Chuan-Fu Huang

Gamma Knife surgery for trigeminal pain caused by benign brain tumors

OBJECT The authors report the effects of Gamma Knife surgery (GKS) on benign tumor-related trigeminal pain in patients who underwent follow-up for a mean 57.8 months. METHODS From 1999 to 2004, 21 patients with benign tumor-related trigeminal pain (12 meningiomas and 9 schwannomas) underwent GKS as a primary or repeated treatment. These patients harbored tumors within the radiosurgical target area. For meningiomas, the mean radiosurgical treatment volume was 8.2 ml (range 1.1-21 ml), and the mean radiosurgical tumor margin dose was 12.7 Gy (range 12-15 Gy); for schwannomas, the mean volume was 5.6 ml (range 2-9.2 ml), and the mean marginal dose was 13 Gy (range 11.5-16 Gy). Seven patients underwent retreatment for recurrent or persistent pain; the ipsilateral trigeminal nerve or ganglion was identified and a mean maximal dose of 60.7 Gy (range 40-70 Gy) was delivered to these targets. In 1 patient undergoing retreatment, the margin dose was 12 Gy. The mean age at the time of radiosurgery was 54.5 years (range 18-79 years). RESULTS The mean follow-up period was 57.8 months (range 36-94 months). Overall, 12 (57%) of 21 patients experienced pain relief without medication after the first GKS and the mean time to drug discontinuation was 10.5 months (range 2-24 months). Initial pain improvement was noted in 17 patients (81%) with a mean time of 3.7 months (range 1 week-10 months) after GKS. Eight patients underwent repeated GKS for persistent and recurrent pain. Four patients (50%) had complete pain relief. The final results of the first and repeated GKS were excellent in 16 patients (76%), and in only 1 patient did GKS fail, and this patient later underwent open surgery. For all 21 patients (100%), control of tumor growth was documented at a mean of 46 months after GKS. Three of 6 patients with pre-GKS facial numbness reported improvement, but 4 suffered new facial numbness after repeated GKS. CONCLUSIONS Gamma Knife surgery appears to be an effective tool to treat benign tumor-related trigeminal pain and control tumor growth. Repeated GKS targeting the trigeminal root or ganglion can be considered a tool to enhance the efficacy of pain management if pain persists or recurs, but the optimum treatment dose needs further investigation.

Gamma Knife surgery used as primary and repeated treatment for idiopathic trigeminal neuralgia

OBJECT The purpose of this study was to assess the outcome of idiopathic trigeminal neuralgia (TN) treated with Gamma Knife surgery (GKS) as a primary and repeated treatment modality with a mean follow-up of 5.7 years. METHODS Between July 1999 and September 2005, a total of 89 patients with idiopathic TN underwent GKS as a primary treatment. The entry zone of the TN was targeted with a 4-mm collimator and treated with a maximal dose of 60-90 Gy (mean 79 Gy). The dose to the pontine margin was always kept < 15 Gy. Twenty patients received repeated GKS for recurrent or residual pain with a maximal dose of 40-76 Gy (mean 52 Gy). For the second procedure, the target was positioned at the same location as the first treatment. RESULTS The mean follow-up period was 68 months (range 32-104 months). Sixty-nine (77.5%) of the 89 patients experienced a favorable response, as follows: 50 (56%) had excellent, 12 (13.5%) had good, and 7 (7.8%) had fair outcomes. The mean time to pain relief was 1.1 months (range 2 days-6 months). No significant correlation, but more likely a tendency, was found between the dose and pain relief (p = 0.08). Also, no correlation was noted for facial numbness (p = 0.77). The mean follow-up period after repeated GKS was 60 months (range 32-87 months). Outcomes after repeated GKS were excellent in 11 patients (55%) and good in 1 (5%). Seven patients experienced facial numbness. No correlation was found between the additive dose and pain relief (p = 0.24) or facial numbness (p = 0.15). Final outcomes of primary and repeated GKS were excellent in 61 (68.5%), good in 13 (14.6%), and fair in 7 (7.9%). In total, 91% of the patients were successfully treated with this method. There was no statistical significance for efficacy between primary and repeated GKS (p = 0.65), but there was a significant difference for facial numbness (p = 0.007). CONCLUSIONS Gamma Knife surgery established durable pain relief when used as a primary and repeated surgery. Treatment was successful for a total of 91% of patients at a mean follow-up of 5.7 years, but facial numbness was also relatively higher.

