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Non-skull Base Cranial Meningiomas have a Higher Grade at Recurrence than Skull Base Meningiomas
Proceedings of the 51st Annual ASTRO Meeting
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Carbon Ion Radiotherapy for Skull Base and Paracervical Chordomas
A. Hasegawa, J. Mizoe, K. Jingu, H. Bessho, T. Kamada, H. Tsujii National Institute of Radiological Science, Chiba, Japan Purpose/Objective(s): To estimate the toxicity and efficacy of carbon ion radiotherapy for skull base and paracervical chordomas. Materials/Methods: Between April 1997 and August 2008, a total of 54 patients with skull base or paracervical tumors were treated with carbon ion radiotherapy for phase I/II or phase II clinical trials. The phase I/II dose escalation trial was performed up to the fourthstage dose level (48 GyE, 52.8 GyE, 57.6 GyE and 60.8 GyE). A total carbon ion dose was delivered in 16 fractions over four weeks. From April 2004, a phase II clinical trial was initiated under the Highly Advanced Medical Technology scheme with an irradiation schedule of 60.8 GyE in 16 fractions over four weeks. Thirty-one patients with chordoma were enrolled in these studies and analyzed. Results: The 31 patients consisted of 14 males and 17 females. The age range was from 16 to 76, with a median of 47 years. Median follow-up time was 52 months (range, 9-127 months). At the time of analysis, there was no evidence of any serious acute or late reactions. A late grade 2 brain reaction was detected in 1 patient irradiated with 60.8 GyE, but no other adverse reactions were discovered. The tumor effect remains mostly as stable disease within the six months of carbon ion radiotherapy, and the tumor size showed no dramatic change in most of the cases for a long time. Local control (LC) was defined as showing no evidence of tumor regrowth by MRI, CT, physical examination, or biopsy. In 31 chordoma patients, the five-year LC and overall survival (OS) rates were 78% and 85%, respectively. These patients were divided into two groups; a low-dose group (n = 10) irradiated with doses ranging from 48 to 57.8 GyE and a high-dose group (n = 21) irradiated with 60.8 GyE. The five-year LC rates were 60% for the low-dose group and 93% for the high-dose group. The five-year OS rates were 90% for the low-dose group and 84% for the high-dose group. Although one patient from the high dose group died due to intercurrent hepatic failure, the cause-specific survival rate was 89% for the high-dose group. Conclusions: The carbon ion dose of 60.8 GyE improves local control. Additionally, we did not observe severe toxicity to critical organs such as the brainstem, spinal cord and optic nerves. Author Disclosure: A. Hasegawa, None; J. Mizoe, None; K. Jingu, None; H. Bessho, None; T. Kamada, None; H. Tsujii, None.
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Primary Spinal Cord Glioma: A Surveillance, Epidemiology, and End Results (SEER) Database Study of 1814 Patients
M. T. Milano, M. D. Johnson, J. Sul, N. A. Mohile, D. N. Korones, P. Okunieff, K. A. Walter University of Rochester, Rochester, NY Purpose/Objective(s): To analyze survival outcomes of patients with primary spinal cord glioma, and characterize risk factors affecting outcome. Materials/Methods: 1814 patients with primary spinal cord glioma (excluding patients with primitive neuroectodermal tumors) were analyzed using the SEER database. Univariate analyses (UVA) and multivariate analyses (MVA) were performed. Results: For grade 1 astrocytoma and ependymoma, the 5-year OS was 82% and 92% respectively (p=0.005); the 5-year CSS was 89% and 100% (p = 0.0009). For grade 2 astrocytoma and ependymoma, the 5-year OS was 70% and 97% (p \ 0.00001); the 5-year CSS was 77% and 98% (p = 0.0002). For grade 3 astrocytoma and ependymoma, the 5-year OS was 28% and 58% (p = 0.005); the 5-year CSS was 36% and 64% (p = 0.013). For grade 4 astrocytoma, the 5-year OS was 14% and 5-year CSS was 15%. On UVA of all patients, younger age (p \ 0.00001), more recent decade of