Gamma knife radiosurgery as a lesioning technique in movement disorder surgery

Stereotatic radiosurgery for the treatment of motor symptoms in Parkinson's disease: A systematic review

BACKGROUND

Stereotaxic Radiosurgery (SRS) is a non-invasive lesioning technique for movement disorders when patients cannot undergo DBS due to medical comorbidities.

OBJECTIVE

To describe and summarize the literature on SRS's application and physical parameters for Parkinson's disease (PD) motor symptoms.

METHODS

The MEDLINE/PUBMED and EMBASE databases were searched in July 2022 following the PRISMA guideline. Two independent reviewers screened data from 425 articles. The level of evidence followed the Oxford Centre for Evidence-Based Medicine. Pertinent details for each study regarding participants, physical parameters, and results were extracted.

RESULTS

Twelve studies reported that 454 PD patients underwent Gamma KnifeⓇ (GK). The mean improvement time of the treated symptoms was three months after GK. Tremor is the most common symptom investigated, with success rates ranging from 47.5% to 93.9%. Few studies were conducted for caudatotomy (GKC) and pallidotomy (GKP), which presented an improvement for dyskinesia and bradykinesia. Physical parameters were similar with doses ranging from 110 to 200 Gy, use of a 4-mm collimator with an advanced imaging locator system, and coordinates were obtained from available stereotactic atlases.

CONCLUSIONS

GK thalamotomy is a good alternative for treating tremor; however, its effects are delayed, and there are cases in which it can regress after years. The outcomes of GKC and GKP seem to be promising. The existing studies are more limited, and effects need to be better investigated.

A Systematic Review Comparing Focused Ultrasound Surgery With Radiosurgery for Essential Tremor

BACKGROUND

Focused ultrasound (FUS-T) and stereotactic radiosurgery thalamotomy (SRS-T) targeting the ventral intermediate nucleus are effective incisionless surgeries for essential tremor (ET). However, their efficacy for tremor reduction and, importantly, adverse event incidence have not been directly compared.

OBJECTIVE

To present a comprehensive systematic review with network meta-analysis examining both efficacy and adverse events (AEs) of FUS-T vs SRS-T for treating medically refractory ET.

METHODS

We conducted a systematic review and network meta-analysis according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, using the PubMed and Embase databases. We included all primary FUS-T/SRS-T studies with approximately 1-year follow-up, with unilateral Fahn-Tolosa-Marin Tremor Rating Scale or Clinical Rating Scale for Tremor scores prethalamotomy/post-thalamotomy and/or AEs. The primary efficacy outcome was Fahn-Tolosa-Marin Tremor Rating Scale A+B score reduction. AEs were reported as an estimated incidence.

RESULTS

Fifteen studies of 464 patients and 3 studies of 62 patients met inclusion criteria for FUS-T/SRS-T efficacy comparison, respectively. Network meta-analysis demonstrated similar tremor reduction between modalities (absolute tremor reduction: FUS-T: -11.6 (95% CI: -13.3, -9.9); SRS-T: -10.3 (95% CI: -14.2, -6.0). FUS-T had a greater 1-year adverse event rate, particularly imbalance and gait disturbances (10.5%) and sensory disturbances (8.3%). Contralateral hemiparesis (2.7%) often accompanied by speech impairment (2.4%) were most common after SRS-T. There was no correlation between efficacy and lesion volume.

CONCLUSION

Our systematic review found similar efficacy between FUS-T and SRS-T for ET, with trend toward higher efficacy yet greater adverse event incidence with FUS-T. Smaller lesion volumes could mitigate FUS-T off-target effects for greater safety.

Ablative brain surgery: an overview

Background: Ablative therapies have been used for the treatment of neurological disorders for many years. They have been used both for creating therapeutic lesions within dysfunctional brain circuits and to destroy intracranial tumors and space-occupying masses. Despite the introduction of new effective drugs and neuromodulative techniques, which became more popular and subsequently caused brain ablation techniques to fall out favor, recent technological advances have led to the resurgence of lesioning with an improved safety profile. Currently, the four main ablative techniques that are used for ablative brain surgery are radiofrequency thermoablation, stereotactic radiosurgery, laser interstitial thermal therapy and magnetic resonance-guided focused ultrasound thermal ablation. Object: To review the physical principles underlying brain ablative therapies and to describe their use for neurological disorders. Methods: The literature regarding the neurosurgical applications of brain ablative therapies has been reviewed. Results: Ablative treatments have been used for several neurological disorders, including movement disorders, psychiatric disorders, chronic pain, drug-resistant epilepsy and brain tumors. Conclusions: There are several ongoing efforts to use novel ablative therapies directed towards the brain. The recent development of techniques that allow for precise targeting, accurate delivery of thermal doses and real-time visualization of induced tissue damage during the procedure have resulted in novel techniques for cerebral ablation such as magnetic resonance-guided focused ultrasound or laser interstitial thermal therapy. However, older techniques such as radiofrequency thermal ablation or stereotactic radiosurgery still have a pivotal role in the management of a variety of neurological disorders.

A meta-analysis of outcomes and complications of magnetic resonance-guided focused ultrasound in the treatment of essential tremor

OBJECTIVE Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel technique that uses high-intensity focused ultrasound to achieve target ablation. Like a lens focusing the sun's rays, the ultrasound waves are focused to generate heat. This therapy combines the noninvasiveness of Gamma Knife thalamotomy and the real-time ablation of deep brain stimulation with acceptable complication rates. The aim of this study was to analyze the overall outcomes and complications of MRgFUS in the treatment of essential tremor (ET). METHODS A meta-analysis in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was made by searching PubMed, Cochrane library database, Web of Science, and Cumulative Index to Nursing and Allied Health Literature (CINAHL). Patients with the diagnosis of ET who were treated with MRgFUS were included in the study. The change in the Clinical Rating Scale for Tremor (CRST) score after treatment was analyzed. The improvement in disability was assessed with the Quality of Life in Essential Tremor Questionnaire (QUEST) score. The pooled data were analyzed by the DerSimonian-Laird random-effects model. Tests for bias and heterogeneity were performed. RESULTS Nine studies with 160 patients who had ET were included in the meta-analysis. The ventral intermediate nucleus was the target in 8 of the studies. The cerebellothalamic tract was targeted in 1 study. There was 1 randomized controlled trial, 6 studies were retrospective, and 2 were prospective. The mean number of sonications given in various studies ranged from 11 ± 3.2 to 22.5 ± 7.5 (mean ± SD). The maximum delivered energy ranged from 10,320 ± 4537 to 14,497 ± 6695 Joules. The mean of peak temperature reached ranged from 53°C ± 2.3°C to 62.0°C ± 2.5°C. On meta-analysis with the random-effects model, the pooled percentage improvements in the CRST Total, CRST Part A, CRST Part C, and QUEST scores were 62.2%, 62.4%, 69.1%, and 46.5%, respectively. Dizziness was the most common in-procedure complication, occurring in 45.5%, followed by nausea and vomiting in 26.85% (pooled percentage). At 3 months, ataxia was the most common complication, occurring in 32.8%, followed by paresthesias in 25.1% of the patients. At 12 months posttreatment, the ataxia had significantly recovered and paresthesias became the most common persisting complication, at 15.3%. CONCLUSIONS The MRgFUS therapy for ET significantly improves the CRST scores and improves the quality of life in patients with ET, with an acceptable complication rate. Therapy with MRgFUS is a promising frontier in functional neurosurgery.