Gamma Knife surgery for recurrent or residual trigeminal neuralgia after a failed initial procedure

OBJECT The purpose of this study was to assess outcomes of Gamma Knife surgery (GKS) as a second treatment for recurrent or residual trigeminal neuralgia (TN) after failure of 3 initial procedures: microvascular decompression (MVD), GKS, and percutaneous radiofrequency rhizotomy (PRR). METHODS Between 1999 and 2008, 65 patients (31 men [48%] and 34 women [52%]) with recurrent TN were treated with GKS. All 65 patients had undergone previous medical procedures that failed to achieve sufficient pain relief: 27 patients (42%) had undergone MVD, 8 (12%) had undergone PRR, and 30 (46%) had undergone GKS as the initial treatment. The entry zone of the trigeminal nerve was targeted using a 4-mm collimator and treated with 35-90 Gy. The isocenter was positioned so that the brainstem surface was usually irradiated at an isodose no greater than 20% (59 patients) to 30% (6 patients). The median duration of TN symptoms in these patients was 39 months (range 1-192 months). RESULTS At the clinical evaluation, 42 patients (65%) with idiopathic TN reported successful pain control at a median follow-up point of 64 months (range 18-132 months). Of these patients, 33 (51%) were no longer using medication. At the 1-, 2-, and 3-year follow-up examinations, 74%, 71%, and 66% of patients experienced successful pain control, respectively. There was no significant difference in pain relief in the initial MVD group compared with the initial GKS and initial PRR groups (74% vs 59% and 50%, respectively; p = 0.342). Recurrence of pain was noted in 23 patients. Twelve of these 23 patients underwent another GKS, resulting in pain control in 8 patients (67%); 8 other patients underwent MVD, resulting in pain relief in 7 patients (87.5%). The median time from GKS to pain recurrence was 7 months (range 3-48 months). There was no significant difference in new facial numbness among the 3 groups (p = 0.24); however, in the initial GKS group, facial numbness was significantly associated with freedom from pain (p = 0.0012). There was a significant correlation between the total radiation dose and facial numbness. The cutoff value for facial numbness ranged from 115 to 120 Gy (p = 0.037). CONCLUSIONS Gamma Knife surgery as a second treatment achieved acceptable levels of pain control in 65% of patients with residual or recurrent TN after long-term follow-up. Initial treatment was not a factor that affected pain control, but salvage surgery may be considered separately for each group.

Radiosurgery for vestibular schwannomas.

Background: Radiosurgery has been established as an important alternative to microsurgery. We report our experience with radiosurgery for tumor control and the complications of unilateral vestibular schwannomas. Methods: We reviewed our early experience regarding clinical presentation, management and outcomes in 45 patients with acoustic schwannomas who underwent gamma knife stereotactic radiosurgery. The median follow‐up period was 25 months (range, 6‐48 months). Thirteen patients had undergone 1 or more previous resections before radiosurgery; 32 underwent radiosurgery as the first procedure. Median tumor volume was 4.5 mL (range, 0.5‐30.0), and median radiotherapy dose was 11.5 Gy (range, 10.5‐14.0 Gy). Results: Tumor control was achieved in 43 patients (95.6%). Loss of central contrast enhancement was a characteristic change and was noted in 29 patients (64.4%). Reduction in tumor size was shown in 15 patients (33.3%). Thirteen patients (28.9%) had good or serviceable hearing preoperatively, and in all of these, the preoperative status was retained immediately after radiosurgery. At follow‐up, however, 10 patients (76.9%) had preserved hearing and 3 (23.1%) had reduced hearing on the treated side. Hearing in 1 patient that was not serviceable preoperatively later improved to a serviceable level. No patients had delayed facial palsy or lower cranial nerve dysfunction, but one had delayed trigeminal sensory loss. Conclusion: Radiosurgery achieved a high tumor control rate and a relatively low post‐radiosurgical complication rate for acoustic neuromas.