diagnosis (p \ 0.00001), white race (p \ 0.03), ependymoma histology (p \ 0.00001), lower grade (p \ 0.00001), greater extent of resection (p \ 0.00001), and no radiotherapy delivery (p \ 0.00001), were significantly favorable predictors of OS and CSS. Gender was not significant. On MVA for OS, all of these variables remained significant aside from the use of radiotherapy, which was borderline significant. On MVA for CSS, all of these variables remained significant aside from race. Additional MVA models were run with tumor size included as continuous variable. Neither tumor size, the use of radiation, nor extent or resection were significant for OS or CSS when tumor size was added to the MVA. Patients with grade 2 ependymoma treated with radiation experienced a worse OS compared to those not treated with radiation, though the CSS was similar. Patients with grade 2 astrocytoma treated with radiation experienced a worse OS and CSS compared to those not treated with radiation. In patients with high grade glioma treated with radiation, there was a non-significant trend towards worse outcome in patients receiving radiation. Conclusions: For patients with primary spinal cord glioma, the variables of age, histology and grade are significant predictors of outcome. Though treatment with radiation was associated with worse outcomes, this likely reflects a selection bias in that patients who were selected to have radiation were more likely to have had adverse risk factors (i.e. larger tumor, close or positive margins). Patients with grade 2 glioma who were selected to not undergo radiation after resection fared quite well with respect to OS and CSS. Given the retrospective nature of this study, specific recommendations about which situations warrant radiation cannot be derived from our analyses. Author Disclosure: M.T. Milano, None; M.D. Johnson, None; J. Sul, None; N.A. Mohile, None; D.N. Korones, None; P. Okunieff, None; K.A. Walter, None.
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Non-skull Base Cranial Meningiomas have a Higher Grade at Recurrence than Skull Base Meningiomas
S. L. McGovern, K. D. Aldape, M. F. Munsell, A. Mahajan, F. DeMonte, S. Y. Woo M.D. Anderson Cancer Center, Houston, TX Purpose/Objective(s): Despite a favorable outcome for most patients with grade I meningiomas, a subset of those patients will have recurrent disease that progresses to a higher grade and requires increasingly aggressive therapy. The goal of this study was to identify clinical characteristics associated with the recurrence of benign meningiomas and their acceleration to atypical and malignant histologies. Materials/Methods: Records of 216 patients with grade I, II, or III meningioma initially treated from 1965 to 2001 were retrospectively reviewed. Median follow-up was 7.2 years. Results: Patients with non-skull base cranial meningiomas were more likely to have a gross total resection than patients with skull-base meningiomas, 78% (82/105) vs. 41% (32/78), p\0.001. Consequently, patients with grade I non-skull base cranial meningiomas had
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better 5-year recurrence-free survival (RFS) than patients with grade I skull-base meningiomas or grade II or III tumors (69% vs. 56% vs. 50%, p = 0.007). Unexpectedly, patients with non-skull base tumors who had a recurrence were more likely than patients with skull base tumors to have a higher grade tumor at recurrence, 36% (8/22) vs. 5% (1/19), p = 0.024. Furthermore, the median MIB-1 of grade I non-skull base cranial meningiomas was significantly higher than that of grade I skull base tumors (2.60% vs. 1.35%, p = 0.016). Conclusions: Cranial meningiomas that occur outside of the skull base are more likely to have a higher MIB-1 and recur with a higher grade than those within the skull base, suggesting that non-skull base cranial meningiomas may have a more aggressive biology than those of the skull base. Author Disclosure: S.L. McGovern, None; K.D. Aldape, None; M.F. Munsell, None; A. Mahajan, None; F. DeMonte, None; S.Y. Woo, None.
