Stereotactic Imaging Research Articles

Magnetic Resonance Imaging-Guided Focused Laser Interstitial Thermal Therapy for Subinsular Metastatic Adenocarcinoma

To describe the novel use of the AutoLITT System (Monteris Medical, Winnipeg, Manitoba, Canada) for focused laser interstitial thermal therapy (LITT) with intraoperative magnetic resonance imaging (MRI) and stereotactic image guidance for the treatment of metastatic adenocarcinoma in the left insula. The patient was a 61-year-old right-handed man with a history of metastatic adenocarcinoma of the colon. He had previously undergone resection of multiple lesions, Gamma Knife radiosurgery, and whole-brain radiation. Despite treatment of a left insular tumor, serial imaging revealed that the lesion continued to enlarge. Given the refractory nature of this tumor to radiation and the deep-seated location, the patient elected to undergo LITT treatment. The center of the lesion and entry point on the scalp were identified with STEALTH (Medtronic, Memphis, Tennessee) image-guided navigation. The AXiiiS Stereotactic Miniframe (Monteris Medical) for the LITT system was secured onto the skull, and a trajectory was defined to achieve access to the centroid of the tumor. After a burr hole was made, a gadolinium template probe was inserted into the AXiiiS base. The trajectory was confirmed via an intraoperative MRI, and the LITT probe driver was attached to the base and CO2-cooled, side-firing laser LITT probe. The laser was activated and thermometry images were obtained. Two trajectories, posteromedial and anterolateral, produced satisfactory tumor ablation. LITT with intraoperative MRI and stereotactic image guidance is a newly available, minimally invasive, and therapeutically viable technique for the treatment of deep seated brain tumors.

11C‐methionine uptake and intraoperative 5‐aminolevulinic acid‐induced fluorescence as separate index markers of cell density in glioma

The extent of tumor resection is acknowledged as 1 of the prognostic factors for glioma. 5-Aminolevulinic acid (5-ALA)-induced fluorescence guidance and neuronavigation integrated with (11) C-methionine positron emission tomography (PET) are widely utilized under the expectation of improving the extent of resection. These 2 novel approaches are beneficial for glioma resections, and the combination of these approaches appears rational. However, biological characteristics reflecting 5-ALA-induced fluorescence and (11) C-methionine uptake have not been clearly elucidated, and studies about the relationship between 5-ALA-induced fluorescence and (11) C-methionine uptake have been limited. The present study aimed to clarify this issue. Data from 11 consecutive patients harboring astrocytic tumors were analyzed: 2 grade II and 2 grade III, and 7 grade IV tumors were included. Thirty samples from these patients were obtained from the relative periphery of each tumor. Relationships among histology, 5-ALA-induced fluorescence and (11) C-methionine uptake were analyzed by stereotactic sampling and image analysis. Uptake of (11) C-methionine correlated with cell density (R(2) = 0.322, P = .0059). Cell density was higher in fluorescence-positive areas than in negative areas (2760 ± 1080 vs 1450 ± 1380/mm(2) , P = .0132). Although both (11) C-methionine uptake and fluorescence seemed to correlate with cell density, no significant difference in (11) C-methionine uptake was seen between fluorescence-positive and -negative areas (P = .367). Multiple linear regression analysis revealed (11) C-methionine uptake and 5-ALA-induced fluorescence as independent indices for tumor cell density. These results indicate that 5-ALA fluorescence and (11) C-methionine PET image are separate index markers for cytoreduction surgery of gliomas.

