher precision than the CT. The overall accuracy of XT was higher than that of the stereotactic frame allowing stereotactic localization with about half of the effective dose of a CT-scan.

Adaptive Treatment Planning and Online Setup Measurements to Guide Decision of Margin Size for Hypofractionated Intracranial Radiosurgery

Adaptive Treatment Planning and Online Setup Measurements to Guide Decision of Margin Size for Hypofractionated Intracranial Radiosurgery

SU‐E‐J‐89: GammaPlan MR to CT Image Registration Errors: Implications for Extend and Preplanned Treatments

Purpose: To compare the spatial errors in coordinate localization created by MR‐based stereotaxia in GammaPlan for two different Methods: direct stereotactic MR localization and MR co‐registration with a stereotactic CT. Methods: Seven patients underwent Gamma Knife SRS and were scanned with our clinical stereotactic MR and stereotactic CT protocols. In GammaPlan, the stereotactic coordinate system for each MR and CT was defined using the fiducials of the localizer. Separately, each MR was co‐registered (by the patient's anatomy) to the stereotactic CT using GammaPlan's automated co‐registration algorithm. A rigid transformation relationship was determined between the direct stereotactic MR (stereoMR) and the MR co‐registered to the stereotactic CT (coregMR). Spatial errors in coordinate definition between these two methods were calculated at the center of stereotactic space and at the centroid of the target. A total of seventeen MR scans were analyzed by this method including both axial and coronal acquisitions. Results: Mean errors in fiducial definition were found to be 0.6±0.3mm and 0.7±0.3mm for CT and MR, respectively. At the center of stereotactic space, the mean magnitude error in coordinate localization between stereoMR and coregMR was found to be 1.6±0.6mm. At the centroid of the target, the mean magnitude error was found to be 1.5±0.7mm. These results were statistically significant compared to the errors in fiducial definition (p&lt;0.002 for both). No statistically significant systematic errors along any axes were found in comparing stereoMR and coregMR coordinate localizations. Conclusion: Statistically significant differences were found in coordinate localizations between the two methods. These errors may primarily be due to sub‐optimal co‐registrations when using GammaPlan's automated registration algorithm. The magnitude of these errors may be clinically significant as they are on average greater than 1.5mm. Errors in co‐registration are important for preplanned SRS and Extend SRT treatments where direct stereotactic MR localization is not utilized.

SU‐C‐103‐02: Localization Accuracy of a Novel Prone Breast Stereotactic Immobilization and Localization System

Purpose: The GammaPodTM stereotactic radiotherapy device incorporates a novel stereotactic immobilization system and a fiducial based localization frame for the breast. We present the localization accuracy achieved with this stereotactic system through an IRB approved prospective protocol. Methods: GammaPodTM target localization is achieved using a dual layered immobilization breast cup under a negative pressure which has a built‐in stereotactic frame. Patient CT scans were attained using a pivoted patient loader which automatically lowers the patient from a vertical position to a horizontal prone‐lying position. We then performed two CT scans 30 minutes apart, simulating the pre‐treatment imaging and treatment sessions. The patient is disconnected from the patient loader after the first scan, but the immobilization cup remains on the breast under 150 mmHg of negative pressure until the end of the second scan. Evaluation of target localization was carried out via previously implanted surgical clips (two to five) and superficially positioned markers (three to seven). Scans were performed with 1 mm CT slice thickness. Results: The first 9 patients' results are presented with a total of 25 patients expected. Two patients were excluded due to improper fitting of the breast cup and patient comfort; one patient was excluded due to loss of breast cup pressure between the two scans. In the remaining six patients, the spatial reproducibility of internal markers was found to be 1.2 ± 1.0 mm (range 0.3−3.7) in between the two scans while the external marker positions differed by 0.9 ± 0.9 mm (range 0.1−3.9). The intrinsic accuracy of the stereotactic localization system found to be 0.1 ± 0.1 mm. Conclusion: The GammaPodTM target localization system is a unique approach to breast immobilization employing stereotactic principles. Preliminary results of this study suggest that the overall localization uncertainty of this system is 2.8 mm (95% CL).C. Yu and W. Regine have financial interests in Xcision Medical Systems.

