David Hung-Chi Pan

Gamma knife surgery for vestibular schwannoma: 10-year experience of 195 cases

OBJECT The authors conducted a study to determine the optimal radiation dose for vestibular schwannoma (VS) and to examine the histopathology in cases of treatment failure for better understanding of the effects of irradiation. METHODS A retrospective study was performed of 195 patients with VS; there were 113 female and 82 male patients whose mean age was 51 years (range 11-82 years). Seventy-two patients (37%) had undergone partial or total excision of their tumor prior to gamma knife surgery (GKS). The mean tumor volume was 4.1 cm3 (range 0.04-23.1 cm3). Multiisocenter dose planning placed a prescription dose of 11 to 18.2 Gy on the 50 to 94% isodose located at the tumor margin. Clinical and magnetic resonance (MR) imaging follow-up evaluations were performed every 6 months. A loss of central enhancement was demonstrated on MR imaging in 69.5% of the patients. At the latest MR imaging assessment decreased or stable tumor volume was demonstrated in 93.6% of the patients. During a median follow-up period of 31 months resection was avoided in 96.8% of cases. Uncontrolled tumor swelling was noted in five patients at 3.5, 17, 24, 33, and 62 months after GKS, respectively. Twelve of 20 patients retained serviceable hearing. Two patients experienced a temporary facial palsy. Two patients developed a new trigeminal neuralgia. There was no treatment-related death. Histopathological examination of specimens in three cases (one at 62 months after GKS) revealed a long-lasting radiation effect on vessels inside the tumor. CONCLUSIONS Radiosurgery had a long-term radiation effect on VSs for up to 5 years. A margin 12-Gy dose with homogeneous distribution is effective in preventing tumor progression, while posing no serious threat to normal cranial nerve function.

Gamma knife radiosurgery for craniopharyngiomas.

The purpose of this paper was to note a potential source of error in magnetic resonance (MR) imaging. Magnetic resonance images were acquired for stereotactic planning for GKS of a vestibular schwannoma in a female patient. The images were acquired using three-dimensional sequence, which has been shown to produce minimal distortion effects. The images were transferred to the planning workstation, but the coronal images were rejected. By examination of the raw data and reconstruction of sagittal images through the localizer side plate, it was clearly seen that the image of the square localizer system was grossly distorted. The patient was returned to the MR imager for further studies and a metal clasp on her brassiere was identified as the cause of the distortion.A-60-year-old man with medically intractable left-sided maxillary division trigeminal neuralgia had severe cardiac disease, was dependent on an internal defibrillator and could not undergo magnetic resonance imaging. The patient was successfully treated using computerized tomography (CT) cisternography and gamma knife radiosurgery. The patient was pain free 2 months after GKS. Contrast cisternography with CT scanning is an excellent alternative imaging modality for the treatment of patients with intractable trigeminal neuralgia who are unable to undergo MR imaging.The authors describe acute deterioration in facial and acoustic neuropathies following radiosurgery for acoustic neuromas. In May 1995, a 26-year-old man, who had no evidence of neurofibromatosis Type 2, was treated with gamma knife radiosurgery (GKS; maximum dose 20 Gy and margin dose 14 Gy) for a right-sided intracanalicular acoustic tumor. Two days after the treatment, he developed headache, vomiting, right-sided facial weakness, tinnitus, and right hearing loss. There was a deterioration of facial nerve function and hearing function from pretreatment values. The facial function worsened from House-Brackmann Grade 1 to 3. Hearing deteriorated from Grade 1 to 5. Magnetic resonance (MR) images, obtained at the same time revealed an obvious decrease in contrast enhancement of the tumor without any change in tumor size or peritumoral edema. Facial nerve function improved gradually and increased to House-Brackmann Grade 2 by 8 months post-GKS. The tumor has been unchanged in size for 5 years, and facial nerve function has also been maintained at Grade 2 with unchanged deafness. This is the first detailed report of immediate facial neuropathy after GKS for acoustic neuroma and MR imaging revealing early possibly toxic changes. Potential explanations for this phenomenon are presented.In clinical follow-up studies after radiosurgery, imaging modalities such as computerized tomography (CT) and magnetic resonance (MR) imaging are used. Accurate determination of the residual lesion volume is necessary for realistic assessment of the effects of treatment. Usually, the diameters rather than the volume of the lesion are measured. To determine the lesion volume without using stereotactically defined images, the software program VOLUMESERIES has been developed. VOLUMESERIES is a personal computer-based image analysis tool. Acquired DICOM CT scans and MR image series can be visualized. The region of interest is contoured with the help of the mouse, and then the system calculates the volume of the contoured region and the total volume is given in cubic centimeters. The defined volume is also displayed in reconstructed sagittal and coronal slices. In addition, distance measurements can be performed to measure tumor extent. The accuracy of VOLUMESERIES was checked against stereotactically defined images in the Leksell GammaPlan treatment planning program. A discrepancy in target volumes of approximately 8% was observed between the two methods. This discrepancy is of lesser interest because the method is used to determine the course of the target volume over time, rather than the absolute volume. Moreover, it could be shown that the method was more sensitive than the tumor diameter measurements currently in use. VOLUMESERIES appears to be a valuable tool for assessing residual lesion volume on follow-up images after gamma knife radiosurgery while avoiding the need for stereotactic definition.This study was conducted to evaluate the geometric distortion of angiographic images created from a commonly used digital x-ray imaging system and the performance of a commercially available distortion-correction computer program. A 12 x 12 x 12-cm wood phantom was constructed. Lead shots, 2 mm in diameter, were attached to the surfaces of the phantom. The phantom was then placed inside the angiographic localizer. Cut films (frontal and lateral analog films) of the phantom were obtained. The films were analyzed using GammaPlan target series 4.12. The same procedure was repeated with a digital x-ray imaging system equipped with a computer program to correct the geometric distortion. The distortion of the two sets of digital images was evaluated using the coordinates of the lead shots from the cut films as references. The coordinates of all lead shots obtained from digital images and corrected by the computer program coincided within 0.5 mm of those obtained from cut films. The average difference is 0.28 mm with a standard deviation of 0.01 mm. On the other hand, the coordinates obtained from digital images with and without correction can differ by as much as 3.4 mm. The average difference is 1.53 mm, with a standard deviation of 0.67 mm. The investigated computer program can reduce the geometric distortion of digital images from a commonly used x-ray imaging system to less than 0.5 mm. Therefore, they are suitable for the localization of arteriovenous malformations and other vascular targets in gamma knife radiosurgery.