Stereotactic radiosurgery for tremor: systematic review

OBJECTIVE

The aim of this systematic review is to offer an objective summary of the published literature relating to stereotactic radiosurgery (SRS) for tremor and consensus guideline recommendations.

METHODS

This systematic review was performed up to December 2016. Article selection was performed by searching the MEDLINE (PubMed) and EMBASE electronic bibliographic databases. The following key words were used: "radiosurgery" and "tremor" or "Parkinson's disease" or "multiple sclerosis" or "essential tremor" or "thalamotomy" or "pallidotomy." The search strategy was not limited by study design but only included key words in the English language, so at least the abstract had to be in English.

RESULTS

A total of 34 full-text articles were included in the analysis. Three studies were prospective studies, 1 was a retrospective comparative study, and the remaining 30 were retrospective studies. The one retrospective comparative study evaluating deep brain stimulation (DBS), radiofrequency thermocoagulation (RFT), and SRS reported similar tremor control rates, more permanent complications after DBS and RFT, more recurrence after RFT, and a longer latency period to clinical response with SRS. Similar tremor reduction rates in most of the reports were observed with SRS thalamotomy (mean 88%). Clinical complications were rare and usually not permanent (range 0%-100%, mean 17%, median 2%). Follow-up in general was too short to confirm long-term results.

CONCLUSIONS

SRS to the unilateral thalamic ventral intermediate nucleus, with a dose of 130-150 Gy, is a well-tolerated and effective treatment for reducing medically refractory tremor, and one that is recommended by the International Stereotactic Radiosurgery Society.

Tests of clustering thalamic nuclei based on various dMRI models in the squirrel monkey brain

Background

Clustering thalamic nuclei is important for both research and clinical purposes. For example, ventral intermediate nuclei in thalami serve as targets in both deep brain stimulation neurosurgery and radiosurgery for treating patients suffering from movement disorders (e.g., Parkinson's disease and essential tremor). Diffusion magnetic resonance imaging (dMRI) is able to reflect tissue microstructure in the central nervous system via fitting different models, such as, the diffusion tensor (DT), constrained spherical deconvolution (CSD), neurite orientation dispersion and density imaging (NODDI), diffusion kurtosis imaging (DKI) and the spherical mean technique (SMT).

Purpose

To test which of the above-mentioned dMRI models is better for thalamic parcellation, we proposed a framework of k-means clustering, implemented it on each model, and evaluated the agreement with histology.

Method

An ex vivo monkey brain was scanned in a 9.4T MRI scanner at 0.3mm resolution with b values of 3000, 6000, 9000 and 12000 s/mm². K-means clustering on each thalamus was implemented using maps of dMRI models fitted to the same data. Meanwhile, histological nuclei were identified by AChE and Nissl stains of the same brain. Overall agreement rate and agreement rate for each nucleus were calculated between clustering and histology. Sixteen thalamic nuclei on each hemisphere were included.

Results

Clustering with the DKI model has slightly higher overall agreement rate but clustering with other dMRI models result in higher agreement rate in some nuclei.

Conclusion

dMRl models should be carefully selected to better parcellate the thalamus, depending on the specific purpose of the parcellation.

Treatment of the ventral intermediate nucleus for medically refractory tremor: A cost-analysis of stereotactic radiosurgery versus deep brain stimulation

INTRODUCTION

Medically refractory tremor treatment has evolved over the past half-century from intraoperative thalamotomy to deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM). Within the past 15years, unilateral radiosurgical VIM thalamotomy has emerged as a comparably efficacious treatment modality.

METHODS

An extensive literature search of VIM DBS series was performed; the total cost of VIM DBS was calculated from hospitals geographically representative of the entire United States using current procedural terminology and work relative value unit (RVU) codes. The 2016 Medicare Ambulatory Payment Classification for stereotactic radiosurgery (SRS) was added to the work RVU to determine the total cost of VIM SRS for both Gamma Knife and linear accelerator SRS. Cost estimates assumed that VIM DBS was performed without intraoperative microelectrode recording.

RESULT

The mean unilateral VIM DBS cost was $17,932.41 per patient. For SRS VIM, the total costs for Gamma Knife ($10,811.77) and linear accelerator ($10,726.40) were 40% less expensive than for unilateral VIM DBS.

CONCLUSION

Radiosurgery of the VIM is 40% less expensive than unilateral VIM DBS in treatment of medically refractory tremor, regardless of radiosurgical modality. This finding argues for increased radiation oncology involvement in the management of medically refractory tremor patients.

Stereotactic radiosurgery for essential tremor: Retrospective analysis of a 19-year experience

BACKGROUND

Essential Tremor (ET) is a common movement disorder that can be disabling. Initial treatment is in the form of medical therapies. Patients with medically refractory ET seek surgical intervention which include radiofrequency thalamotomy, deep brain stimulation, and radiosurgical thalamotomy. Radiosurgical thalamotomy is a minimally invasive surgical option which is especially valuable for elderly and high surgical risk patients.

OBJECTIVE

The purpose of this study was to retrospectively analyze the outcomes of stereotactic radiosurgery for patients suffering from medically refractory essential tremor.

METHODS

During a 19-year period (1996-2015), 73 patients underwent gamma knife thalamotomy for intractable essential tremor. A median central dose of 140 Gy (range, 130-150) was delivered to the nucleus ventralis intermedius through a single 4-mm isocenter. We used the Fahn-Tolosa-Marin clinical tremor rating scale to score tremor, handwriting, drawing, and ability to drink fluids. The median time to last follow-up was 28 months (range, 6-152).

RESULTS

After gamma knife thalamotomy, 93.2% improved in tremor. Forty-four patients (60.3%) experienced tremor arrest or barely perceptible tremor. Eighteen patients (24.7%) noted tremor arrest and complete restoration of motor function. Tremor improvement was sustained at last follow-up in 96% of patients who experience tremor relief. Mean tremor score improved from 3.19 before to 1.27 after gamma knife thalamotomy (P < 0.0001). Mean handwriting score improved from 2.97 to 1.25 (P < 0.0001). Mean drawing score improved from 3.16 to 1.26 (P < 0.0001). Mean drinking score improved from 3.14 to 1.56 (P < 0.0001). Imaging follow-up showed three types of lesions: enhancing lesion, streaking along internal capsule on fluid-attenuated inversion recovery, and significant reactive changes. Three patients (4%) experienced temporary adverse radiation effects.

CONCLUSION

Radiosurgery is a safe and valuable treatment option for medically refractory essential tremor, especially for the elderly or those with high surgical risk for DBS or radiofrequency thalamotomy. © 2017 International Parkinson and Movement Disorder Society.

Gamma-knife subcaudate tractotomy for treatment-resistant depression and target characteristics: a case report and review

Stereotactic subcaudate tractotomy has previously been suggested to be an effective treatment for depression. This is the first study to report the use of gamma-knife subcaudate tractotomy for treatment-resistant depression. A 49-year-old woman with major depressive disorder had been treated for 30 years, with nine suicide attempts during that time. The right and left target maximum diameter was 11 mm within 50 % isodose lines. The target was located more posteriorly and inferiorly than the subgenual cingulate target typically used for deep-brain stimulation. The maximum radiation dose was 130 Gy. During the 4 months after surgery, the patient improved gradually from 23 to 4 according to the Hamilton Rating Scale for Depression and antidepressant medication was discontinued. Target-sized focal lesions were identified and no edema was seen postoperatively. No aggravation or neurologic deficit occurred during the 2.5 years of follow-up. Gamma-knife subcaudate tractotomy for depression is a minimally invasive technique. Investigations of the effectiveness and safety profile in a larger group are warranted.