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Multisession Stereotactic Radiosurgery for Meningioma Results in Low Rates of Post-treatment Edema
C. E. Lominska, K. Unger, W. C. Jean, J. Chanyasulkit, B. Collins, S. Collins, G. Gagnon Georgetown University Hospital, Washington, DC Purpose/Objective(s): Post-treatment peritumoral brain edema is a known and potentially serious risk of single fraction radiosurgery for meningiomas. Purported high risk factors include increased tumor volume, dose, pre-treatment edema, and tumor location. A recent review, classifying tumor location as basal (e.g.,, cavernous sinus) or nonbasal (e.g.,, parasagittal, convexity), found that edema rates varied from 0-22% with basal lesions, and from 25-71% with nonbasal lesions.1 We review the risk of edema after single fraction and multisession stereotactic radiosurgery. Materials/Methods: We reviewed the records of patients treated for benign and atypical intracranial meningioma at our institution using stereotactic radiosurgery (SRS). 87 lesions were treated in 81 patients from April 2002 to August 2008. Patients were 24 men and 57 women with a mean age of 61 years (range 29-90). 35 patients were treated for recurrence or progression after surgery. 52 lesions were basally located and 35 were non-basal. Mean lesion size was 11.3 mL (0.6-98.2 mL). Radiation was delivered using a frameless robotic stereotactic radiosurgery system in single fraction or multisession treatments (typically 3-5 fractions), with a median of 2500 cGy in 5 fractions. Clinical and radiographic follow-up were reviewed for symptomatic and asymptomatic edema. Results: With a median follow-up of 19 months, 81 lesions were assessable for treatment response. Symptomatic edema developed in 2 cases (2.5%) and asymptomatic edema developed in 3 cases (3.7%). Four of 78 (5%) of the lesions treated with multisession SRS developed edema, one case of which was symptomatic. 4 of 35 (11%) of nonbasal lesions developed edema, whereas 1/52 (2%) of basal lesions developed edema. On univariate analysis, single fraction treatment (p \ 0.05) and nonbasal location (p = 0.08) were significant/borderline significant as risk factors for any edema. Significance was lost on multivariate analysis. For symptomatic edema, pre-treatment edema and single fraction treatment were significant risk factors on multivariate analysis (p \ 0.01 for both). Location, prior radiation, recurrence and volume were not significant. Local control rate was 90% in evaluable patients, with tumor regression in 15 cases (19%). Conclusions: Rates of peritumoral brain edema following multisession SRS were low, even in patients with large tumor volumes and high risk locations. Multisession SRS edema rates may approach the low edema rates seen with conventionally fractionated radiotherapy. Multisession SRS merits consideration in patients at risk for post-treatment edema. 1 Rogers L, Mehta M. Role of radiation therapy in treating intracranial meningiomas. Neurosurgical FOCUS 2007;23:E41-13. Author Disclosure: C.E. Lominska, None; K. Unger, None; W.C. Jean, None; J. Chanyasulkit, None; B. Collins, Accuray, B. Research Grant; Accuray, D. Speakers Bureau/Honoraria; Accuray, F. Consultant/Advisory Board; S. Collins, None; G. Gagnon, Accuray, B. Research Grant; Accuray, D. Speakers Bureau/Honoraria; Accuray, F. Consultant/Advisory Board.
2136
Improve Consistency in Radiation Shot Placement using T1-weighted and FIESTA MRI Sequences in Trigeminal Neuralgia Gamma Knife Radiosurgery
T. J. Wang1, R. Brisman2, J. N. Shah1, E. J. Yoshida1, T. Liu3 1 Department of Radiation Oncology, College of Physicians and Surgeons, Columbia University, New York, NY, 2Department of Neurological Surgery, College of Physicians and Surgeons, Columbia University, New York, NY, 3Department of Radiation Oncology, Emory University, Atlanta, GA Purpose/Objective(s): T1-weighted MRI is most commonly used for treatment planning in trigeminal neuralgia Gamma Knife radiosurgery. Fast imaging employing steady state acquisition (FIESTA) MRI is a newer sequence that provides enhanced visualization of the trigeminal cistern and thus, further distinguishes trigeminal nerve anatomy. The purpose of our study was to assess whether T1-weighted MRI, in combination with FIESTA MRI, can improve consistency in target delineation and precision in radiation shot placement among physicians with varying Gamma Knife radiosurgery experience. Materials/Methods: We studied 10 trigeminal neuralgia patients who received Gamma Knife radiosurgery. T1-weighted and FIESTA MRI sequences were acquired for all patients. For each patient, three physicians with 1, 5, and 12 years of Gamma Knife experience performed target delineation of the symptomatic trigeminal nerve and brainstem, as well as placed a 4-mm radiation shot using (1) T1-weighted MRI alone, (2) FIESTA MRI alone, and (3) combined T1-weighted and FIESTA MRIs. Each physician was blind to the others’ treatment plans. The radiation shot was placed at the root entry zone of the symptomatic trigeminal nerve such that the 50% isodose line touched the brainstem. The volumetric variations of the trigeminal nerve contours and the geometric variations of the shots among physicians were analyzed. Results: Significant variation existed in trigeminal nerve delineation among the physicians, regardless of MRI sequence. Standard deviation of the trigeminal nerve volumes ranged from 2.4 mm3 (4%, standard deviation divided by the mean) to 63.0 mm3 (110%) using T1-weighted MRI alone, 3.3 mm3 (4%) to 12.7 mm3 (84%) using FIESTA MRI alone, and 11.5 mm3 (9%) to 28.5 mm3 (112%) using combined T1-weighted and FIESTA MRIs. For radiation shot placement, the mean geometric variation was 2.3 mm for all imaging methods. However, the standard deviation of shot-placement variation using combined MRI sequences was 42% lower compared to T1-weighted MRI alone, and 36% lower compared to FIESTA MRI alone. Furthermore, 50% fewer cases of shot-placement variation . 5 mm occurred with combined MRI sequences than with T1-weighted MRI alone. We found that patients with poorly visualized trigeminal nerves on T1-weighted MRI benefited most from FIESTA MRI.