Gamma knife surgery for cavernous hemangiomas: an analysis of 125 patients

OBJECT The authors sought to determine the value of gamma knife surgery (GKS) in the treatment of cavernous hemangiomas (CHs). METHODS Between 1993 and 2002, a total of 125 patients with symptomatic CHs were treated with GKS. Ninety-seven patients presented with bleeding and 45 of these had at least two bleeding episodes. Thirteen patients presented with seizures combined with hemorrhage, and 15 patients presented with seizures alone. The mean margin dose of radiation was 12.1 Gy and the mean follow-up time was 5.4 years. In the 112 patients who had bled the number of rebleeds after GKS was 32. These rebleeds were defined both clinically and based on magnetic resonance imaging for an annual rebleeding rate of 32 episodes/492 patient-years or 6.5%. Twenty-three of the 32 rebleeding episodes occurred within 2 years after GKS. Nine episodes occurred after 2 years; thus, the annual rebleeding rate after GKS was 10.3% for the first 2 years and 3.3% thereafter (p = 0.0038). In the 45 patients with at least two bleeding episodes before GKS, the rebleeding rate dropped from 29.2% (55 episodes/188 patient-years) before treatment to 5% (10 episodes/197 patient-years) after treatment (p < 0.0001). Among the 28 patients who presented with seizures, 15 (53%) had good outcomes (Engel Grades I and II). In this study of 125 patients, symptomatic radiation-induced complications developed in only three patients. CONCLUSIONS Gamma knife surgery can effectively reduce the rebleeding rate after the first symptomatic hemorrhage in patients with CH. In addition, GKS may be useful in reducing the severity of seizures in patients with CH.

Gamma Knife surgery for cerebral arteriovenous malformations in children: a 13-year experience