The role of diffusion tensor imaging tractography for Gamma Knife thalamotomy planning

OBJECTIVE

The role of tractography in Gamma Knife thalamotomy (GK-T) planning is still unclear. Pyramidal tractography might reduce the risk of radiation injury to the pyramidal tract and reduce motor complications.

METHODS

In this study, the ventralis intermedius nucleus (VIM) targets of 20 patients were bilaterally defined using Iplannet Stereotaxy Software, according to the anterior commissure–posterior commissure (AC-PC) line and considering the localization of the pyramidal tract. The 40 targets and tractography were transferred as objects to the GammaPlan Treatment Planning System (GP-TPS). New targets were defined, according to the AC-PC line in the functional targets section of the GP-TPS. The target offsets required to maintain the internal capsule (IC) constraint of < 15 Gy were evaluated. In addition, the strategies available in GP-TPS to maintain the minimum conventional VIM target dose at > 100 Gy were determined.

RESULTS

A difference was observed between the positions of both targets and the doses to the IC. The lateral (x) and the vertical (z) coordinates were adjusted 1.9 mm medially and 1.3 mm cranially, respectively. The targets defined considering the position of the pyramidal tract were more medial and superior, based on the constraint of 15 Gy touching the object representing the IC in the GP-TPS. The best strategy to meet the set constraints was 90° Gamma angle (GA) with automatic shaping of dose distribution; this was followed by 110° GA. The worst GA was 70°. Treatment time was substantially increased by the shaping strategy, approximately doubling delivery time.

CONCLUSIONS

Routine use of DTI pyramidal tractography might be important to fine-tune GK-T planning. DTI tractography, as well as anisotropy showing the VIM, promises to improve Gamma Knife functional procedures. They allow for a more objective definition of dose constraints to the IC and targeting. DTI pyramidal tractography introduced into the treatment planning may reduce the incidence of motor complications and improve efficacy. This needs to be validated in a large clinical series.

Application of radiosurgical techniques to produce a primate model of brain lesions

Behavioral analysis of subjects with discrete brain lesions provides important information about the mechanisms of various brain functions. However, it is generally difficult to experimentally produce discrete lesions in deep brain structures. Here we show that a radiosurgical technique, which is used as an alternative treatment for brain tumors and vascular malformations, is applicable to create non-invasive lesions in experimental animals for the research in systems neuroscience. We delivered highly focused radiation (130-150 Gy at ISO center) to the frontal eye field (FEF) of macaque monkeys using a clinical linear accelerator (LINAC). The effects of irradiation were assessed by analyzing oculomotor performance along with magnetic resonance (MR) images before and up to 8 months following irradiation. In parallel with tissue edema indicated by MR images, deficits in saccadic and smooth pursuit eye movements were observed during several days following irradiation. Although initial signs of oculomotor deficits disappeared within a month, damage to the tissue and impaired eye movements gradually developed during the course of the subsequent 6 months. Postmortem histological examinations showed necrosis and hemorrhages within a large area of the white matter and, to a lesser extent, in the adjacent gray matter, which was centered at the irradiated target. These results indicated that the LINAC system was useful for making brain lesions in experimental animals, while the suitable radiation parameters to generate more focused lesions need to be further explored. We propose the use of a radiosurgical technique for establishing animal models of brain lesions, and discuss the possible uses of this technique for functional neurosurgical treatments in humans.

Gamma Knife thalamotomy for tremor in the magnetic resonance imaging era

Object

The surgical management of disabling tremor has gained renewed vigor with the availability of deep brain stimulation. However, in the face of an aging population of patients with increasing surgical comorbidities, noninvasive approaches for tremor management are needed. The authors' purpose was to study the technique and results of stereotactic radiosurgery performed in the era of MRI targeting.

Methods

The authors evaluated outcomes in 86 patients (mean age 71 years; number of procedures 88) who underwent a unilateral Gamma Knife thalamotomy (GKT) for tremor during a 15-year period that spanned the era of MRI-based target selection (1996–2011). Symptoms were related to essential tremor in 48 patients (19 age ≥ 80 years and 3 age ≥ 90 years), Parkinson disease in 27 patients (11 age ≥ 80 years [1 patient underwent bilateral procedures]), and multiple sclerosis in 11 patients (1 patient underwent bilateral procedures). A single 4-mm isocenter was used to deliver a maximum dose of 140 Gy to the posterior-inferior region of the nucleus ventralis intermedius. The Fahn-Tolosa-Marin clinical tremor rating scale was used to grade tremor, handwriting, and ability to drink. The median follow-up was 23 months.

Results

The mean tremor score was 3.28 ± 0.79 before and 1.81 ± 1.15 after (p < 0.0001) GKT; the mean handwriting score was 2.78 ± 0.82 and 1.62 ± 1.04, respectively (p < 0.0001); and the mean drinking score was 3.14 ± 0.78 and 1.80 ± 1.15, respectively (p < 0.0001). After GKT, 57 patients (66%) showed improvement in all 3 scores, 11 patients (13%) in 2 scores, and 2 patients (2%) in just 1 score. In 16 patients (19%) there was a failure to improve in any score. Two patients developed a temporary contralateral hemiparesis, 1 patient noted dysphagia, and 1 sustained facial sensory loss.

Conclusions

Gamma Knife thalamotomy in the MRI era was a safe and effective noninvasive surgical strategy for medically refractory tremor in the elderly or those with contraindications to deep brain stimulation or stereotactic radiofrequency (thermal) thalamotomy.

[Stereotactic radiosurgery for movement disorders]

Nowadays, functional neurosurgery is an established treatment for movement disorders such as Parkinson's disease, essential tremor, and dystonia. The effectiveness and safety of neuromodulation procedures (deep brain stimulation) replaced in the last years ablative irreversible stereotactic lesions for movement disorders. Stereotactic radiosurgery with gamma knife is a non-invasive form of treatment for movement disorders. The main limitation of stereotactic radiosurgery is the impossibility of electrophysiological confirmation of the target structure. Nevertheless, patients with advanced age and significant medical conditions that preclude classic open stereotactic procedures or patients who must receive anticoagulation therapy may gain great functional benefit using gamma knife stereotactic radiosurgery.

Stereotactic radiosurgery for movement disorders

Initially designed for the treatment of functional brain targets, stereotactic radiosurgery (SRS) has achieved an important role in the management of a wide range of neurosurgical pathologies. The interest in the application of the technique for the treatment of pain, and psychiatric and movement disorders has returned in the beginning of the 1990s, stimulated by the advances in neuroimaging, computerized dosimetry, treatment planning software systems, and the outstanding results of radiosurgery in other brain diseases. Since SRS is a neuroimaging-guided procedure, without the possibility of neurophysiological confirmation of the target, deep brain stimulation (DBS) and radiofrequency procedures are considered the best treatment options for movement-related disorders. Therefore, SRS is an option for patients who are not suitable for an open neurosurgical procedure. SRS thalamotomy provided results in tremor control, comparable to radiofrequency and DBS. The occurrence of unpredictable larger lesions than expected with permanent neurological deficits is a limitation of the procedure. Improvements in SRS technique with dose reduction, use of a single isocenter, and smaller collimators were made to reduce the incidence of this serious complication. Pallidotomies performed with radiosurgery did not achieve the same good results. Even though the development of DBS has supplanted lesioning as the first alternative in movement disorder surgery; SRS might still be the only treatment option for selected patients.