Editorial: Brain tumors

For over a century physicians have tried to use what they see under the microscope to predict the behavior of brain tumors and to determine which treatment strategies would best benefit their patients. This approach has been particularly frustrating in pediatric neurooncology. What appears to be the same tumor in an infant may behave quite differently in an older child. That “same tumor” may have a very different prognosis in one anatomical location compared to another. A commonality in most pediatric brain tumor patients remains that what we accomplish as neurosurgeons in our attempts to remove a child’s tumor is presently the most important factor in that child’s prognosis. For most pediatric brain tumors, the difference between a grosstotal resection and a subtotal resection doubles the child’s chances of survival. As such, advances in neuroimaging and image-guided surgery are among the greatest adjuncts to surgery. The application of frameless stereotactic image guidance, functional neuroimaging, intraoperative MR imaging, early postoperative MR imaging, and second-look surgery has allowed the neurosurgeon to be more aggressive. This is evidenced by the fact that the number of children enrolled in national clinical trials with no or minimal residual tumor on their MR imaging has nearly doubled over the last 2 decades. Another major advance has been the routine banking of tumor tissue. This resource, coupled with more readily available molecular profiling techniques, has allowed us to understand that two ependymomas that look the same histologically are not the same tumor in the spinal cord as in the posterior fossa or the supratentorial space.8 The understanding of the molecular events giving rise to these tumors has allowed us to develop animal and in vitro models that are both histologically and molecularly the same as those in the human condition.4 The same holds true for small round blue-cell tumors. The recognition that molecular alterations in the INI-1 gene are associated with atypical teratoid rhabdoid tumors was a seminal occurrence.7 We now recognize that what we once called a medulloblastoma is one of several tumor subtypes.1 The Wnt-positive tumors, recognized by nuclear staining for b-catenin, are more likely to arise in younger children, are more likely to be located within the fourth ventricle, and in our last treatment trial were associated with 100% progression-free survival.2 Efforts are now underway to reduce the toxic side effects of treatment in this subgroup of children. Medulloblastomas associated with Sonic hedgehog (Shh) signaling abnormalities arise from a different cancer stem cell, are more likely to be located in the cerebellar hemisphere, and are more likely to be noted in infants and older children.3 With the development of GDC-0449, a specific Shh inhibitor, we now have targeted therapy for children with those medulloblastoma subtypes. For children with c-myc amplification or with large-cell anaplastic medulloblastomas, the prognosis remains dismal and we must develop novel targeted therapies for those children.5 In low-grade astrocytomas, similar progress has been made. The identification of BRAF abnormalities in pilocytic astrocytomas, the recognition that subependymal giant cell tumors respond quite nicely to mTOR inhibitors, and that antiangiogenesis agents such as bevacizumab offer specific molecular targets for treatment in these tumors, is further evidence that the understanding of the molecular pathways involved in tumor formation is our future. In this paper6 by Dr. Pollack, a pediatric neurosurgeon who has dedicated his life to better understanding childhood brain tumors, a very clear and readable overview of the progress made in the management of a variety of childhood brain tumors has been provided. A number of truths can be gleaned from the article. First, given the molecular studies that are available for these tumors, it behooves us at surgery not only to provide tissue for histology but also to bank fresh tumor tissue for future reference in each case. Second, children and their families should be offered enrollment in prospective clinical 133 134

Detection of brain micrometastases by high-resolution stereotactic magnetic resonance imaging and its impact on the timing of and risk for distant recurrences

The aim of this study was to assess the order of micrometastases that can be detected with high-resolution MR imaging at the time of Gamma Knife surgery (GKS), and to estimate the impact this has on the time until and incidence of distant recurrences. A consecutive series of 835 patients with brain metastases treated with GKS in a 7-year period, excluding patients in whom earlier brain metastases were treated with other modalities, were retrospectively analyzed. In all patients GKS was based on high Gd-dose (0.3 mmol/kg), high-resolution stereotactic MR imaging. These images were compared with the standard pretreatment MR images, and the difference in number of metastases found was analyzed. The distant recurrence rate following GKS was compared with that found in a prospective randomized study (Aoyama et al.) comparing radiosurgery to radiosurgery plus prophylactic whole-brain radiation therapy. New tumors were diagnosed in 40% (95% CI 36%-43%) of all patients as well as in the majority of patients with multiple lesions found on the diagnostic scan. The more tumors there were on the diagnostic scan, the higher the likelihood of detecting additional lesions with high-resolution imaging. It was calculated that approximately 50% of the micrometastases present at the time of GKS could be diagnosed with high-resolution imaging, which decreased the incidence of and delayed the time for the development of distant recurrences. Additional brain metastases can be diagnosed in 40% of patients by using high-resolution imaging. Thus, radiosurgical treatments based on high-resolution stereotactic MR imaging decrease the incidence of and lengthen the time to distant recurrences.