2132
Carbon Ion Radiotherapy for Skull Base and Paracervical Chordomas
A. Hasegawa, J. Mizoe, K. Jingu, H. Bessho, T. Kamada, H. Tsujii National Institute of Radiological Science, Chiba, Japan Purpose/Objective(s): To estimate the toxicity and efficacy of carbon ion radiotherapy for skull base and paracervical chordomas. Materials/Methods: Between April 1997 and August 2008, a total of 54 patients with skull base or paracervical tumors were treated with carbon ion radiotherapy for phase I/II or phase II clinical trials. The phase I/II dose escalation trial was performed up to the fourthstage dose level (48 GyE, 52.8 GyE, 57.6 GyE and 60.8 GyE). A total carbon ion dose was delivered in 16 fractions over four weeks. From April 2004, a phase II clinical trial was initiated under the Highly Advanced Medical Technology scheme with an irradiation schedule of 60.8 GyE in 16 fractions over four weeks. Thirty-one patients with chordoma were enrolled in these studies and analyzed. Results: The 31 patients consisted of 14 males and 17 females. The age range was from 16 to 76, with a median of 47 years. Median follow-up time was 52 months (range, 9-127 months). At the time of analysis, there was no evidence of any serious acute or late reactions. A late grade 2 brain reaction was detected in 1 patient irradiated with 60.8 GyE, but no other adverse reactions were discovered. The tumor effect remains mostly as stable disease within the six months of carbon ion radiotherapy, and the tumor size showed no dramatic change in most of the cases for a long time. Local control (LC) was defined as showing no evidence of tumor regrowth by MRI, CT, physical examination, or biopsy. In 31 chordoma patients, the five-year LC and overall survival (OS) rates were 78% and 85%, respectively. These patients were divided into two groups; a low-dose group (n = 10) irradiated with doses ranging from 48 to 57.8 GyE and a high-dose group (n = 21) irradiated with 60.8 GyE. The five-year LC rates were 60% for the low-dose group and 93% for the high-dose group. The five-year OS rates were 90% for the low-dose group and 84% for the high-dose group. Although one patient from the high dose group died due to intercurrent hepatic failure, the cause-specific survival rate was 89% for the high-dose group. Conclusions: The carbon ion dose of 60.8 GyE improves local control. Additionally, we did not observe severe toxicity to critical organs such as the brainstem, spinal cord and optic nerves. Author Disclosure: A. Hasegawa, None; J. Mizoe, None; K. Jingu, None; H. Bessho, None; T. Kamada, None; H. Tsujii, None.