Gamma Knife Thalamotomy for Parkinson Disease and Essential Tremor: A Prospective Multicenter Study

BACKGROUND:

No prospective study of gamma knife thalamotomy for intractable tremor has previously been reported.

Objective:

To clarify the safety and optimally effective conditions for performing unilateral gamma knife (GK) thalamotomy for tremors of Parkinson disease (PD) and essential tremor (ET), a systematic postirradiation 24-month follow-up study was conducted at 6 institutions. We present the results of this multicenter collaborative trial.

Methods:

In total, 72 patients (PD characterized by tremor, n = 59; ET, n = 13) were registered at 6 Japanese institutions. Following our selective thalamotomy procedure, the lateral part of the ventralis intermedius nucleus, 45% of the thalamic length from the anterior tip, was selected as the GK isocenter. A single 130-Gy shot was applied using a 4-mm collimator. Evaluation included neurological examination, magnetic resonance imaging and/or computerized tomography, the unified Parkinson's disease rating scale (UPDRS), electromyography, medication change, and video observations.

Results:

Final clinical effects were favorable. Of 53 patients who completed 24 months of follow-up, 43 were evaluated as having excellent or good results (81.1%). UPDRS scores showed tremor improvement (parts II and III). Thalamic lesion size fluctuated but converged to either an almost spherical shape (65.6%), a sphere with streaking (23.4%), or an extended high-signal zone (10.9%). No permanent clinical complications were observed.

Conclusion:

GK thalamotomy is an alternative treatment for intractable tremors of PD as well as for ET. Less invasive intervention may be beneficial to patients.

Deep brain stimulation and frameless stereotactic radiosurgery in the treatment of bilateral parkinsonian tremor: target selection and case report of two patients

Considerable positive experience in functional radiosurgery has been reported since Leksell's first experience in 1951, but the development of frameless radiosurgery was been limited because of the difficulty of identifying invisible functional targets. In this paper we report on two cases of bilateral parkinsonian tremor successfully treated with DBS on one side and with frameless radiosurgery on the contralateral side. We focus on the methodology developed to define the three-dimensional target coordinates for frameless radiosurgery. Two patients suffering from a disabling upper-limb parkinsonian tremor underwent frameless radiosurgical thalamotomy. To accurately identify the treatment target the CT gantry was treated as a stereotactic frame; a rototranslation between the origin of the screen and the origin of the stereotactic atlas allowed us to obtain atlas-registered 3D coordinates of each point on the CT axial brain slices. Both patients achieved complete bilateral tremor control by unilateral radiosurgery and contralateral DBS. We developed a method for determining the 3D coordinates of a known functional target to treat with frameless radiosurgery. Based on the initial experiences, frameless radiosurgery appears to be an alternative treatment for Parkinsonian upper limb tremor in the presence of increased surgical risks for DBS placement.

Radiosurgery for movement disorders

Stereotactic radiosurgery (SRS) has been proposed as an alternative treatment modality to pharmaceutical administration and deep brain stimulation (DBS) for patients suffering from movement disorders. Advanced neuroimaging is required for the identification of the functional structures and the accurate placement of the SRS lesion within the brain. Atlas-based techniques have also been used to aid delineation of the target during treatment planning. Maximum doses greater than 120 Gy have been suggested for controlling movement disorders. These high delivered doses and the irreversible character of SRS require accurate placement of the created lesions. In this article, achievements in the field of stereotactic radiosurgery, neuroimaging, and radiosurgical dose planning are reviewed, and an overview is provided of the clinical experience obtained to date in the radiosurgical treatment of movement disorders.

Stereotactic body radiation therapy: the report of AAPM Task Group 101

Task Group 101 of the AAPM has prepared this report for medical physicists, clinicians, and therapists in order to outline the best practice guidelines for the external-beam radiation therapy technique referred to as stereotactic body radiation therapy (SBRT). The task group report includes a review of the literature to identify reported clinical findings and expected outcomes for this treatment modality. Information is provided for establishing a SBRT program, including protocols, equipment, resources, and QA procedures. Additionally, suggestions for developing consistent documentation for prescribing, reporting, and recording SBRT treatment delivery is provided.

Gamma knife radiosurgery for movement disorders: a concise review of the literature

Medication is the predominant method for the management of patients with movement disorders. However, there is a fraction of patients who experience limited relief from pharmaceuticals or experience bothersome side-effects of the drugs. Deep brain stimulation (DBS) and surgical lesioning of the thalamus and basal ganglia are respected neurosurgical procedures, with valued success rates and a very low incidence of complications. Despite these positive outcomes, DBS and surgical lesioning procedures are contraindicated for some patients. Stereotactic radiosurgery with the Gamma Knife (GK) has been used as a lesioning technique for patients seeking a non-invasive treatment alternative and for medication-intolerable patients, who are unable to undergo DBS or lesioning due to comorbid medical conditions. Tremors of various etiologies are treated using GK thalamotomy, which targets the ventralis intermedius nucleus. GK thalamotomy produces favorable outcomes when treating tremors, with success rates ranging from 80-100%. In contrast, GK pallidotomy targets the internal globus pallidus, and is used in treating bradykinesia, rigidity, and dyskinesia. Although radiosurgery has proven beneficial for tremors, radiosurgical pallidotomy for bradykinesia, rigidity, and dyskinesia remains questionable, with mixed success rates in the literature that ranges from 0-87%. We suggest that GK thalamotomy be offered along with other neurosurgical approaches as a feasible treatment option to patients who prefer the non-invasive nature of radiosurgery and to those who are unqualified candidates for the neurosurgical alternatives. Also, we advise that patients with bradykinesia, rigidity, and dyskinesia be educated about the variability in the literature pertaining to GK pallidotomy before proceeding with treatment.

Gamma Knife thalamotomy for treatment of essential tremor: long-term results

Object

The goal of this report was to describe the safety and effectiveness of nucleus ventralis intermedius (VIM) thalamotomy performed with the Leksell Gamma Knife (GK) for the treatment of essential tremor (ET).

Methods

One hundred seventy-two patients underwent a total of 214 VIM thalamotomy procedures with the Leksell GK between February 1994 and March 2007 for treatment of disabling ET. Eleven patients were lost to follow-up less than 1 year after the procedures, so that in this report the authors describe the results in 161 patients who underwent a total of 203 thalamotomies (119 unilateral and 42 bilateral).

Results

There were statistically significant decreases (p < 0.0001) in tremor scores for both writing and drawing. The mean postoperative follow-up duration for all patients was 44 ± 33 months. Fifty-four patients have been followed for more than 60 months posttreatment. There were 14 patients who suffered neurological side effects that were temporary (6) or permanent (8), which accounted for 6.9% of the 203 treatments. All complications were related to lesions that grew larger than expected.

Conclusions

A VIM thalamotomy with the Leksell GK offers a safe and effective alternative for surgical treatment of ET. It is particularly applicable to patients who are not ideal candidates for deep brain stimulation but can be offered to all patients who are considering surgical intervention for ET.