Computed tomography-guided gamma knife stereotactic radiosurgery for trigeminal neuralgia

Gamma knife stereotactic radiosurgery (GKSR) is an effective minimally invasive option for the treatment of medically refractory trigeminal neuralgia (TN). Optimal targeting of the retrogasserian trigeminal nerve target requires thin-slice, high-definition stereotactic magnetic resonance imaging (MRI). The purpose of this study was to evaluate management outcomes in TN patients ineligible for MRI and who instead underwent GKSR using computed tomography (CT). The authors reviewed their experience with CT-guided GKSR in 21 patients (median age: 75 years) with idiopathic TN. Contraindications to MRI included implanted pacemakers (n = 16), aneurysm clips (n = 2), cochlea implants (n = 1), metallic vascular stents (n = 1) or severe obesity (weight of 163 kg, n = 1). Contrast-enhanced CT at 1- or 1.25-mm intervals was acquired in all patients. One patient also underwent CT cisternography. The median target dose for GKSR was 80 Gy. The median follow-up was 35 months after GKSR. Treatment outcomes were compared to 459 patients who underwent MRI-guided GKSR for TN at our institute in the same time interval. Targeting of the trigeminal nerve guided by CT scan was feasible in all patients. Stereotactic frame titanium pin-related artifacts that interfered with full visualization of the trigeminal nerve were found in one patient who had the ipsilateral posterior pin placed near the inion. After GKSR, 90% of patients achieved initial pain relief that was adequate or better, with or without medication (Barrow Neurological Institute pain scores I-IIIb). Median time to pain relief was 2.6 weeks. Pain relief was maintained in 81% at 1 year, 66% at 2 years, and 46% at 5 years. Eight (42%) of 19 patients who achieved initial pain relief reported some recurrent pain at a median of 18 months after GKSR. Some degree of facial sensory dysfunction occurred in 19% of patients within 24 months of GKSR. These results are comparable to those of patients who had MRI-guided GKSR. CT-guided GKSR provides a similar rate of pain relief as MRI-guided radiosurgery. The posterior pins should be placed at least 1 cm away from the inion to reduce pin and frame-related artifacts on the targeting CT scan. This study indicates that GKSR using CT targeting is appropriate for patients with medically refractory TN who are unsuitable for MRI.

Effect of fiducial marker defects on stereotactic target localization in the Leksell stereotactic system

The stereotactic procedure in neurosurgery is a minimally invasive technique used to treat intracranial lesions. The fiducial markers of a frame-based stereotactic procedure are important for defining the stereotactic coordinate system and in locating the target. These markers are often defective in stereotactic images owing to the presence of air bubbles in the imaging indicator. We have assessed the effect of these defects on the registration of an image and on the localization of a target. The virtual phantom method was employed to simulate various types of defect. The virtual images were registered using the Leksell GammaPlan® (LGP) radiosurgery planning system, and the image definition and the target localization errors were assessed. As a result, the effect of the defects was most severe when the majority of the marker disappeared, but not all, especially in the posterior region. The mean and maximum image definition errors were 0.1 and 1.4 mm, which caused the mean target localization error to be 0.2 and 0.0 mm in LGP version 5.34 and 8.3.1, respectively. It is recommended to exclude images with defective fiducial markers during the image definition procedure to minimize subsequent errors, though the newest version of LGP (version 8.3.1) corrects localization errors.

Editorial: Gamma Knife and meningiomas

Editorial: Gamma Knife and meningiomas

Improving Targeting in Image-Guided Frame-Based Deep Brain Stimulation

Deep brain stimulation (DBS) is commonly used in the treatment of movement disorders such as Parkinson disease (PD), dystonia, and other tremors. To examine systematic errors in image-guided DBS electrode placement and to explore a calibration strategy for stereotactic targeting. Pre- and postoperative stereotactic MR images were analyzed in 165 patients. The perpendicular error between planned target coordinates and electrode trajectory was calculated geometrically for all 312 DBS electrodes implanted. Improvement in motor unified PD rating scale III subscore was calculated for those patients with PD with at least 6 months of follow-up after bilateral subthalamic DBS. Mean (standard deviation) scalar error of all electrodes was 1.4(0.9) mm with a significant difference between left and right hemispheres. Targeting error was significantly higher for electrodes with coronal approach angle (ARC) ≥10° (P < .001). Mean vector error was X: -0.6, Y: -0.7, and Z: -0.4 mm (medial, posterior, and superior directions, respectively). Targeting error was significantly improved by using a systematic calibration strategy based on ARC and target hemisphere (mean: 0.6 mm, P < .001) for 47 electrodes implanted in 24 patients. Retrospective theoretical calibration for all 312 electrodes would have reduced the mean (standard deviation) scalar error from 1.4(0.9) mm to 0.9(0.5) mm (36% improvement). With calibration, 97% of all electrodes would be within 2 mm of the intended target as opposed to 81% before calibration. There was no significant correlation between the degree of error and clinical outcome from bilateral subthalamic nucleus DBS (R = 0.07). After calibration of a systematic targeting error an MR image-guided stereotactic approach would be expected to deliver 97% of all electrodes to within 2 mm of the intended target point with a single brain pass.