2133
Primary Spinal Cord Glioma: A Surveillance, Epidemiology, and End Results (SEER) Database Study of 1814 Patients
M. T. Milano, M. D. Johnson, J. Sul, N. A. Mohile, D. N. Korones, P. Okunieff, K. A. Walter University of Rochester, Rochester, NY Purpose/Objective(s): To analyze survival outcomes of patients with primary spinal cord glioma, and characterize risk factors affecting outcome. Materials/Methods: 1814 patients with primary spinal cord glioma (excluding patients with primitive neuroectodermal tumors) were analyzed using the SEER database. Univariate analyses (UVA) and multivariate analyses (MVA) were performed. Results: For grade 1 astrocytoma and ependymoma, the 5-year OS was 82% and 92% respectively (p=0.005); the 5-year CSS was 89% and 100% (p = 0.0009). For grade 2 astrocytoma and ependymoma, the 5-year OS was 70% and 97% (p \ 0.00001); the 5-year CSS was 77% and 98% (p = 0.0002). For grade 3 astrocytoma and ependymoma, the 5-year OS was 28% and 58% (p = 0.005); the 5-year CSS was 36% and 64% (p = 0.013). For grade 4 astrocytoma, the 5-year OS was 14% and 5-year CSS was 15%. On UVA of all patients, younger age (p \ 0.00001), more recent decade of diagnosis (p \ 0.00001), white race (p \ 0.03), ependymoma histology (p \ 0.00001), lower grade (p \ 0.00001), greater extent of resection (p \ 0.00001), and no radiotherapy delivery (p \ 0.00001), were significantly favorable predictors of OS and CSS. Gender was not significant. On MVA for OS, all of these variables remained significant aside from the use of radiotherapy, which was borderline significant. On MVA for CSS, all of these variables remained significant aside from race. Additional MVA models were run with tumor size included as continuous variable. Neither tumor size, the use of radiation, nor extent or resection were significant for OS or CSS when tumor size was added to the MVA. Patients with grade 2 ependymoma treated with radiation experienced a worse OS compared to those not treated with radiation, though the CSS was similar. Patients with grade 2 astrocytoma treated with radiation experienced a worse OS and CSS compared to those not treated with radiation. In patients with high grade glioma treated with radiation, there was a non-significant trend towards worse outcome in patients receiving radiation. Conclusions: For patients with primary spinal cord glioma, the variables of age, histology and grade are significant predictors of outcome. Though treatment with radiation was associated with worse outcomes, this likely reflects a selection bias in that patients who were selected to have radiation were more likely to have had adverse risk factors (i.e. larger tumor, close or positive margins). Patients with grade 2 glioma who were selected to not undergo radiation after resection fared quite well with respect to OS and CSS. Given the retrospective nature of this study, specific recommendations about which situations warrant radiation cannot be derived from our analyses. Author Disclosure: M.T. Milano, None; M.D. Johnson, None; J. Sul, None; N.A. Mohile, None; D.N. Korones, None; P. Okunieff, None; K.A. Walter, None.
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Non-skull Base Cranial Meningiomas have a Higher Grade at Recurrence than Skull Base Meningiomas
S. L. McGovern, K. D. Aldape, M. F. Munsell, A. Mahajan, F. DeMonte, S. Y. Woo M.D. Anderson Cancer Center, Houston, TX Purpose/Objective(s): Despite a favorable outcome for most patients with grade I meningiomas, a subset of those patients will have recurrent disease that progresses to a higher grade and requires increasingly aggressive therapy. The goal of this study was to identify clinical characteristics associated with the recurrence of benign meningiomas and their acceleration to atypical and malignant histologies. Materials/Methods: Records of 216 patients with grade I, II, or III meningioma initially treated from 1965 to 2001 were retrospectively reviewed. Median follow-up was 7.2 years. Results: Patients with non-skull base cranial meningiomas were more likely to have a gross total resection than patients with skull-base meningiomas, 78% (82/105) vs. 41% (32/78), p\0.001. Consequently, patients with grade I non-skull base cranial meningiomas had
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better 5-year recurrence-free survival (RFS) than patients with grade I skull-base meningiomas or grade II or III tumors (69% vs. 56% vs. 50%, p = 0.007). Unexpectedly, patients with non-skull base tumors who had a recurrence were more likely than patients with skull base tumors to have a higher grade tumor at recurrence, 36% (8/22) vs. 5% (1/19), p = 0.024. Furthermore, the median MIB-1 of grade I non-skull base cranial meningiomas was significantly higher than that of grade I skull base tumors (2.60% vs. 1.35%, p = 0.016). Conclusions: Cranial meningiomas that occur outside of the skull base are more likely to have a higher MIB-1 and recur with a higher grade than those within the skull base, suggesting that non-skull base cranial meningiomas may have a more aggressive biology than those of the skull base. Author Disclosure: S.L. McGovern, None; K.D. Aldape, None; M.F. Munsell, None; A. Mahajan, None; F. DeMonte, None; S.Y. Woo, None.