OBJECT Studies on the efficacy of arteriovenous malformation (AVM) radiosurgery have largely been conducted in the adult population. Clinically, the results may not always be applicable to pediatric patients. Moreover, studies involving the pediatric population have largely comprised small- (< 3 cm3) and medium-sized (3-10 cm3) AVMs. For large (> 10 cm3) AVMs in children, sparse radiosurgical results are available. The current study was conducted to further clarify the role of radiosurgery in the treatment of pediatric AVMs. METHODS A retrospective analysis was performed of data obtained in 105 pediatric patients (< 18 years of age) with cerebral AVMs treated by Gamma Knife surgery (GKS) between 1993 and 2006. For statistical comparison the authors studied data acquired in 458 adult patients with AVMs treated during the same period. The patients underwent follow-up magnetic resonance imaging at 6-month intervals. Cerebral angiography was used to confirm the obliteration of the AVM. RESULTS In pediatric patients, the AVM obliteration rate at 48 months after a primary GKS was 65%. Repeated GKS in those in whom primary treatments failed further ablated some AVMs, for an overall obliteration rate of 81%. The efficacy of GKS correlated with the size of the AVM: 91% for small, 86% for medium, and 64% for large AVMs. The treatments were associated with an 8% morbidity rate and < 1% mortality rate. Posttreatment hemorrhage occurred in 4 (4%) of 105 patients. Obliteration rates at 48 months of small and extremely large (> 20 cm3) AVMs were similar in the pediatric and adult groups, whereas AVMs between 3 and 10 cm3 responded less efficaciously in children (p = 0.042). The AVMs with volumes ranging from 10 to 20 cm3 were also associated with a lower obliteration rate in children at 48 months, but statistical significance was not reached (p = 0.279). CONCLUSIONS Gamma Knife surgery is an effective and safe treatment alternative for pediatric AVMs. The medium (3-10-cm3) and large (10-20-cm3) AVMs tend to respond less efficaciously than those of comparable size in adults.

Management of supratentorial cavernous malformations: craniotomy versus gammaknife radiosurgery

OBJECTIVE Although craniotomy is the preferred treatment for symptomatic solitary supratentorial cavernous malformation (CM), radiosurgery is also an option. Our aim was to see which of these strategies was the most effective and under what circumstances. METHODS Of the 46 patients with solitary supratentorial CM that we retrospectively studied, 24 presented with seizures, 16 with focal neurological deficits due to intracerebral hemorrhage, and 6 with both seizures and bleeding. Sixteen were treated with craniotomy and 30 with gammaknife radiosurgery (GKRS). The main outcome measures for comparing craniotomy with GKRS were the proportion of postoperative seizure-free patients and the proportion of patients in whom no rebleeding occurred. RESULTS Of patients presenting with seizures with/without bleeding, a significantly higher proportion of the craniotomy group than the GKRS group became and remained seizure-free (11/14 [79%] versus 4/16 [25%]; P < 0.002), and of those presenting with bleeding with/without seizures, a somewhat (though nonsignificantly) higher proportion did not rebleed (4/4 [100%] versus 12/18 [67%]) after surgery. The remaining 2 of the 16 craniotomy patients did not rebleed and had no residual tumor at follow up. Twelve of the 30 GKRS patients had evidence of tumor regression at follow up. CONCLUSION In the clinical management of solitary supratentorial CM, craniotomy for lesionectomy resulted in better seizure control and rebleeding avoidance than GKRS.

Gamma knife surgery for cavernous hemangiomas in the cavernous sinus.

BACKGROUNDCavernous hemangioma in the cavernous sinus (CS) is a rare vascular tumor. Direct microsurgical approach usually results in massive hemorrhage. Radiosurgery has emerged as a treatment alternative to microsurgery. OBJECTIVETo further investigate the role of Gamma Knife surgery (GKS) in treating CS hemangiomas. METHODSThis was a retrospective analysis of 7 patients with CS hemangiomas treated by GKS between 1993 and 2008. Data from 84 CS meningiomas treated during the same period were also analyzed for comparison. The patients underwent follow-up magnetic resonance imaging at 6-month intervals. Data on clinical and imaging changes after radiosurgery were analyzed. RESULTSSix months after GKS, magnetic resonance imaging revealed an average of 72% tumor volume reduction (range, 56%–83%). After 1 year, tumor volume decreased 80% (range, 69%–90%) compared with the pre-GKS volume. Three patients had > 5 years of follow-up, which showed the tumor volume further decreased by 90% of the original size. The average tumor volume reduction was 82%. In contrast, tumor volume reduction of the 84 cavernous sinus meningiomas after GKS was only 29% (P < .001 by Mann-Whitney U test). Before treatment, 6 patients had various degrees of ophthalmoplegia. After GKS, 5 improved markedly within 6 months. Two patients who suffered from poor vision improved after radiosurgery. CONCLUSIONGKS is an effective and safe treatment modality for CS hemangiomas with long-term treatment effect. Considering the high risks involved in microsurgery, GKS may serve as the primary treatment choice for CS hemangiomas.