Analysis of radiosurgical results in patients with brain metastases according to the number of brain lesions: is stereotactic radiosurgery effective for multiple brain metastases?

Whole-brain radiation therapy (WBRT), open resection, and stereotactic radiosurgery (SRS) are widely used for treatment of metastatic brain lesions, and many physicians recommend WBRT for multiple brain metastases. However, WBRT can be performed only once per patient, with rare exceptions. Some patients may require SRS for multiple metastatic brain lesions, particularly those patients harboring more than 10 lesions. In this paper, treatment results of SRS for brain metastasis were analyzed, and an attempt was made to determine whether SRS is effective, even in cases involving multiple metastatic brain lesions. The authors evaluated the cases of 323 patients who underwent SRS between October 2005 and October 2008 for the treatment of metastatic brain lesions. Treatment was performed using the Gamma Knife model C or Perfexion. The patients were divided into 4 groups according to the number of lesions visible on MR images: Group 1, 1-5 lesions; Group 2, 6-10 lesions: Group 3, 11-15 lesions; and Group 4, > 15 lesions. Patient survival and progression-free survival times, taking into account both local and distant tumor recurrences, were analyzed. The patients consisted of 172 men and 151 women with a mean age at SRS of 59 years (range 30-89 years). The overall median survival time after SRS was 10 months (range 8.7-11.4 months). The median survival time of each group was as follows: Group 1, 10 months; Group 2, 10 months; Group 3, 13 months; and Group 4, 8 months. There was no statistical difference between survival times after SRS (log-rank test, p = 0.554), although the probability of development of new lesions in the brain was greater in Group 4 (p = 0.014). Local tumor control rates were not statistically different among the groups (log-rank test, p = 0.989); however, remote disease progression was more frequent in Group 4 (log-rank test, p = 0.014). In this study, patients harboring more than 15 metastatic brain lesions were found to have faster development of new lesions in the brain. This may be due to the biological properties of the patients' primary lesions, for example, having a greater tendency to disseminate hematogenously, especially to the brain, or a higher probability of missed or invisible lesions (microscopic metastases) to treat on stereotactic MR images at the time of radiosurgery. However, the mean survival times after SRS were not statistically different between groups. According to the aforementioned results, SRS may be a good treatment option for local control of metastatic lesions and for improved survival in patients with multiple metastatic brain lesions, even those patients who harbor more than 15 metastatic brain lesions, who, after SRS, may have early and easily detectable new metastatic lesions.

Image quality of digital direct flat-panel mammography versus an indirect small-field CCD technique using a high-contrast phantom.

Objective. To compare the detection of microcalcifications on mammograms of an anthropomorphic breast phantom acquired by a direct digital flat-panel detector mammography system (FPM) versus a stereotactic breast biopsy system utilizing CCD (charge-coupled device) technology with either a 1024 or 512 acquisition matrix (1024 CCD and 512 CCD). Materials and Methods. Randomly distributed silica beads (diameter 100–1400 μm) and anthropomorphic scatter bodies were applied to 48 transparent films. The test specimens were radiographed on a direct digital FPM and by the indirect 1024 CCD and 512 CCD techniques. Four radiologists rated the monitor-displayed images independently of each other in random order. Results. The rate of correct positive readings for the “number of detectable microcalcifications” for silica beads of 100–199 μm in diameter was 54.2%, 50.0% and 45.8% by FPM, 1024 CCD and 512 CCD, respectively. The inter-rater variability was most pronounced for silica beads of 100–199 μm in diameter. The greatest agreement with the gold standard was observed for beads >400 μm in diameter across all methods. Conclusion. Stereotactic spot images taken by 1024 matrix CCD technique are diagnostically equivalent to direct digital flat-panel mammograms for visualizing simulated microcalcifications >400 μm in diameter.

