Considering inhomogeneities in Gamma Knife treatment planning: Factors affecting the loss of prescription dose coverage†.

OBJECT: To compare the consistency of the agreement between the Convolution and TMR10 algorithms using a homogeneous phantom and to identify target characteristics that lead to large changes in target isodose coverage when the Convolution algorithm is used in GammaPlan as opposed to the TMR10 algorithm. METHODS: The IROC phantom end-to-end test was performed and RTDose for both the TMR10 and Convolution algorithm were submitted for comparison to the measurement. Treatment plans for 16 patients and 26 different targets were retrospectively re-calculated with the Convolution algorithm when originally planned with the TMR10 algorithm. Multivariate regression was used to find statistically significant predictors of loss in target prescription isodose coverage. RESULTS: Both algorithms agreed well with the IROC TLD measurement (within 1 %) and slightly better agreement was seen in the film analysis for the Convolution algorithm. After multivariate regression, small target volumes, < 1cm from air cavity, and minimum dose to target were potential predictors of large percentage loss of prescription isodose coverage (p = 0.049, 0.026, and 0.002, respectively). CONCLUSION: Convolution and TMR10 appear to be equivalent in homogeneous situations. Some target characteristics have been identified that might be indications for use of the Convolution algorithm in clinical practice.

Evaluating the accuracy of geometrical distortion correction of magnetic resonance images for use in intracranial brain tumor radiotherapy.

AIM: Determine the 1) effectiveness of correction for gradient-non-linearity and susceptibility effects on both QUASAR GRID3D and CIRS phantoms; and 2) the magnitude and location of regions of residual distortion before and after correction. BACKGROUND: Using magnetic resonance imaging (MRI) as a primary dataset for radiotherapy planning requires correction for geometrical distortion and non-uniform intensity. MATERIALS AND METHODS: Phantom Study: MRI, computed tomography (CT) and cone beam CT images of QUASAR GRID3D and CIRS head phantoms were acquired. Patient Study: Ten patients were MRI-scanned for stereotactic radiosurgery treatment. Correction algorithm: Two magnitude and one phase difference image were acquired to create a field map. A MATLAB program was used to calculate geometrical distortion in the frequency encoding direction, and 3D interpolation was applied to resize it to match 3D T1-weighted magnetization-prepared rapid gradient-echo (MPRAGE) images. MPRAGE images were warped according to the interpolated field map in the frequency encoding direction. The corrected and uncorrected MRI images were fused, deformable registered, and a difference distortion map generated. RESULTS: Maximum deviation improvements: GRID3D , 0.27 mm y-direction, 0.07 mm z-direction, 0.23 mm x-direction. CIRS, 0.34 mm, 0.1 mm and 0.09 mm at 20-, 40- and 60-mm diameters from the isocenter. Patient data show corrections from 0.2 to 1.2 mm, based on location. The most-distorted areas are around air cavities, e.g. sinuses. CONCLUSIONS: The phantom data show the validity of our fast distortion correction algorithm. Patient-specific data are acquired in <2 min and analyzed and available for planning in less than a minute.

Gamma Knife® icon CBCT offers improved localization workflow for frame-based treatment.

OBJECT: The purpose of this study was to compare two methods of stereotactic localization in Gamma Knife treatment planning: cone beam computed tomography (CBCT) or fiducial. While the fiducial method is the traditional method of localization, CBCT is now available for use with the Gamma Knife Icon. This study seeks to determine whether a difference exists between the two methods and then whether one is better than the other regarding accuracy and workflow optimization. METHODS: Cone beam computed tomography was used to define stereotactic space around the Elekta Film Pinprick phantom and then treated with film in place. The same phantom was offset known amounts from center and then imaged with CBCT and registered with the reference CBCT image to determine if measured offsets matched those known. Ten frameless and 10 frame-based magnetic resonance imaging (MRI) to CBCT patient fusions were retrospectively evaluated using the TG-132 TRE method. The stereotactic coordinates defined by CBCT and traditional fiducials were compared on the Elekta 8 cm Ball phantom, an anthropomorphic phantom, and actual patient data. Offsets were introduced to the anthropomorphic phantom in the stereotactic frame and CBCT's ability to detect those offsets was determined. RESULTS: Cone beam computed tomography defines stereotactic space well within the established limits of the mechanical alignment system. The CBCT to CBCT registration can detect offsets accurately to within 0.1 mm and 0.5°. In all cases, some disagreement existed between fiducial localization and that of CBCT which in some cases was small, but also was as high as 0.43 mm in the phantom domain and as much as 1.54 mm in actual patients. CONCLUSION: Cone beam computed tomography demonstrates consistent accuracy in defining stereotactic space. Since both localization methods do not agree with each other consistently, the more reliable method must be identified. Cone beam computed tomography can accurately determine offsets occurring within stereotactic space that would be nondiscernible utilizing the fiducial method and seems to be more reliable. Using CBCT localization offers the opportunity to streamline workflow both from a patient and clinic perspective and also shows patient position immediately prior to treatment.