Apparent diffusion coefficients for evaluation of the response of brain tumors treated by Gamma Knife surgery: Clinical article

OBJECT Cellular density is a major factor for change in the apparent diffusion coefficient (ADC). The authors hypothesized that loss of tumor cells after Gamma Knife surgery (GKS) may alter the ADC value and used diffusion weighted MR imaging (DW imaging) to evaluate cellular changes in brain tumors to detect their treatment response and the efficacy of GKS. METHODS In this paper the authors describe a prospective trial involving 86 patients harboring 38 solid or predominantly solid brain metastases, 30 meningiomas, and 24 acoustic neuromas that were treated by GKS. The patients underwent serial MR imaging examinations, including DW imaging, before treatment and at multiple intervals following GKS. Follow-up MR images and clinical outcomes were reviewed at 3-month intervals for metastatic lesions and at 6-month intervals for benign tumors. Apparent diffusion coefficients were calculated from echo planar DW images, and mean ADC values were compared at each follow-up. RESULTS The mean ADC value for all meningiomas was 0.82 ± 0.15 × 10-3 mm2/sec before GKS. The mean ADC value as of the last mean follow-up of 42 months was 1.36 ± 0.19 × 10-3 mm2/sec, a significant increase compared to that before treatment (p < 0.0001). Calcification (p = 0.006) and tumor recurrence (p = 0.025) significantly prevented a rise in the ADC level.The mean ADC value for all solid acoustic neuromas was 1.06 ± 0.17 × 10-3 mm2/sec before GKS. The mean ADC value as of the last mean follow-up of 36 months was 1.72 ± 0.26 × 10-3 mm2/sec, a significant increase (p =0.0002) compared with values before GKS. At the last mean MR imaging follow-up there appeared to be tumor enlargement in 3 patients (12.5%); however, since the ADC values in these patients were significantly higher than the preradiosurgery values, the finding was considered to be a sign of radiation necrosis rather than tumor recurrence. The mean ADC value of metastatic tumors was 1.05 ± 0.12 × 10-3 mm2/sec before GKS. This value rose significantly(p < 0.0001) to 1.64 ± 0.18 × 10-3 mm2/sec after GKS at a mean follow-up of 9.4 months. Magnetic resonance imaging showed that 89% of these tumors had been controlled by GKS. In 2 patients there were enlarged lesions, but the ADC values were the same as pre-GKS levels, and therefore, the lesions were deemed recurrent. CONCLUSIONS Apparent diffusion coefficient values may be useful in evaluating treatment results before a definitive change in volume is evident on imaging studies. In some patients in whom imaging findings are equivocal, ADC values may also be used to distinguish radiation-induced necrosis from tumor recurrence.(DOI: 10.3171/2010.7.GKS10864)

Use of apparent diffusion coefficients in evaluating the response of vestibular schwannomas to Gamma Knife surgery

OBJECT Cellular density is a major factor responsible for changes in apparent diffusion coefficients (ADCs). The authors hypothesized that loss of tumor cells after Gamma Knife surgery (GKS) might alter ADC values. Magnetic resonance imaging, including diffusion-weighted (DW) imaging, was performed to detect cellular changes in brain tumors so that the authors could evaluate the tumor response to GKS as well as the efficacy of the procedure. METHODS The authors conducted a prospective trial involving 31 patients harboring solid or cystic vestibular schwannomas (VSs) that were treated with GKS. The patients underwent serial MR imaging, including DW imaging, before GKS and at multiple intervals following the procedure. The authors observed the patients over time, evaluating MR imaging findings and clinical outcomes at 6-month intervals. The ADCs were calculated from echo-planar DW images, and mean ADC values were compared at each follow-up. RESULTS The mean follow-up period was 36.5 months (range 18-60 months). Imaging studies showed a reduction in tumor volume in 19 patients (61.3%) and tumor growth arrest in 9 patients (29%). In the remaining 3 patients (9.7%), tumor enlargement was documented at 18, 36, and 42 months. The mean ADC value before GKS for all solid VSs was 1.06 ± 0.17 × 10(-3) mm(2)/second, which significantly increased 6 months after GKS and continued to increase with time (p = 0.0086). The mean ADC value for treated solid tumors as of the last mean follow-up of 36 months (range 18-60 months) was 1.72 ± 0.26 × 10(-3) mm(2)/second (range 1.50-2.09 × 10(-3) mm(2)/second), which was significantly higher than that before GKS (p = 0.0001). Tumor volumes were positively related to ADC values (p = 0.03). The mean ADC value before GKS for all cystic VSs was 2.09 ± 0.24 × 10(-3) mm(2)/second (range 1.80-2.58 × 10(-3) mm(2)/second). The mean ADC value for treated cystic tumors as of the last mean follow-up of 38 months (range 18-48 months) was 1.89 ± 0.22 × 10(-3) mm(2)/second. In 3 patients harboring solid VSs, the tumor enlarged after GKS but the ADC values were higher than those before GKS. The authors considered these tumors to be controlled and continued follow-up in the patients. CONCLUSIONS Apparent diffusion coefficient values may be useful for evaluating treatment results before any definite volume change is detected on imaging studies and for distinguishing radiation-induced necrosis from tumor recurrence in cases in which other imaging results are not definitive, as in cases of increased tumor volume or no volume change. The authors suggest that ADC measurements be included during routine MR imaging examinations for the evaluation of GKS results.