Recurrent astroblastoma treated with gamma knife radiosurgery

Astroblastomas are exceedingly rare central nervous system tumors. Surgical resection is the standard initial treatment for astroblastomas. Still, some astroblastomas that have been completely resected recur. The optimal treatment for these lesions is unclear. There are no previous reports of the use of Gamma Knife radiosurgery in the treatment of astroblastomas. The patient is a 58 year old woman who had undergone resection of a left parieto-occipital tumor at an outside hospital in 2002, with repeat resection for recurrences in 2005 and 2007. Pathologic analysis at the Mayo Clinic demonstrated the tumor to be a low-grade astroblastoma. Repeat imaging in 2008 again demonstrated recurrence, and the patient was referred to our center for Gamma Knife radiosurgery. Pre and post-contrast T1 stereotactic MR images were obtained and imported into the treatment planning system for the Gamma Knife Perfexion. Two foci of tumor consistent with the patient's known left parietal astroblastoma were identified. A prescription dose of 18.00 Gy to the 50% isodose was delivered, and 16 isocenters were used. Follow-up imaging 17 months post-radiosurgery demonstrated a decrease in tumor size. Gamma Knife radiosurgery represents a useful treatment modality for recurrent astroblastomas. While surgical resection of low grade astroblastomas can be curative, Gamma Knife radiosurgery may be beneficial in cases where gross total resection is not feasible.

Stereotactic radiation treatment of vestibular schwannoma: indications, limitations, and outcomes

Stereotactic radiation treatment is an increasingly performed procedure for patients with vestibular schwannoma and other benign skull base tumors. During the past 30 years, advancements in stereotactic imaging, radiation delivery techniques, and dose planning have improved overall patient outcomes. The specific role of radiation in current management strategies for vestibular schwannoma continues to evolve as long-term outcome data are analyzed and standardized studies are performed. The recent literature regarding the indications, limitations, and outcomes for stereotactic radiation treatment is reviewed. Systematic reviews of the Gamma Knife literature demonstrate improved overall outcomes with radiation doses below 13 Gy. Observation of small vestibular schwannomas is recommended over early radiation or microsurgical intervention. Radiation may be used as adjunctive therapy for large tumors and in certain postradiation treatment failures. Stereotactic radiosurgery and fractionated radiotherapy are equally effective treatment modalities. Long-term outcome data will ultimately define future indications and limitations for the use of stereotactic radiation with benign skull base lesions. Current evidence supports its use for small to medium sized primary and recurrent vestibular schwannomas with optimal dosing below 13 Gy. It is also recommended for adjunctive therapy, recurrent tumors, in poor surgical candidates, and for those who do not desire observation or surgery.

Minimizing Brain Shift in Stereotactic Functional Neurosurgery

Stereotactic functional neurosurgical interventions depend on precise anatomic targeting before lesioning or deep brain stimulation (DBS) electrode placement. To examine the degree of subcortical brain shift observed when adopting an image-guided approach to stereotactic functional neurosurgery. Coordinates for the anterior and posterior commissural points (AC and PC) were recorded on thin-slice stereotactic magnetic resonance imaging (MRI) scans performed before and immediately after DBS electrode implantation in 136 procedures. The changes in length of AC-PC and in stereotactic coordinates for AC and PC were calculated for each intervention. In patients with Parkinson disease undergoing bilateral subthalamic nucleus (STN) DBS with at least 6 months of follow-up, pre- and postoperative scores of the motor part of the Unified Parkinson's Disease Rating Scale (UPDRS-III) were reviewed. Mean (SD) change in AC-PC length (DeltaAC-PC) was 0.6 (0.4) mm. There was no statistically significant difference in DeltaAC-PC between groups when examining anatomic target subgroups (P =.95), age subgroups (P = .63), sex (P = .59), and unilateral versus bilateral implantation (P =.15). The mean (SD) vector changes for the commissural points were: -0.1 (0.3) mm in X, -0.4 (0.6) mm in Y, and -0.1 (0.7) mm in Z for the AC; and -0.1 (0.3) mm in X, -0.2 (0.7) mm in Y, and 0.0 (0.7) mm in Z for the PC. There was a negligible correlation between the magnitude of brain shift and percentage improvement in UPDRS-III off-medication in patients undergoing STN DBS for PD (R <0.01). Brain shift has long been considered an issue in stereotactic targeting during DBS procedures. However, with the image-guided approach and surgical technique used in this study, subcortical brain shift was extremely limited and did not appear to adversely affect clinical outcome.