Optimizing MRI sequences and images for MRI-based stereotactic radiosurgery treatment planning.

AIM: Development of MRI sequences and processing methods for the production of images appropriate for direct use in stereotactic radiosurgery (SRS) treatment planning. BACKGROUND: MRI is useful in SRS treatment planning, especially for patients with brain lesions or anatomical targets that are poorly distinguished by CT, but its use requires further refinement. This methodology seeks to optimize MRI sequences to generate distortion-free and clinically relevant MR images for MRI-only SRS treatment planning. MATERIALS AND METHODS: We used commercially available SRS MRI-guided radiotherapy phantoms and eight patients to optimize sequences for patient imaging. Workflow involved the choice of correct MRI sequence(s), optimization of the sequence parameters, evaluation of image quality (artifact free and clinically relevant), measurement of geometrical distortion, and evaluation of the accuracy of our offline correction algorithm. RESULTS: CT images showed a maximum deviation of 1.3 mm and minimum deviation of 0.4 mm from true fiducial position for SRS coordinate definition. Interestingly, uncorrected MR images showed maximum deviation of 1.2 mm and minimum of 0.4 mm, comparable to CT images used for SRS coordinate definition. After geometrical correction, we observed a maximum deviation of 1.1 mm and minimum deviation of only 0.3 mm. CONCLUSION: Our optimized MRI pulse sequences and image correction technique show promising results; MR images produced under these conditions are appropriate for direct use in SRS treatment planning.

Use of intraoperative fluorescein sodium fluorescence to improve the accuracy of tissue diagnosis during stereotactic needle biopsy of high-grade gliomas.

BACKGROUND: Stereotactic needle biopsy is valuable for tissue diagnosis of suspected high-grade gliomas, but limited by a sampling error that can lead to inappropriate grading of the tumor or failure to provide diagnosis. Increasing the number of biopsy attempts can increase morbidity. The authors designed a protocol to increase safety and efficiency of the procedure. METHODS: Six consecutive patients with suspected high-grade gliomas who were not candidates for cytoreductive surgery underwent fluorescein-guided stereotactic needle biopsy. All received an injection of 3 mg/kg fluorescein sodium during anesthesia induction. Samples were obtained and observed under a microscope-integrated fluorescent module. If the initial specimens were fluorescent, the procedure was complete if the pathologist confirmed diagnostic tissue. Additional specimens were obtained only at the pathologist's request. An independent neuropathologist later analyzed and graded samples for diagnostic value, tumor, and necrosis. This information was correlated to the degree of intraoperative fluorescent signal in biopsy samples. RESULTS: During six biopsy procedures, 26 specimens were obtained: 15 (58 %) fluorescent and 11 (42 %) nonfluorescent. All fluorescent specimens contained diagnostic tissue appropriate for tumor grading. Of 11 nonfluorescent specimens, four (36 %) did not contain tumor, three (27 %) contained minor hypercellularity or gliosis, and four (36 %) contained tumor with a high proportion of necrosis. All six tumors were diagnosed as glioblastoma multiforme. The sensitivity and specificity for fluorescein fluorescence was 79 % and 100 %, respectively. CONCLUSIONS: Fluorescein fluorescence may improve diagnostic accuracy and expedite stereotactic biopsy procedures.

Modified periinsular hemispherotomy: operative anatomy and technical nuances.

Surgical options for pediatric patients with marked dysfunction of a single epileptogenic hemisphere have evolved over time. Complications resulting from highly resective operations such as anatomical hemispherectomy, including superficial siderosis and secondary hydrocephalus, have led to the development of less resective and more disconnective functional hemispherectomy. Functional hemispherectomy has recently given rise to hemispherotomy, the least resective operation primarily aimed at disconnecting the abnormal hemisphere. Hemispherotomy is effective in decreasing seizure frequency and most likely decreases the risk of postoperative complications when compared with its predecessors. Hemispherotomy is a technically challenging operation that requires a thorough understanding of 3D cerebral anatomy to ensure adequate hemispheric disconnection without placing important structures at risk. The details of germane operative anatomy are not currently available because of the difficulty in exposing this operative anatomy adequately in cadavers to prepare detailed instructive illustrations. Using 3D graphic models, the authors have prepared 2D overlay illustrations to discuss the relevant operative nuances for a modified form of this procedure. Through hemispherotomy, experienced surgeons can effectively treat patients with unilateral epileptogenic hemisphere dysfunction while limiting potential complications.

