Wen-Yuh Chung

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.

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.

Protection of visual pathway in gamma knife radiosurgery for craniopharyngiomas.

Craniopharyngiomas present a major challenge to Gamma Knife radiosurgery (GKRS) due to their proximity to the optic apparatus. Based on observations of the evolving tumoral change on MRI and clinical results, an optimization of the treatment strategy and dose selection is possible. From March 1993 to September 1996, 21 patients with craniopharyngiomas were treated by GKRS. Every patient received stereotactic MRI exclusively for targeting and dose planning. The tumor and adjacent structures, including optic nerves, chiasm, and tracts were carefully identified and delineated on sagittal, coronal and axial films. The tumor volume ranged from 0.3 to 28 ml (average 9 ml). We purposefully apply multiple isocenters (average 9.1 shots) to create an isodose curve that covered the tumor optimally while sparing the optic pathway. The marginal dose prescribed was 9.5 to 16 Gy (50%). The maximal dose was 19 to 32 Gy. The maximal dose to the optic apparatus was 3.2 to 12.5 Gy. After GKRS, all patients were followed up clinically every month. MR studies were conducted every six months with the same techniques on the same scanner to investigate evolution of tumor volume and any adverse radiation effect. The follow-up period ranged from 6 to 40 months (mean: 18.4, median: 19). All patients were followed more than 6 months. Nineteen out of 21 cases (90.5%) achieved tumor control; that is, 18 tumor shrinkage (volume reduction: 15–95%) and 1 stabilized tumor growth. Among these 21 patients, 7 had improved visual acuity or visual field after GKRS, and the rest remained stable. Two patients developed mild T2 change on MRI without any endocrinological disturbance or visual impairment. Protection of the visual pathway can be secured by a sophisticated delineation on 3-dimensional stereotactic images with multiple-shot dose planning. Craniopharyngiomas with tumor volume up to 25 ml were treated safely and effectively, because the dose to the optic apparatus was kept as low as possiby this strategy. Further follow-up is needed to determine the highest tolerable dose to surrounding critical structures and the long-term outcome of tumor control.

Gamma knife radiosurgery for glomus jugulare and tympanicum.

Objective: To establish the role of gamma knife radiosurgery (GKS) as a treatment strategy for glomus jugulare and tympanicum. Method: A retrospective review of 14 glomus tumors, including 11 glomus jugulare and 3 glomus tympanicum tumors, which were treated by GKS in Taipei Veterans General Hospital from 1993 to 2009, was conducted. Two of these cases had undergone prior surgery with partial tumor resection, and the other 12 cases received primary treatment with GKS after a thorough neuroimaging and cerebral angiography. The tumor volume ranged from 6.5 to 22.1 ml. The maximum dose at the tumor center ranged from 21.6 to 26.3 Gy. All 14 patients were regularly followed up by clinical and radiological evaluations. The median follow-up time was 40.3 months. Results: All 14 patients had significant tumor regression after radiosurgery. The median tumor volume reduction was 34.0% (range 3–79%). Only 1 patient had temporary tumor volume progression (24% increment 6 months post-treatment), accompanied with unilateral facial palsy (from grade III to grade IV) and hearing impairment (from grade I to grade II). The tumor volume of this patient had regressed by 12 months, but facial palsy persisted. The tumor control rate in the series was 100% (n = 14/14), and the preservation rate of cranial nerve function was 92.8% (13/14). There was no complication of lower cranial nerve damage after radiosurgery. Conclusion: GKS appeared to be a good alternative or adjuvant to microsurgical resection in patients who are not amenable to complete surgical eradication, with an excellent tumor control rate and little morbidity after long-term follow-up.

An Evaluation of the Accuracy of Magnetic-Resonance-Guided Gamma Knife Surgery

An evaluation of the systematic accuracy of magnetic resonance (MR)-guided Gamma Knife surgery was performed. In two experiments, a cylinder phantom filled with dosimeter gel containing ferrous sulfate was fixed to a stereotactic frame. The gel phantom was irradiated with the Gamma Knife with a single shot using 4-mm collimators. The target point was set at the frame center of the stereotactic system giving coordinate values of X = 100, Y = 100, Z = 100. The maximum target dose was 15 Gy. MR imaging was undertaken immediately after the irradiation, using a superconductive 1.5-T MR scanner. Spin echo T1-weighted images, with transaxial, coronal, and sagittal views, were obtained. On the images, points with the highest signals were defined as the target point which received the maximum dose. Within the dose range of the experiment, this definition is based on a linear relationship between the dose to the gel and the T1 relaxation shortening after irradiation. The distances between the frame center and the target point defined on the MR images in the experiments were 0.12 mm (0.2375 pixels) and 0.43 mm (0.8515 pixels), respectively. Both are within the mechanical accuracy of the Gamma Knife. The imaging study confirms the accuracy of the Gamma Knife surgery used in the institution.