Gamma knife radiosurgery for essential tremor: a case report and review of the literature

Approximately 5 million people in America are affected by essential tremors (ET), which are classified as a type of benign movement disorder. This disease manifests as tremors that usually occur in the hands, but they may also be present in the head, face, tongue, and lower limbs. Radiofrequency thalamotomy (RF) and deep brain stimulation (DBS) are common invasive procedures with proven track records that are used to treat ET. Although these procedures have high success rates, they still put patients at risk of potential side effects and are invasive by nature. Thalamotomy using the gamma knife (GK) also produces favorable outcomes in treating tremors, without the complications associated with invasive neurosurgery procedures. This report describes the presenting symptoms and extended treatment outcome for a patient with an advanced case of ET, who received GK thalamotomy treatment six years ago. Because of this non-invasive treatment, she regained the ability to paint and live with an improved quality of life. We also discuss and review the relevant literature regarding the risks and benefits of this treatment modality. GK thalamotomy is one effective option for the treatment of ET, and due to its noninvasive nature, it has a different risk profile than neurosurgery. We suggest that GK thalamotomy should be presented as one viable treatment option to all ET patients, and should be recommended to those who would be best served by less invasive treatment techniques.

Assessing neurotoxicity from the low-dose radiation component of radiosurgery using magnetic resonance spectroscopy

The aim of the study was to determine if biochemical changes indicative of injury, assessed using magnetic resonance spectroscopic imaging (SI), are observed after stereotactic radiosurgery (SRS). The study included patients who underwent SI immediately before and 1, 30, and 90 days following SRS. Short TE spectra (TR/TE 1000/35 ms) were acquired at the SRS isocenter with a 2D PRESS-CSI sequence on a single 1.5 T scanner. The SRS isodose lines were overlaid on the magnetic resonance imaging slice utilized for SI data acquisition. N-Acetyl aspartate (NAA)/creatine (Cr) and choline (Cho)/Cr ratios were computed for multiple voxels located between the 25 and 50 cGy isodose lines (low dose) and the 200 and 350 cGy isodose lines (medium dose). An analysis of variance and paired t-tests compared metabolite levels at different time points. Twelve patients were enrolled, although 3 were excluded secondary to poor spectral data quality or deviations from the prescribed SI protocol. The median number of voxels analyzed from the low- and medium-dose region was 7 and 4, respectively. No significant changes in metabolite peak height ratios over time were seen in the low-dose region, for either NAA/Cr (P = .89) or Cho/Cr (P = .85). There was no difference in Cho/Cr peak height ratios in the medium-dose region (P = .62). There was an increase in the NAA/Cr peak height ratio in the medium-dose region between day -1 and day +30 (P = .003), followed by a decline to baseline between days +30 and +90 (P = .03). We did not observe a significant decline in NAA/Cr or change in Cho/Cr peak heights in uninvolved brain parenchyma after SRS.

THE APPLICATION OF STEREOTACTIC RADIOSURGERY TO DISORDERS OF THE BRAIN

STEREOTACTIC RADIOSURGERY IS the first widely used “biological surgery.” The opportunity for surgeons working with radiation oncologists and medical physicists to affect cell structures with both direct and indirect vascular effects has transformed neurosurgery. As a minimal access surgical approach, it fits well into the patient goals of functional preservation, risk reduction, and cost-effectiveness. Longer-term results have been published for many indications. For many disorders, it may be better to “leave the tumor in rather than take it out.” Radiosurgery has had an impact on the management of patients with vascular malformations, all forms of cerebral neoplasia, and selected functional disorders such as trigeminal neuralgia and tremor. It can be performed alone when lesion volume is not excessive or as part of a multimodality strategy with resection or endovascular surgery. Epilepsy, behavioral disorders, and other novel indications are the topics of current investigation. The combination of high-resolution imaging, high-speed computer workstations, robotics, patient fixation techniques, and radiobiological research has put radiosurgery into the practice of almost all neurosurgeons.

Gamma Knife thalamotomy for essential tremor

Object

The purpose of this study was to evaluate the results following Gamma Knife thalamotomy (GKT) for medically refractory essential tremor in a series of patients in whom open surgical techniques were not desirable.

Methods

Thirty-one patients underwent GKT for disabling essential tremor after medical therapy had failed. Their mean age was 77 years. Most patients were elderly or had concomitant medical illnesses. A single 4-mm isocenter was used to target a maximum dose of 130 or 140 Gy to the nucleus ventralis intermedius. Items from the Fahn-Tolosa-Marin clinical tremor rating scale were used to grade tremor and handwriting before and after radiosurgery.

Results

The median follow-up was 36 months. In the group of 26 evaluable patients, the mean tremor score (± standard deviation) was 3.7 ± 0.1 preoperatively and 1.7 ± 0.3 after radiosurgery (p < 0.000015). The mean handwriting score was 2.8 ± 0.2 before GKT and 1.7 ± 0.2 afterward (p < 0.0002). After radiosurgery, 18 patients (69%) showed improvement in both action tremor and writing scores, 6 (23%) only in action tremor scores, and 3 (12%) in neither tremor nor writing. Permanent mild right hemiparesis and speech impairment developed in 1 patient 6 months after radiosurgery. Another patient had transient mild right hemiparesis and dysphagia.

Conclusions

Gamma Knife thalamotomy is a safe and effective therapy for medically refractory essential tremor. Its use is especially valuable for patients ineligible for radiofrequency thalamotomy or deep brain stimulation. Patients must be counseled on potential complications, including the low probability of a delayed neurological deficit.

The role of radiosurgery in the management of malignant brain tumors

Stereotactic radiosurgery (SRS) provides the means for creating lesions in deep-seated areas of the brain inaccessible to invasive surgery, using single high doses of focused ionizing radiation, administered using stereotactic guidance. It is a surgical technique designed to produce a specific radiobiological effect within a sharply defined target region in a single treatment session. Its technical application requires a stereotactic coordinate system, highly accurate patient repositioning (usually fixed), and multiple convergent beams of photon radiation. SRS appears to provide no benefit in the upfront treatment of newly diagnosed malignant gliomas but may be used to effectively palliate small well-demarcated volumes of recurrent disease. For selected patients with brain metastases treated with whole-brain radiation therapy (WBRT), the addition of SRS improves median survival. In selected patients with brain metastases, it is also rational to withhold WBRT in favor of radiosurgery alone, with WBRT reserved for salvage without a decrease in median survival time.

Neurophysiological Evaluation of the Optimum Target in Gamma Thalamotomy: Indirect Evidence

Gamma thalamotomy has been useful for the treatment of Parkinson's disease and other movement disorders, but it has disadvantages, such as a delayed clinical effect after irradiation and the inaccuracy of targeting because depth recording is not available. Therefore, we sought to determine the optimum target in gamma thalamotomy based on the results of conventional selective thalamotomy with reference to the AC-PC line. To obtain indirect support for the appropriateness of the optimum target, we performed depth recording around the region of the estimated optimum target based on the results of conventional thalamotomy. Four patients with tremor caused by Parkinson's disease or essential tremor were used as subjects after they gave their fully informed consent. The targets were determined as points 6-8 mm anterior to the posterior commissure, 4-6 mm dorsal to the level of the intercommissural line, and 15-17 mm lateral from the midline. Rhythmic discharge time-locked to tremor and/or kinesthetic neurons were found within the expected target area in all patients. Finally, in all cases, the tremor was abolished without complications after coagulative lesions were made with dual coagulation needles to cover the supposed Vim zone according to the depth recording. We considered that the target point determined in the same way as in gamma thalamotomy is suitable from an anatomophysiological perspective.