Iso-C/3-Dimensional Neuronavigation versus Conventional Fluoroscopy for Minimally Invasive Pedicle Screw Placement in Lumbar Fusion

Minimally invasive spinal surgery (MISS) has evolved over the past years due to the combination of microsurgery, minimal access strategies and neuronavigation. Percutaneous or mini-open pedicle screw placement is a challenge, especially for surgeons not experienced in the use of biplanar fluoroscopy or stereotactic imaging techniques. The aim of the study was to compare the precision of pedicle screw fixation for lumbar fusion procedures using Iso-C/stereotactic 3D neuronavigation (3D NAV) vs. standard AP/lateral fluoroscopy (2D NAV). Our first 42 patients undergoing MISS for one- or 2-level lumbar or lumbosacral fusion procedures for degenerative lumbar pathology were included in this study. Either 3D NAV (n=29) or standard fluoroscopy (n=13) was used to aid screw placement. Demographics, operative time, blood loss, and screw placement accuracy were evaluated. Screw placement was evaluated postoperatively using lumbar CT scanning. Accuracy of 3D NAV was evaluated by comparing intraoperative planning screenshots to postoperative CT placement of screws. There were no significant differences between groups for mean age, gender or intraoperative blood loss. 90.9% of 3D NAV screws and 73.7% of fluoroscopy screws had no pedicle perforation (p=0.04). Intraoperative navigation screenshots accurately predicted pedicle screw placement in 90.9% of cases. There was a positive correlation between 3D NAV accuracy and better screw grade (rs 0.45, p=0.036). Utilization of 3D NAV for percutaneous or mini-open lumbar screw placement during the early learning curve for MISS was associated with higher screw accuracy. This study demonstrates that the use of 3D navigation can facilitate the learning curve for MISS.

MRI-guided STN DBS in Parkinson's disease without microelectrode recording: efficacy and safety

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a commonly employed therapeutic procedure for patients with Parkinson's disease uncontrolled by medical therapies. This series describes the outcomes of...

Evaluation of the setup accuracy of a stereotactic radiotherapy head immobilization mask system using kV on‐board imaging

The purpose of this study was to evaluate setup accuracy and quantify random and systematic errors of the BrainLAB stereotactic immobilization mask and localization system using kV on‐board imaging. Nine patients were simulated and set up with the BrainLAB stereotactic head immobilization mask and localizer to be treated for brain lesions using single and hypofractions. Orthogonal pairs of projections were acquired using a kV on‐board imager mounted on a Varian Trilogy machine. The kV projections were then registered with digitally‐reconstructed radiographs (DRR) obtained from treatment planning. Shifts between the kV images and reference DRRs were calculated in the different directions: anterior‐posterior (A‐P), medial‐lateral (R‐L) and superior‐inferior (S‐I). If the shifts were larger than 2 mm in any direction, the patient was reset within the immobilization mask until satisfying setup accuracy based on image guidance has been achieved. Shifts as large as 4.5 mm, 5.0 mm, 8.0 mm in the A‐P, R‐L and S‐I directions, respectively, were measured from image registration of kV projections and DRRs. These shifts represent offsets between the treatment and simulation setup using immobilization mask. The mean offsets of 0.1 mm, 0.7 mm, and −1.6 mm represent systematic errors of the BrainLAB localizer in the A‐P, R‐L and S‐I directions, respectively. The mean of the radial shifts is about 1.7 mm. The standard deviations of the shifts were 2.2 mm, 2.0 mm, and 2.6 mm in A‐P, R‐L and S‐I directions, respectively, which represent random patient setup errors with the BrainLAB mask. The BrainLAB mask provides a noninvasive, practical and flexible immobilization system that keeps the patients in place during treatment. Relying on this system for patient setup might be associated with significant setup errors. Image guidance with the kV on‐board imager provides an independent verification technique to ensure accuracy of patient setup. Since the patient may relax or move during treatment, uncontrolled and undetected setup errors may be produced with patients that are not well‐immobilized. Therefore, the combination of stereotactic immobilization and image guidance achieves more controlled and accurate patient setup within 2 mm in A‐P, R‐L and S‐I directions.PACS numbers: 87.56.‐v, 87.56.Da

Subthalamic and red nucleus volumes in patients with Parkinson’s disease: Do they change with disease progression?