Early Effects of Gamma Knife Surgery on Malignant and Benign Intracranial Tumors

To assess the early response of intracranial tumors to Gamma Knife surgery, we performed a prospective investigation of 42 patients treated by Gamma Knife surgery for different types of intracranial tumors. The clinical condition, tumor volume, treatment results and their temporal correlation with the irradiation were analyzed, based on MRI performed on the same MR scanner. Volume reduction in the tumors measured at the latest follow-up ranged from 0.2 to 100%. All except 1 malignant tumor showed decreasing size and improving peritumoral edema 1-7 months after radiosurgery. In 30 benign tumors, 13 showed either a decrease or no change in volume. However, an initial volume increase was observed in 17 tumors, with a maximum at 3-9 months, which subsequently regressed. In 2 meningioma patients, peritumoral edema increased and needed steroid treatment. Sequential PET-FDG imaging of the patients showed decreasing FDG uptake, indicating a decrease tumor in metabolism. The PET findings correlated well with the loss of contrast enhancement on MR images. In conclusion, intracranial tumors respond to Gamma Knife surgery from an early stage. Different tumors have different responses to radiosurgery. It is too early to offer a prognosis of long-term effects based on the limited material. However, sequential clinical, MR and PET follow-ups provide an excellent opportunity to investigate the evolving irradiation effects in vivo.

Early irradiation effects observed on magnetic resonance imaging and angiography, and positron emission tomography for arteriovenous malformations treated by Gamma Knife radiosurgery

In 14 patients (7 males and 7 females, age 16-49, mean 29 years), medium-to-large arteriovenous malformations (AVMs; nidus volume 3.5-17.5 cm3, mean 9.4 cm3) were treated by Gamma Knife radiosurgery. Stereotactic MR and conventional angiography were included for targeting to improve targeting accuracy and tissue content in the irradiation volume. Maximum irradiation doses to the nidi were 36-40 Gy (mean 38.9 Gy) and minimum target doses were 18-24 Gy (mean 20 Gy). MR images and MR angiography demonstrated decreasing caliber of feeding vessels and AVM nidus volumes from an early stage, 3 months after radiosurgery, which indicated improvement in cerebral hemodynamics. The improvement correlated well with that observed on PET using [18F]fluorodeoxyglucose (FDG) and with the patients clinical condition. MR creates an opportunity to monitor treatment effects in a completely noninvasive manner, while conventional angiography remains necessary for verifying complete obliteration of AVMs. More patients and longer follow-ups are needed for clarifying the role of MR techniques in radiosurgery for AVMs.

Delayed microsurgery for vestibular schwannoma after gamma knife radiosurgery.

Stereotactic radiosurgery for vestibular schwannomas (VSs) has become popular during the last decade with promising clinical results after long-term follow-up. However, on rare occasions, some cases have needed traditional microsurgery to remove the tumor several months or years after radiosurgery. We present a retrospective analysis of data acquired during a 16-year period in delayed microsurgery of seven patients with VSs who underwent gamma knife surgery (GKS). A total of 444 with VS underwent GKS between March 1993 and December 2008, and 7 (1.57%) underwent delayed microsurgery at a median of 26xa0months (range from 3xa0months to 6xa0years) after GKS. The mean size of the tumor during GKS was 10.4xa0ml (range 2.3–23.5xa0ml). These seven patients were younger, and female predominant. The indications of microsurgery included adverse radiation effect with peri-focal edema, tumor enlargement, and cyst enlargement. Although the perifocal edema could lead to more difficulty in surgery than in typically performed operations for schwannoma, subtotal resection was achieved in all patients. There was no surgery-related morbidity or mortality. The histology showed benign tumor in five patients, malignant peripheral nerve sheath tumor in one, and necrotic tissue in one. The need of microsurgery for further treatment of VS after radiosurgery is rare, but can be a challenge to neurosurgeons in terms of surgical indication, timing, and techniques. The authors concluded the incidence of delayed microsurgery was 1.57% in a series of 444 patients over a 16-year period. We concluded some experience from operative indications, timing, approach, and outcome.

The radiation induced magnetic resonance image intensity change provides a more efficient three‐dimensional dose measurement in MRI–Fricke–agarose gel dosimetry

A detailed methodology has been developed to map the spatial dose distribution in a Fricke-agarose gel based on the radiation induced image intensity change in the gels magnetic resonance (MR) images. Besides the linear correlation between the change in the gels spin-lattice relaxation rate and the absorbed dose, it is shown here that the radiation induced image intensity change for T1-weighted spin-echo images with TE << TR correlates exponentially to the absorbed dose. Furthermore, at the lower dose region (< 15 Gy), the correlation is fairly linear and its sensitivity is high. The minimum detectable dose is shown to be equivalent to the one obtained using the conventional R1-based approach. Since only one T1-weighted image is required for the dose evaluation, compared to the R1-based method, the total MR imaging time can be reduced from hours to a few minutes. This extensive time reduction avoids ferric ion diffusion effects and provides a practical way to simply and effectively measure the three-dimensional dose distribution using the Fricke-agarose dosimeter gel.

Do We Need Conventional Angiography

Sixteen cerebral arteriovenous malformations (AVMs) were examined to determine the role of magnetic resonance (MR) imaging in verifying obliteration. The AVMs (mean volume 7.5 cm3, range 2–