Gamma Knife radiosurgery for large vestibular schwannomas greater than 3 cm in diameter

OBJECTIVE Stereotactic radiosurgery (SRS) is an important alternative management option for patients with small- and medium-sized vestibular schwannomas (VSs). Its use in the treatment of large tumors, however, is still being debated. The authors reviewed their recent experience to assess the potential role of SRS in larger-sized VSs. METHODS Between 2000 and 2014, 35 patients with large VSs, defined as having both a single dimension > 3 cm and a volume > 10 cm3, underwent Gamma Knife radiosurgery (GKRS). Nine patients (25.7%) had previously undergone resection. The median total volume covered in this group of patients was 14.8 cm3 (range 10.3-24.5 cm3). The median tumor margin dose was 11 Gy (range 10-12 Gy). RESULTS The median follow-up duration was 48 months (range 6-156 months). All 35 patients had regular MRI follow-up examinations. Twenty tumors (57.1%) had a volume reduction of greater than 50%, 5 (14.3%) had a volume reduction of 15%-50%, 5 (14.3%) were stable in size (volume change < 15%), and 5 (14.3%) had larger volumes (all of these lesions were eventually resected). Four patients (11.4%) underwent resection within 9 months to 6 years because of progressive symptoms. One patient (2.9%) had open surgery for new-onset intractable trigeminal neuralgia at 48 months after GKRS. Two patients (5.7%) who developed a symptomatic cyst underwent placement of a cystoperitoneal shunt. Eight (66%) of 12 patients with pre-GKRS trigeminal sensory dysfunction had hypoesthesia relief. One hemifacial spasm completely resolved 3 years after treatment. Seven patients with facial weakness experienced no deterioration after GKRS. Two of 3 patients with serviceable hearing before GKRS deteriorated while 1 patient retained the same level of hearing. Two patients improved from severe hearing loss to pure tone audiometry less than 50 dB. The authors found borderline statistical significance for post-GKRS tumor enlargement for later resection (p = 0.05, HR 9.97, CI 0.99-100.00). A tumor volume ≥ 15 cm3 was a significant factor predictive of GKRS failure (p = 0.005). No difference in outcome was observed based on indication for GKRS (p = 0.0761). CONCLUSIONS Although microsurgical resection remains the primary management choice in patients with VSs, most VSs that are defined as having both a single dimension > 3 cm and a volume > 10 cm3 and tolerable mass effect can be managed satisfactorily with GKRS. Tumor volume ≥ 15 cm3 is a significant factor predicting poor tumor control following GKRS.

A Novel Method to Verify Gamma Knife Radioactive Source Count

Background: Regulation requires periodic reconfirmation of the number of radioactive sources in Gamma Knife (GK). To comply with regulations, the total dose output (TDO) method, originally designed to verify amount of radiation received by patients, was adopted as a tool for source security. However, we suspect the TDO method may be unreliable in detecting small numbers of missing sources given that a 2% margin of error is allowed. We propose an alternate method using Gafchromic films to identify number of sources present. Method: To test the efficacy of the TDO method, we simulated real-life source loss by plugging up to 5 sources. TDO after plugging 0, 1, 2, 3, 4, and 5 sources were measured using GK 4C. Percentage change for each additional source plugged was computed. We then proceeded to test the film method. For GK 4C, 2 Gafchromic RTQA2 single sided films measuring 10 × 10 inch were first halved to 5 × 10 inch films. Four 5 × 10 inch films were then adhered to the inner surface of the 18 mm collimator. For GK Perfexion, 2 Gafchromic EBT3 double sided films measuring 10 × 12 inches were combined and rolled into a cone film and adhered to the collimator during installation. In both cases, the films were exposed to 0.5 Gy. Results: TDO was inversely related to the number of source plugged. TDO decreased by more than 2% after 5 plugs. The film method was able to outline all 201 and 192 Co sources for GK4Cand Perfexion respectively. Conclusion: A single lost source is hard to detect using the TDO method given that at least 5 sources had to be lost before the change in TDO will exceed the margin of error (±2%). The film method bypasses this limitation and offers an easy alternative to accurately obtain the number of sources.