A critical review of the clinical effects of therapeutic irradiation damage to the brain: the roots of controversy

We critically examined the damaging affects of therapeutic irradiation by comparing results from cross-disciplinary studies of early- and late-delayed radiotherapy effects. Focus is attained by concentrating on clinical treatment issues (volume of brain, dose, timing of effects, age, modality types, and stereotactic treatment techniques), rather than on methodological means or problems, which is necessary to understand the mechanisms and characteristics of radiotherapy-induced behavioral dysfunction including cognition. We make observations and hypotheses about the actual risks from radiotherapy that could be informative in the treatment decision process, and which may lessen the concerns of some patients and their families about the risks they take when receiving radiation. Conditions that predispose to radiation injury are reviewed: (1) higher doses even to part of the brain versus lower doses to the whole brain, (2) combined treatment modalities, (3) malignancy itself, (4) radiation early during postnatal brain development, and (5) late-delayed effects (more than 3 years posttreatment). Current neurocognitive frameworks for understanding cognitive change over time in children and adults are summarized, along with the literature on effects of brain tumors and treatment on depression. No studies have as yet identified candidate brain regions that are more sensitive to radiotherapy. Two studies have provided early, preliminary evidence for a specific vulnerability of visual attention/memory to the early stage of late radiation damage. Furthermore, radiation effects appear severe only in a minority of patients. Risk is related to direct and indirect effects of cancer type, concurrent clinical factors, and premorbid risk factors.

Linear accelerator thalamotomy

BACKGROUND

The capability of performing functional radiosurgery lesions in the brain using a dedicated linear accelerator (LINAC) have not yet been demonstrated. This study evaluates modern LINAC technology for the creation of a sharp, small and functionally eloquent lesion in the thalamus.

METHODS

Three patients underwent thalamotomy using a dedicated linear accelerator to radiosurgery, 2 females and 1 male, ages were 52, 53, and 73 years. Two patients presented with unilateral poststroke central pain and 1 with unilateral upper extremity pain secondary to metastatic infiltration of the brachial plexus. Maximal doses varied from 150 to 200 Gy, delivered by a 5-mm diameter collimator and 5 to 8 noncoplanar arcs evenly distributed.

RESULTS

All patients gained substantial relief of their pain. They were able to reduce their medications and improve their activity levels. The patient with end-stage metastatic disease died of his malignancy 2 weeks after the treatment. One patient presented with recurrence of the pain 4 months after the treatment. No clinical complications were noticed.

CONCLUSIONS

A dedicated linear accelerator is able to perform a precise and circumscribed lesion in the thalamus for pain control. Moreover, it proved to be safe, because no complications were observed. For patients using chronic anticoagulant therapy or with severe disabilities caused by cardiac, pulmonary or malignant diseases, this technique represents an alternative of treatment to radiofrequency thalamotomy.

Lesion therapy for Parkinson's disease and other movement disorders: Update and controversies

An analysis of the international literature on lesioning for movement disorders was undertaken to review lesion therapy for Parkinson's disease (PD) and other movement disorders and to highlight important controversies surrounding this surgical technique. Lesions have been placed throughout the neuraxis with varying approaches and success. Our understanding of the pathophysiological basis underlying the development of PD and other movement disorders has led to a better understanding of why lesioning certain portions of the nervous system should improve motor function. Advances in imaging technology and electrophysiological techniques used for localization of brain structures, such as microelectrode mapping, have improved the ability to accurately identify and lesion target structures deep in the brain. This improvement has led to an increase in the degree and consistency of clinical benefit. The major controversies in lesion therapy include: (1) which target for which disorder; (2) determination of the optimal lesion site and whether the external globus pallidus (GPe) should be included in the pallidotomy lesion for PD; (3) determination of the size of the lesion; (4) whether bilateral lesions can be placed without the high incidence of side effects reported by some investigators; (5) whether microelectrodes aid in the ability to improve clinical outcomes or increase the risk of side effects by making multiple microelectrode penetrations; (6) whether the subthalamic nucleus (STN) should be explored further as a lesioning target; and (7) whether lesioning should be abandoned entirely in favor of deep brain stimulation (DBS). Many important questions and controversies regarding lesion therapy remain unanswered. It is unlikely given the pro-DBS environment that these questions will be answered in the near future. We should, however, be careful not to abandon an effective therapy before fully exploring through randomized trials the relative effect of different surgical approaches for the treatment of patients with movement disorders.

Gamma knife subthalamotomy for Parkinson disease: the subthalamic nucleus as a new radiosurgical target

✓ The authors present the neuroimaging, treatment planning, and radiosurgical technique for the first reported case of unilateral radiosurgical subthalamotomy, which was performed to control motor symptoms associated with advanced Parkinson disease (PD) in a patient who had undergone previous contralateral radiofrequency (RF) pallidotomy.

A 73-year-old woman with end-stage PD had undergone RF pallidotomy of the right globus pallidus with resolution of symptoms. Two years following this procedure, due to the natural progression of her disease, she suffered recurrent motor fluctuations, dyskinesia, and worsening bradykinesia of the right side. Her Parkinson's Disease Disability Rating (PDDR) score was 28. Computerized tomography and magnetic resonance (MR) imaging were used to localize the left subthalamic nucleus (STN). The patient underwent gamma knife radiosurgery—a single shot of 120 Gy was administered using the 4-mm collimator helmet.

The patient was evaluated up to 42 months after the procedure. The dyskinesia became minimal. Right-sided motor control improved as did her balance. At 3 months after treatment MR imaging demonstrated the radiosurgical lesion in the left STN. At 3.5 years postradiosurgery, she experienced minimal focal (oral) dyskinesia, no bradykinesia or rigidity, and her PDDR score was 11.

Radiosurgery of the STN in this case was safe and effective. The STN is a readily localized anatomical target with neuroimaging. Radiosurgery avoids the risks of open procedures.

Thalamic lesions produced by gamma thalamotomy for movement disorders

Object. The treatment of Parkinson disease and other kinds of involuntary movement by gamma knife radiosurgery (GKS) is presented. This is an extension of previous work. The clinical course and thalamic lesions were the main factors examined.

Methods. Seventeen new cases were added to the previously reported 36 cases. The course and results for the whole series of 53 patients were examined. Treatment was undertaken using a single 4-mm collimator shot to deliver 130 Gy to the target. The target was determined in the previously treated patients by using classic methods involved in conventional stereotactic thalamotomy with microrecording. More recently, target localization has been performed by relating the target point to the total length of the thalamus. Points may then be defined as percentages of that length measured from the anterior pole. Targets can then be determined in relationship to the appropriate percentage.

Thirty-five patients have been followed for more than 2 years and the longest follow up was 8 years. Two kinds of thalamic lesion were seen after GKS. Volumetric analysis on MR imaging revealed that the larger lesion was 400 to 500 mm3 at the beginning and gradually decreased in size. The smaller lesion occupied approximately 200 mm3 and also shrank over several months. Eighty percent of the treated cases showed good results and no significant complications, with the tremor subsiding at 1 year (Type 1). Several cases deviated from this standard course in four different ways (Types 2–5). If tremor persisted, conventional stereotactic thalamotomy with microrecording was performed. During such operations, normal neuronal activity was recorded from the region adjacent to the GKS thalamotomy target. This was the region showing a high signal on MR imaging. The activity patterns included the rhythmical grouped discharge of tremor rhythm.

Conclusions. Gamma thalamotomy for functional disorders is still under development, but because the results with careful target planning are satisfactory, there are grounds for increasing optimism.