Stereotactic radiosurgery for intracranial dural arteriovenous fistulas: a systematic review.

OBJECT The goal of this study was to evaluate the obliteration rate of intracranial dural arteriovenous fistulas (DAVFs) in patients treated with stereotactic radiosurgery (SRS), and to compare obliteration rates between cavernous sinus (CS) and noncavernous sinus (NCS) DAVFs, and between DAVFs with and without cortical venous drainage (CVD). METHODS A systematic literature review was performed using PubMed. The CS DAVFs and the NCS DAVFs were categorized using the Barrow and Borden classification systems, respectively. The DAVFs were also categorized by location and by the presence of CVD. Statistical analyses of pooled data were conducted to assess complete obliteration rates in CS and NCS DAVFs, and in DAVFs with and without CVD. RESULTS Nineteen studies were included, comprising 729 patients harboring 743 DAVFs treated with SRS. The mean obliteration rate was 63% (95% CI 52.4%-73.6%). Complete obliteration for CS and NCS DAVFs was achieved in 73% and 58% of patients, respectively. No significant difference in obliteration rates between CS and NCS DAVFs was found (OR 1.72, 95% CI 0.66-4.46; p=0.27). Complete obliteration in DAVFs with and without CVD was observed in 56% and 75% of patients, respectively. A significantly higher obliteration rate was observed in DAVFs without CVD compared with DAVFs with CVD (OR 2.37, 95% CI 1.07-5.28; p=0.03). CONCLUSIONS Treatment with SRS offers favorable rates of DAVF obliteration with low complication rates. Patients harboring DAVFs that are refractory or not amenable to endovascular or surgical therapy may be safely and effectively treated using SRS.

The Effectiveness and Factors Related to Treatment Results of Gamma Knife Radiosurgery for Meningiomas

A retrospective analysis was conducted on 80 patients with intracranial mengiomas treated with Gamma Knife radiosurgery between 1993 and 1996. The purpose was to analyze the efficacy of the treatment and to assess appropriate treatment parameters. The results were assessed by regular MR examinations, and tumor volume was measured at 6-month intervals. Mean follow-up duration was 21 months (range 6–45 months). 63 meningiomas were at the skull base and 17 were distal from the skull base. Tumor volumes <5 ml (n=38), 5–10 ml (n=21), 10–15 ml (n=14), 15–20 ml (n=7). The patients were divided into 3 groups according to the radiation dose. The groups were high-dose (peripheral dose 17–20 Gy, n=19), medium-dose (15–16 Gy, n=33) and low-dose (12–14 Gy, n=28) groups. A statistical method (Generalized Estimation Equation) was applied to compare treatment results in these groups with different doses and tumor volumes. The volume measurement at the latest follow-up showed 74% (59/80) meningiomas decreased in volume, 17% (14/80) had no tumor enlargement and 9% (7/80) had increased in volume. The increased volume was found more frequently in the patients with a short (6–12 months) follow-up period. In this series, the tumors had 32% reduction in average tumor volume at 3 years after radiosurgery. At the range of 12–20 Gy peripheral dose (PD), radiosurgery was effective to reduce tumor volume 0.7% per month (p<0.05). However, higher doses had no significant difference on tumor volume reduction (p>0.05). On the other hand, high-dose (PD>17 Gy) treatment was associated with a higher risk of temporary tumor swelling and the development of adverse radiation effects (AREs). The AREs detected on MR images occurred in (25/80) 31% patients. Only 6/25 AREs were symptomatic and 2 had neurological sequelae. Peripheral doses, tumor volumes and their locations had significant impacts on the ARE (p<0.05). In conclusion, a peripheral dose of 15–16 Gy may be adequate for meningiomas with small volumes (<5 ml). In larger tumors (>10 ml) a lower PD is preferred (12–14 Gy). To avoid initial tumor swelling and ARE, high-dose irradiation (PD>17 Gy) is not recommended for meningiomas larger than 5 ml.