Pituitary macroadenoma causing symptomatic internal carotid artery compression: surgical treatment through transsphenoidal tumor resection.

Pituitary macroadenomas can invade the cavernous sinus and rarely cause occlusion of the internal carotid artery (ICA). Most patients with symptomatic obstruction of the ICA by a pituitary tumor have been reported as a result of apoplexy. The authors review the literature about this condition and report a 48-year-old man who presented with transient ischemic attacks leading to a stroke. Imaging studies demonstrated complete occlusion of the left ICA and critical narrowing of the right ICA at the level of the clinoid processes, most likely due to macroadenoma mass effect. There was no radiologic evidence of apoplexy. Surgical resection of the tumor and ICA decompression via the transsphenoidal route resulted in prevention of further symptoms. Histopathologic analysis confirmed a nonfunctioning pituitary adenoma without evidence of hemorrhage or intratumoral infarction. This patient, to the authors' knowledge, is the first documented patient with symptomatic carotid compression by a pituitary adenoma without evidence of apoplexy.

Intraoperative fluorescence-guided resection of high-grade gliomas: a comparison of the present techniques and evolution of future strategies.

OBJECTIVE: Fluorescence guidance has a demonstrated potential in maximizing the extent of high-grade glioma resection. Different fluorophores (fluorescent biomarkers), including 5-aminolevulinic acid (5-ALA) and fluorescein, have been examined with the use of several imaging techniques. Our goal was to review the state of this technology and discuss strategies for more widespread adoption. METHODS: We performed a Medline search using the key words "fluorescence," "intraoperative fluorescence-guided resection," "intraoperative image-guided resection," and "brain glioma" for articles from 1960 until the present. This initial search revealed 267 articles. Each abstract and article was reviewed and the reference lists from select articles were further evaluated for relevance. A total of 64 articles included information about the role of fluorescence in resection of high-grade gliomas and therefore were selectively included for our analysis. RESULTS: 5-ALA and fluorescein sodium have shown promise as fluorescent markers in detecting residual tumor intraoperatively. These techniques have demonstrated a significant increase in the extent of tumor resection. Regulatory barriers have limited the use of 5-ALA and technological challenges have restricted the use of fluorescein and its derivatives in the United States. Limitations to this technology currently exist, such as the fact that fluorescence at tumor margins is not always reliable for identification of tumor-brain interface. CONCLUSIONS: These techniques are safe and effective for increasing gross total resection. The development of more tumor-specific fluorophores is needed to resolve problems with subjective interpretation of fluorescent signal at tumor margins. Techniques such as quantum dots and polymer or iron oxide-based nanoparticles have shown promise as potential future tools.

A surgical technique to expand the operative corridor for supracerebellar infratentorial approaches: technical note.

BACKGROUND: The supracerebellar infratentorial approach is a commonly used route in neurosurgery. It provides a narrow and deep corridor to the dorsal midbrain and pineal region. The authors describe a surgical technique to expand the operative corridor and the surgeon's working angles during this approach. METHODS: Thirteen cases of patients who underwent resection of their lesions using this extended approach were reviewed. During their suboccipital craniotomy, additional bone over the transverse sinus (paramedian approach) and the confluence of the sinuses (midline approach) were removed. Two sutures (tentorial stay sutures) were anchored to the tentorium anterior to the transverse sinus and tension was applied. A video narrated by the senior author describes the details of technique. RESULTS: This additional bone removal and tentorial stay sutures led to gentle elevation of the tentorium and partial mobilization of the dural venous sinuses superiorly. This technique enhanced operative viewing through improved illumination and expanded working angles for microsurgical instruments while minimizing the need for fixed retractors and extensive cerebellar retraction. All patients underwent satisfactory removal of their lesions. No patient suffered from any related complication. CONCLUSION: The use of stay sutures anchored on the tentorium is a simple and effective technique that expands the surgical corridor during supracerebellar infratentorial approaches.

Intraoperative fluorescence for resection of hemangioblastomas.