Radiosurgery performed with the aid of a 3-mm collimator in the subthalamic nucleus and substantia nigra of the vervet monkey

OBJECT

Radiosurgery for functional neurosurgery performed using a linear accelerator (LINAC) has not been extensively characterized in preclinical studies. In the present study, the properties of a newly designed 3-mm-diameter collimator were evaluated in a dedicated LINAC, which produced lesions in the basal ganglia of vervet monkeys. Lesion formation was determined in vivo in three animals by examining magnetic resonance (MR) images to show the dose-delivery precision of targeting and the geometry and extent of the lesions. Postmortem immunohistochemical studies were conducted to determine the extent of lesion-induced radiobiological effects.

METHODS

In three male vervet monkeys, the subthalamic nucleus (STN; one animal) and the pars compacta of the lateral substantia nigra (SN; two animals) were targeted by a Novalis Shaped Beam Surgery System that included a 3-mm collimator and delivered a maximum dose of 150 Gy. Magnetic resonance images obtained 4, 5, and 9 months posttreatment were reviewed, and the animals were killed so that immunohistological characterizations could be made.

CONCLUSIONS

The generation of precise radiosurgical lesions by a 3-mm collimator was validated in studies that targeted the basal ganglia of the vervet monkey. The extent of the lesions created in all animals remained restricted in diameter (< 3 mm) throughout the duration of the studies, as assessed by reviewing MR images. Histological studies showed that the lesions were contained within the STN and SN target areas and that there were persistent increases in glial fibrillary acidic protein immunoreactivity. Increases in immunoreactivity for tyrosine hydroxylase, the serotonin transporter, and the GluR1 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate glutamate receptor in penumbral regions of the lesion were suggestive of compensatory neuronal adaptations. This radiosurgical approach may be of particular interest for the induction of lesions of the STN and SN in studies of experimental parkinsonism, as well as for the development of potential radiosurgical treatments for Parkinson disease.

Emergence of complex, involuntary movements after gamma knife radiosurgery for essential tremor

Gamma knife radiosurgery is generally considered a safer alternative to traditional pallidotomy or thalamotomy. We report the case of a 59-year-old patient with essential tremor who developed a complex, disabling movement disorder following gamma knife thalamotomy. This case illustrates the need for long-term follow-up to fully evaluate the potential for complications following radiosurgery.

Gamma knife thalamotomy for treatment of tremor: long-term results

Object. The purpose of this study was to investigate the long-term effects of gamma knife thalamotomy for treatment of disabling tremor.

Methods. One hundred fifty-eight patients underwent magnetic resonance imaging—guided radiosurgical nucleus ventralis intermedius (VIM) thalamotomy for the treatment of parkinsonian tremor (102 patients), essential tremor (52 patients), or tremor due to stroke, encephalitis, or cerebral trauma (four patients). Preoperative and postoperative blinded assessments were performed by a team of independent examiners skilled in the evolution of movement disorders. A single isocenter exposure with the 4-mm collimator helmet of the Leksell gamma knife unit was used to make the lesions.

In patients with Parkinson's disease 88.3% became fully or nearly tremor free, with a mean follow up of 52.5 months. Statistically significant improvements were seen in Unified Parkinson's Disease Rating Scale tremor scores and rigidity scores, and these improvements were maintained in 74 patients followed 4 years or longer.

In patients with essential tremor, 92.1% were fully or nearly tremor free postoperatively, but only 88.2% remained tremor free by 4 years or more post-GKS. Statistically significant improvements were seen in the Clinical Rating Scale for tremor in essential tremor patients and these improvements were well maintained in the 17 patients, followed 4 years or longer. Only 50% of patients with tremor of other origins improved significantly.

One patient sustained a transient complication and two patients sustained mild permanent side effects from the treatments.

Conclusions. Gamma knife VIM thalamotomy provides relief from tremor equivalent to that provided by radiofrequency thalamotomy or deep brain stimulation, but it is safer than either of these alternatives. Long-term follow up indicates that relief of tremor is well maintained. No long-term radiation-induced complications have been observed.

Evaluation of gamma thalamotomy for parkinsonian and other tremors: survival of neurons adjacent to the thalamic lesion after gamma thalamotomy

Object. The effects of gamma thalamotomy for parkinsonian and other kinds of tremor were evaluated.

Methods. Thirty-six thalamotomies were performed in 31 patients by using a 4-mm collimator. The maximum dose was 150 Gy in the initial six cases, which was reduced to 130 Gy thereafter. The longest follow-up period was 6 years. The target was determined on T2-weighted and proton magnetic resonance (MR) images. The point chosen was in the lateral-most part of the thalamic ventralis intermedius nucleus. This is in keeping with open thalamotomy as practiced at the authors' institution. In 15 cases, gamma thalamotomy was the first surgical procedure. In other cases, previous therapeutic or vascular lesions were visible to facilitate targeting.

Two types of tissue reaction were onserved on MR imaging: a simple oval shape and a complex irregular shape. Neither of these changes affected the clinical course. In the majority of cases, the tremor subsided after a latent interval of approximately 1 year after irradiation. The earliest response was demonstrated at 3 months. In five cases the tremor remained. In four of these cases, a second radiation session was administered. One of these four patients as well as another patient with an unsatisfactory result underwent open thalamotomy with microrecording. In both cases, depth recording adjacent to the necrotic area revealed normal neuronal activity, including the rhythmic discharge of tremor. Minor coagulation was performed and resulted in immediate and complete arrest of the remaining tremor.

Conclusions. Gamma thalamotomy for Parkinson's disease seems to be an alternative useful method in selected cases.

The surgical treatment of Parkinson's disease

Surgical treatment of Parkinson's disease (PD) can provide gratifying symptomatic improvements for many individuals who suffer from persistent disabling symptoms despite the best available medical management. Current surgical therapies include ablative techniques (thalamotomy and pallidotomy), augmentative techniques (nondestructive) (deep brain stimulation), and restorative techniques (tissue transplantation and gene therapy). Ablative procedures can provide substantial clinical benefit, but the current trend is toward deep brain stimulation, which can provide similar symptomatic improvement in a nondestructive manner. Restorative techniques, such as tissue transplantation and gene therapy, are exciting but have significant obstacles to overcome before their promise can be realized. Until the underlying pathological defect of PD can be identified and treated, surgical intervention is likely to remain important in the symptomatic treatment of this disabling disease.

Neuroprotective "agents" in surgery. Secret "agent" man, or common "agent" machine?

The search for clinically-effective neuroprotective agents has received enormous support in recent years--an estimated $200 million by pharmaceutical companies on clinical trials for traumatic brain injury alone. At the same time, the pathophysiology of brain injury has proved increasingly complex, rendering the likelihood of a single agent "magic bullet" even more remote. On the other hand, great progress continues with technology that makes surgery less invasive and less risky. One example is the application of endovascular techniques to treat coronary artery stenosis, where both the invasiveness of sternotomy and the significant neurological complication rate (due to microemboli showering the cerebral vasculature) can be eliminated. In this paper we review aspects of intraoperative neuroprotection both present and future. Explanations for the slow progress on pharmacologic neuroprotection during surgery are presented. Examples of technical advances that have had great impact on neuroprotection during surgery are given both from coronary artery stenosis surgery and from surgery for Parkinson's disease. To date, the progress in neuroprotection resulting from such technical advances is an order of magnitude greater than that resulting from pharmacologic agents used during surgery. The progress over the last 20 years in guidance during surgery (CT and MRI image-guidance) and in surgical access (endoscopic and endovascular techniques) will soon be complemented by advances in our ability to evaluate biological tissue intraoperatively in real-time. As an example of such technology, the NASA Smart Probe project is considered. In the long run (i.e., in 10 years or more), pharmacologic "agents" aimed at the complex pathophysiology of nervous system injury in man will be the key to true intraoperative neuroprotection. In the near term, however, it is more likely that mundane "agents" based on computers, microsensors, and microeffectors will be the major impetus to improved intraoperative neuroprotection.