Staged radiosurgery for extra-large cerebral arteriovenous malformations : method, implementation, and results

OBJECT The effectiveness and safety of radiosurgery for small- to medium-sized cerebral arteriovenous malformations (AVMs) have been well established. However, the management for large cerebral AVMs remains a great challenge to neurosurgeons. In the past 5 years the authors performed preplanned staged radiosurgery to treat extra-large cerebral AVMs. METHODS An extra-large cerebral AVM is defined as one with nidus volume > 40 ml. The nidus volume of cerebral AVM is measured from the dose plan-that is, as being the volume contained within the best-fit prescription isodose. From January 2003 to December 2007, the authors treated 6 patients with extra-large AVMs by preplanned staged GKS. Staged radiosurgery is implemented by rigid transformation with translation and rotation of coordinates between 2 stages. The average radiation-targeted volume was 60 ml (range 47-72 ml). The presenting symptoms were seizure in 4 patients and a bleeding episode in 2. One patient had undergone a previous craniotomy and evacuation of hematoma. The mean interval between the 2 radiosurgical sessions was 6.9 months (range 4.5-9.1 months). The prescribed marginal dose given to the nidus volume in each stage ranged from 16 to 18.6 Gy. The expected marginal dose of total nidus was 17-19 Gy. Regular follow-up MR imaging was performed every 6 months. The mean follow-up period was 28 months (range 12-54 months). RESULTS Most of the patients exhibited clinical improvement: relief of headache and reduced frequency of seizure attack. All patients had significant regression of nidus observed on MR imaging follow-up. Two patients had angiogram-confirmed complete obliteration of the nidus 45 and 60 months after the second-stage radiosurgical session. One patient experienced minor bleeding 8 months after the second-stage radiosurgery with mild headache. She had satisfactory recovery without clinical neurological deficit after conservative treatment. CONCLUSIONS These preliminary results indicate that staged radiosurgery is a practical strategy to treat patients with extra-large cerebral AVMs. It takes longer to obliterate the AVMs. The observed high signal T2 changes after the radiosurgery appeared clinically insignificant in 6 patients followed up for an average of 28 months. Longer follow-up is necessary to confirm its long-term safety.

1-11C-Acetate Versus 18F-FDG PET in Detection of Meningioma and Monitoring the Effect of γ-Knife Radiosurgery

This study aimed to define the potential of 1-11C-acetate PET, compared with 18F-FDG, in detecting meningiomas and monitoring the effect of γ-knife radiosurgery. Methods: Twenty-two patients with the neuroradiologic diagnosis of meningioma were examined by 1-11C-acetate and 18F-FDG PET on the same day. There were 12 cases of histopathologically proven meningioma (8 grade I, 2 grade II, and 2 grade III), 1 of tuberculous granuloma, and 1 of degenerative tissue. 1-11C-acetate PET scans of fasting patients were obtained 10 min after intravenous administration of 740 MBq of 1-11C-acetate. 18F-FDG PET was performed at 2 h after 1-11C-acetate scanning. The PET images were evaluated by a qualitative method and semiquantitative analysis using standardized uptake value and tumor-to-cortex ratio. Results: The 18F-FDG PET study revealed a hypometabolic focus in 17 meningiomas (8 grade I, 1 grade II, and 8 unknown grade) and hypermetabolism in 1 grade II and 2 grade III meningiomas. High uptake of 1-11C-acetate was observed in all 20 meningiomas, in contrast to the low uptake in surrounding normal brain tissue, allowing a clearer demarcation of the tumor boundary than that provided by 18F-FDG. Dissociation of regional accumulation of 1-11C-acetate and 18F-FDG within the tumor was also noted on the coregistered images. The standardized uptake value for 1-11C-acetate was not different from that for 18F-FDG (mean ± SD, 3.16 ± 1.75 vs. 3.22 ± 1.50, P = 0.601), but the tumor-to-cortex ratio for 1-11C-acetate was higher than that for 18F-FDG (3.46 ± 1.38 vs. 0.93 ± 1.08, P < 0.005). 18F-FDG was able to differentiate grade I from grade II–III meningiomas, whereas 1-11C-acetate was unable to do so. Tuberculous granuloma had a high 1-11C-acetate and 18F-FDG uptake similar to that of grade II/III meningioma. Five patients received 1-11C-acetate and 18F-FDG PET before and after γ-knife surgery. 1-11C-acetate performed better than did 18F-FDG in monitoring the response of tumor metabolism to radiosurgery. Conclusion: 1-11C-acetate was found to be useful for detecting meningiomas and evaluating the extent of meningiomas and potentially useful for monitoring tumor response to radiosurgery. However, 1-11C-acetate was not useful for evaluating the tumor grade. 18F-FDG was found to be less useful than 1-11C-acetate for evaluating the extent of meningiomas and the response to radiosurgical treatment but may be useful for differentiating benign from malignant meningiomas. 18F-FDG and 1-11C-acetate are complementary for assessing diverse cell metabolism of meningioma.