BACKGROUND: Resection of hemangioblastomas can be challenging due to their high vascularity and intimate association with neighboring cerebrovascular structures. The authors present their intraoperative findings using fluorescein angiography and fluorescence for removal of hemangioblastomas in an attempt to improve the safety and extent of resection. METHODS: From April through August 2012, four patients were diagnosed with hemangioblastomas, 3 in the cerebellum and 1 in the medulla oblongata. Low-dose (4 mg/kg) sodium fluorescein was injected intravenously immediately before microdissection. The area of interest was inspected through a microscope-integrated fluorescent module. RESULTS: In three superficially located tumors, the vascular pattern of feeding and draining vessels could be easily identified with fluorescein angiography. The resection of the tumors was guided using real-time fluorescence mode. For each patient, histopathologic examination of the lesion confirmed the diagnosis of hemangioblastoma. All samples of fluorescent tissue resected were confirmed to contain tumor. No patient experienced any complication. CONCLUSION: Low-dose sodium fluorescein used in conjunction with a microscope-integrated fluorescence module is a potentially useful tool for localization, vascular characterization, and resection of hemangioblastomas.

Current neurosurgical management of glossopharyngeal neuralgia and technical nuances for microvascular decompression surgery.

Glossopharyngeal neuralgia (GPN) is an uncommon facial pain syndrome often misdiagnosed as trigeminal neuralgia. The rarity of this condition and its overlap with other cranial nerve hyperactivity syndromes often leads to a significant delay in diagnosis. The surgical procedures with the highest rates of pain relief for GPN are rhizotomy and microvascular decompression (MVD) of cranial nerves IX and X. Neurovascular conflict at the level of the root exit zone of these cranial nerves is believed to be the cause of this pain syndrome in most cases. Vagus nerve rhizotomy is usually reserved for cases in which vascular conflict is not evident. A review of the literature reveals that although the addition of cranial nerve X rhizotomy may improve the chances of long-term pain control, this maneuver also increases the risk of permanent dysphagia and vocal cord paralysis. The risks of this procedure have to be carefully weighed against its benefits. Based on the authors' experience, careful patient selection with a thorough exploratory operation most often leads to identification of the site of vascular conflict, obviating the need for cranial nerve X rhizotomy.

Technical principles and neurosurgical applications of fluorescein fluorescence using a microscope-integrated fluorescence module.

BACKGROUND: Fluorescent technology has recently become a valuable tool in the surgical management of neoplastic and vascular lesions. The availability of microscope-integrated fluorescent modules has facilitated incorporation of this technology within the microsurgical workflow. The currently available microscope integrated modules use 5-aminolevulinic acid (5-ALA) and indocyanine green (ICG) as fluorophores. METHODS: Fluorescein sodium is a fluorescent molecule that has been used specifically in ophthalmology for the treatment of retinal angiography. A new microscope-integrated fluorescent module has been recently developed for fluorescein. We employed this technology to maximize resection of tumors and perform intraoperative angiography to guide microsurgical management of aneurysms and arteriovenous malformations. RESULTS: Fluorescein fluorescence allows the surgeon to appreciate fluorescent structures through the oculars while visualizing non-fluorescent tissues in near natural colors. Therefore, the operator can proceed with microsurgery under the fluorescent mode. We present three representative cases in which the use of fluorescein fluorescence was found useful in the surgeon's decision making during surgery. CONCLUSIONS: The applications of this new microscope-integrated fluorescent module are multiple, and include vascular and oncologic neurosurgery. Further clinical investigations with large patient cohorts are needed to fully establish the role of this new technology.

Technical nuances for surgery of insular gliomas: lessons learned.

Insular gliomas were traditionally considered a nonsurgical entity due to the high morbidity associated with resection. For the past 20 years, advances in microsurgical and brain mapping techniques have allowed neurosurgeons to resect insular gliomas with acceptable morbidity rates. Maximizing the extent of resection is nowadays the goal of surgery since this has proven to be an independent factor contributing to longer survival. Despite much progress, insular tumors remain a challenge for the neurosurgeon due to the complex anatomy of the region and technical expertise required to minimize morbidity during surgery. Herein, the authors describe the current surgical nuances, based on their experience and a literature review, that will allow the surgeon to achieve a thorough resection while ensuring patient safety. The key factors for successful surgery in the insular region include detailed knowledge of the surgical anatomy, mastery of the nuances of cortical and subcortical mapping methods, and meticulous microsurgical technique.