Objective To examine a possible correlation between disease progression and the volumes of the subthalamic nucleus (STN) and red nucleus (RN) in patients with Parkinson disease (PD). Methods Twelve patients with PD (mean time since diagnosis 10.8 ± 2.9 years) and age-matched 12 normal control subjects were enrolled. The volumes of the STN and RN were measured using 3-dimensional volume reconstructions of stereotactic magnetic resonance images. Results The PD and control groups were similar with regard to age and gender. The STN volume was 0.13 ± 0.01 cm 3 (mean ± SD) in PD patients and 0.27 ± 0.01 cm 3 in controls ( P < .001). The RN volume was 0.31 ± 0.02 cm 3 in PD patients and 0.21 ± 0.02 cm 3 in controls ( P = .002). Positive correlations of RN volume with time since diagnosis ( P = .004) and disease stage ( P = .01) were observed. On average, the STN volumes were 48% smaller and RN volumes 32% larger in PD patients than in control subjects; the volumes of the two nuclei were negatively correlated ( r = −0.46; P = .03). Conclusions Our results suggest that advanced disease stage and longer disease duration are associated with increased RN volume. STN volume was significantly smaller in Parkinson group. These findings may be useful in estimating disease status and rate of progression, and may also have implications for surgical treatment. Larger studies are needed to validate these results and determine their usefulness.

11C-methionine uptake correlates with tumor cell density rather than with microvessel density in glioma: A stereotactic image-histology comparison

11C-methionine positron emission tomography (11C-methionine PET) provides accurate detection of brain tumors. Several reports have analyzed the correlation between uptake of 11C-methionine and Ki-67 index or microvessel density non-stereotactically and suggested that 11C-methionine uptake reflects both proliferation potential and angiogenic capability in gliomas. As gliomas possess heterogeneous histological architecture, non-stereotactic comparison of the histology and 11C-methionine PET image may not be accurate. In the present study, the correlation between 11C-methionine uptake and cell or microvessel density was analyzed using histological specimens obtained by stereotactic biopsy, and an exact local comparison of 11C-methionine PET image and histological specimens was conducted. The tumor/normal tissue (T/N) ratio of 11C-methionine positron emission tomography was found to correlate better with cell density (R=0.747, p=0.000042) and Ki-67 index (R=0.675, p=0.00041) than with microvessel density (R=0.467, p=0.025) in a histological comparison using a stereotactic image. Furthermore, multiple linear regression analysis revealed that cell density was the key determinant for predicting 11C-methionine level while microvessel density was not. These results suggest that cell density contributes more to 11C-methionine uptake than microvessel density in glioma tissues and that the previously reported correlation of 11C-methionine uptake and microvessel density in glioma patients requires reevaluation.

Assessment of Radiosurgical Treatment by 11C-Methionine PET after Stereotactic Radiosurgery with Helical Tomotherapy to Metastatic Brain Tumors

Assessment of Radiosurgical Treatment by 11C-Methionine PET after Stereotactic Radiosurgery with Helical Tomotherapy to Metastatic Brain Tumors

Failure rate of contemporary low-dose radiosurgical technique for vestibular schwannoma Clinical article

Object The decline in cranial nerve morbidity after radiosurgery for vestibular schwannoma (VS) correlates with dose reduction and other technical changes to this procedure. The effect these changes have had on tumor control has not been well documented. Methods The authors performed a retrospective review of 293 patients with VSs who underwent radiosurgery between 1990 and 2004 and had a minimum of 24 months of imaging follow-up (90% of the entire series). The median radiation dose to the tumor margin was 13 Gy. Treatment failure was defined as progressive tumor enlargement noted on 2 or more imaging studies. The mean postradiosurgical follow-up was 60.9 ± 32.5 months. Results Tumor growth was noted in 15 patients (5%) at a median of 32 months after radiosurgery. Radiographically demonstrated tumor control was 96% at 3 years and 94% at 7 years after radiosurgery. Univariate analysis revealed 2 factors that correlated with failed radiosurgery for VS: an increasing number of isocenters (p = 0.03) and tumor margin radiation doses ≤ 13 Gy (p = 0.02). Multivariate analysis showed that only an increasing number of isocenters correlated with failed VS radiosurgery (hazard ratio 1.1, 95% CI 1.02–1.32, p &lt; 0.05). The tumor margin radiation dose (p = 0.22) was not associated with tumor growth after radiosurgery. Conclusions Distortion of stereotactic MR imaging coupled with increased radiosurgical conformality and progressive dose reduction likely caused some VSs to receive less than the prescribed radiation dose to the entire tumor volume.