Radiosurgery: where we were, are, and may be in the third millennium

Radiosurgery will celebrate its Golden Jubilee in the year 2001. More than 100,000 patients throughout the world have undergone radiosurgery since Lars Leksell first described the technique in 1951. Rapid developments in neuroimaging and even robotic technology in the past decade have contributed to improved outcomes and wider applications for radiosurgery. A variety of different radiosurgical techniques have been developed in the past two decades. Numerous studies have examined the benefits and risks of radiosurgery performed with various devices. The long-term results of radiosurgery are now available, and these results have established radiosurgery as an effective noninvasive treatment method for intracranial vascular malformations and many tumors. Additional applications of radiosurgery for the treatment of malignant tumors and functional disorders are being assessed. Radiosurgery is an impressive combination of minimally invasive technologies administered by a multidisciplinary team of surgeons, oncologists, medical physicists, and engineers.

Microelectrode-guided thalamotomy for Parkinson's disease

OBJECTIVE

To describe the outcomes in our first 40 microelectrode-guided thalamotomies for parkinsonian tremor.

METHODS

Twenty-four left-sided and 16 right-sided thalamotomies were performed between October 1984 and January 1996; the mean follow-up period was 35.8 months (range, 1-152 mo). The results were evaluated retrospectively and semiquantitatively by a disinterested observer (MNL) and correlated with the quality of the microelectrode recording and the number and size of radiofrequency lesions made. The first 20 and second 20 procedures were evaluated separately.

RESULTS

At the last follow-up, the Unified Parkinson's Disease Rating Scale showed no or virtually no tremor in the upper limb in 75% of patients or in the lower limb in 73% of patients. No significant persistent complications were found. These results were achieved at the expense of having to repeat the procedure on 11 sides (in 5 because of technical problems and in 6 for no obvious reason). Total or nearly total abolition of tremor occurred after the first procedure in 40% of the first 20 operations and in 65% of the second 20. Eight of the first 20 procedures and 2 of the second 20 failed for technical reasons. Lesions were made larger in the second 20 procedures than in the first 20. With the use of an electrode with a 1.1 x 3-mm bare tip for 60 seconds, it seems that lesions had to be created at 60 degrees C or more to produce a successful result.

CONCLUSION

Thalamotomy with microelectrode recording is an effective procedure with which to treat tremor in patients with Parkinson's disease and may involve fewer complications than conventional techniques. The procedure appears to involve a learning curve.

Evaluation of the spatial accuracy of magnetic resonance imaging-based stereotactic target localization for gamma knife radiosurgery of functional disorders

PURPOSE

This study was undertaken to determine the impact of geometric distortions on the spatial accuracy of magnetic resonance imaging (MRI)-guided stereotactic localization for gamma knife functional radiosurgery.

METHOD

The spatial accuracy of MRI was evaluated by comparing stereotactic coordinates of intracranial targets, external fiducials, and anatomic structures defined by computed tomographic and MRI studies of the Radionics skull phantom (Radionics, Inc., Burlington, MA), the Rando head phantom, and 11 patients who underwent gamma knife functional radiosurgery. The distortion in MRI was assessed from computed tomographic and MRI fusion studies for these patients, as well as from MRI studies acquired by swapping the direction of the magnetic field gradients for five patients who underwent gamma knife radiosurgery and three patients who underwent MRI-guided frameless surgery. A follow-up program to compare the location of the created lesion with the intended target complemented the analysis.

RESULTS

The average difference between computed tomographic and MRI stereotactic coordinates of external fiducials, intracranial targets, and anatomic landmarks was of the order of 1 pixel size (0.9 x 0.9 x 1 mm3) along the x, y, and z axes. The average linear scaling along these axes as determined by fusion studies was approximately 0.8% and consistent with a single pixel. The follow-up studies, available for seven patients, revealed good agreement between the location of the created lesion and the intended target.

CONCLUSION

The spatial accuracy of an MRI-based localization system can be comparable to computed tomography-based localization with the added benefit of MRI resolution. Both machine- and object-related MRI distortions can be reduced to an acceptable level with contemporary scanners, optimized scanning sequences, and distortion-resistant stereotactic instruments.

An accurate adjustable applicator for magnetic resonance imaging-based stereotactic procedure using the Leksell G frame

OBJECTIVE

An applicator system for the Leksell G frame was constructed to enable accurate placement of the frame for stereotactic magnetic resonance imaging (MRI) and successful stereotactic surgery. The applicator prevents inaccurate placement of the fiducial box on the patient's head and prevents contact of the frame holder with the patient's shoulder while in the MRI unit. It also helps to ensure optimal positioning of desired targets within the three-dimensional stereotactic space defined by the frame.

METHODS

The applicator is made of transparent acrylic plates, which simulate the fiducial box that is attached to the frame for the preoperative stereotactic MRI study. An air cuff at the top supports the frame at any desired height and makes minute adjustments possible. Side cuffs help to keep the frame at the desired position from right to left. Indicators attached to the frame for the anterior fiducial plate prevent potential contact of the plate with the anterior posts and help avoid a poor fit caused by bending of the frame from excessive torque on the cranium fixation screws. Indicators for the MRI frame holder on the foot screws predict potential collision of the holder with the patient's shoulder before actually applying the holder on the frame. The applicator shows the range and limits of the Leksell stereotactic arc.

RESULTS

This applicator system has been used effectively in more than 89 MRI-based functional stereotactic procedures. These include pallidotomy, thalamotomy, implantation of deep brain stimulators, and implantation of depth electrodes. It has functioned well and has facilitated excellent operative results in these cases.

CONCLUSION

This simple frame applicator eliminates the need for reapplication of the stereotactic frame and additional imaging studies, thus providing successful and appropriate frame placement for stereotactic surgery.

Radiation therapy for benign central nervous system disease

The most common indication for the use of radiation therapy in the treatment of benign central nervous system disease is for the treatment of benign brain tumors, such as meningioma, pituitary adenoma, acoustic neuroma, arteriovenous malformation, and craniopharyngioma. Other less common benign intracranial tumors treated with radiation include chordoma, pilocytic astrocytoma, pineocytoma, choroid-plexus papilloma, hemangioblastoma, and temporal bone chemodectomas. Benign conditions, such as histiocytosis X, trigeminal neuralgia, and epilepsy, are also amenable to radiation treatment. There have also been reports of radiosurgery being used for the treatment of movement disorders and psychiatric disturbances, such as obsessive-compulsive and anxiety disorders. For benign brain tumors, radiation therapy as either primary or adjuvant therapy plays an integral role in improving local control. In the treatment of trigeminal neuralgia, epilepsy, tremor, and some psychiatric disturbances, radiosurgery may help ameliorate or eliminate some symptoms. Patients with benign central nervous system disease are expected to live a long time. As such, treatment should be highly conformal and based on three-dimensional planning using magnetic resonance imaging, computed tomography, or both. It is critical that damage to normal brain be minimized.