GammaPod—A new device dedicated for stereotactic radiotherapy of breast cancer

This paper introduces a new external beam radiotherapy device named GammaPod that is dedicated for stereotactic radiotherapy of breast cancer. The design goal of the GammaPod as a dedicated system for treating breast cancer is the ability to deliver ablative doses with sharp gradients under stereotactic image guidance. Stereotactic localization of the breast is achieved by a vacuum-assisted breast immobilization cup with built-in stereotactic frame. Highly focused radiation is achieved at the isocenter due to the cross-firing from 36 radiation arcs generated by rotating 36 individual Cobalt-60 beams. The dedicated treatment planning system optimizes an optimal path of the focal spot using an optimization algorithm borrowed from computational geometry such that the target can be covered by 90%-95% of the prescription dose and the doses to surrounding tissues are minimized. The treatment plan is intended to be delivered with continuous motion of the treatment couch. In this paper the authors described in detail the gamma radiation unit, stereotactic localization of the breast, and the treatment planning system of the GammaPod system. A prototype GammaPod system was installed at University of Maryland Medical Center and has gone through a thorough functional, geometric, and dosimetric testing. The mechanical and functional performances of the system all meet the functional specifications. An image-guided breast stereotactic radiotherapy device, named GammaPod, has been developed to deliver highly focused and localized doses to a target in the breast under stereotactic image guidance. It is envisioned that the GammaPod technology has the potential to significantly shorten radiation treatments and even eliminate surgery by ablating the tumor and sterilizing the tumor bed simultaneously.

Nucleus accumbens stereotactic surgery: Achieving accuracy through area M

The nucleus accumbens(NA), a major pleasure center of the human brain, is a limbic-motor interface involved in several neurological and psychiatric disorders. During the last decade, this nucleus is also a deep brain stimulation target for selected patients. Purpose of this paper is to comment on the article entitled Stereotactic anatomy of the human nucleus accumbens: from applied mathematics to microsurgical accuracy which was recently published in Surgical and Radiologic Anatomy and is one of the latest articles on NA anatomy and surgery. The described results included a probabilitybased guide for in vivo(side-depended) stereotactic localization of the human NA and a standard for the NA, specific stereotactic zone of the human brain(which can be used in combination for an accurate stereotactic NA targeting). Furthermore, two specific stereotactically standard NA areas were found which could be used as abundant stereotactic guides for targeting of the anterior limb of the internal capsule, with electrode's contact 0(lowest) placed in the vicinity of the NA. However, the most important finding of this paper was standard area M(Mavridis' area), which is the most reliable stereotactically standard area of the human NA, regardless of side or gender, useful for highly accurate stereotacticNA targeting.

Quantitative verification of the keyhole concept: a comparison of area of exposure in the parasellar region via supraorbital keyhole, frontotemporal pterional, and supraorbital approaches

This study was designed to determine if the "keyhole concept," proposed by Perneczky's group, can be verified quantitatively. Fourteen (3 bilateral and 8 unilateral) sides of embalmed latex-injected cadaveric heads were dissected via 3 sequential craniotomy approaches: supraorbital keyhole, frontotemporal pterional, and supraorbital. Three-dimensional cartesian coordinates were recorded using a stereotactic localizer. The orthocenter of the ipsilateral anterior clinoid process, the posterior clinoid process, and the contralateral anterior clinoid process are expressed as a center point (the apex). Seven vectors project from the apex to their corresponding target points in a radiating manner on the parasellar skull base. Each 2 neighboring vectors border what could be considered a triangle, and the total area of the 7 triangles sharing the same apex was geometrically expressed as the area of exposure in the parasellar region. Values are expressed as the mean ± SD (mm(2)). The total area of exposure was as follows: supraorbital keyhole 1733.1 ± 336.0, pterional 1699.3 ± 361.9, and supraorbital 1691.4 ± 342.4. The area of exposure on the contralateral side was as follows: supraorbital keyhole 602.2 ± 194.7, pterional 595.2 ± 228.0, and supraorbital 553.3 ± 227.2. The supraorbital keyhole skull flap was 2.0 cm(2), and the skull flap size ratio was 1:5:6.5 (supraorbital keyhole/pterional/supraorbital). The area of exposure of the parasellar region through the smaller supraorbital keyhole approach is as adequate as the larger pterional and supraorbital approaches. The keyhole concept can be verified quantitatively as follows: 1) a wide area of exposure on the skull base can be obtained through a small keyhole skull opening, and 2) the side opposite the opening can also be visualized.