2135
Multisession Stereotactic Radiosurgery for Meningioma Results in Low Rates of Post-treatment Edema
C. E. Lominska, K. Unger, W. C. Jean, J. Chanyasulkit, B. Collins, S. Collins, G. Gagnon Georgetown University Hospital, Washington, DC Purpose/Objective(s): Post-treatment peritumoral brain edema is a known and potentially serious risk of single fraction radiosurgery for meningiomas. Purported high risk factors include increased tumor volume, dose, pre-treatment edema, and tumor location. A recent review, classifying tumor location as basal (e.g.,, cavernous sinus) or nonbasal (e.g.,, parasagittal, convexity), found that edema rates varied from 0-22% with basal lesions, and from 25-71% with nonbasal lesions.1 We review the risk of edema after single fraction and multisession stereotactic radiosurgery. Materials/Methods: We reviewed the records of patients treated for benign and atypical intracranial meningioma at our institution using stereotactic radiosurgery (SRS). 87 lesions were treated in 81 patients from April 2002 to August 2008. Patients were 24 men and 57 women with a mean age of 61 years (range 29-90). 35 patients were treated for recurrence or progression after surgery. 52 lesions were basally located and 35 were non-basal. Mean lesion size was 11.3 mL (0.6-98.2 mL). Radiation was delivered using a frameless robotic stereotactic radiosurgery system in single fraction or multisession treatments (typically 3-5 fractions), with a median of 2500 cGy in 5 fractions. Clinical and radiographic follow-up were reviewed for symptomatic and asymptomatic edema. Results: With a median follow-up of 19 months, 81 lesions were assessable for treatment response. Symptomatic edema developed in 2 cases (2.5%) and asymptomatic edema developed in 3 cases (3.7%). Four of 78 (5%) of the lesions treated with multisession SRS developed edema, one case of which was symptomatic. 4 of 35 (11%) of nonbasal lesions developed edema, whereas 1/52 (2%) of basal lesions developed edema. On univariate analysis, single fraction treatment (p \ 0.05) and nonbasal location (p = 0.08) were significant/borderline significant as risk factors for any edema. Significance was lost on multivariate analysis. For symptomatic edema, pre-treatment edema and single fraction treatment were significant risk factors on multivariate analysis (p \ 0.01 for both). Location, prior radiation, recurrence and volume were not significant. Local control rate was 90% in evaluable patients, with tumor regression in 15 cases (19%). Conclusions: Rates of peritumoral brain edema following multisession SRS were low, even in patients with large tumor volumes and high risk locations. Multisession SRS edema rates may approach the low edema rates seen with conventionally fractionated radiotherapy. Multisession SRS merits consideration in patients at risk for post-treatment edema. 1 Rogers L, Mehta M. Role of radiation therapy in treating intracranial meningiomas. Neurosurgical FOCUS 2007;23:E41-13. Author Disclosure: C.E. Lominska, None; K. Unger, None; W.C. Jean, None; J. Chanyasulkit, None; B. Collins, Accuray, B. Research Grant; Accuray, D. Speakers Bureau/Honoraria; Accuray, F. Consultant/Advisory Board; S. Collins, None; G. Gagnon, Accuray, B. Research Grant; Accuray, D. Speakers Bureau/Honoraria; Accuray, F. Consultant/Advisory Board.
2136
Improve Consistency in Radiation Shot Placement using T1-weighted and FIESTA MRI Sequences in Trigeminal Neuralgia Gamma Knife Radiosurgery
T. J. Wang1, R. Brisman2, J. N. Shah1, E. J. Yoshida1, T. Liu3 1 Department of Radiation Oncology, College of Physicians and Surgeons, Columbia University, New York, NY, 2Department of Neurological Surgery, College of Physicians and Surgeons, Columbia University, New York, NY, 3Department of Radiation Oncology, Emory University, Atlanta, GA Purpose/Objective(s): T1-weighted MRI is most commonly used for treatment planning in trigeminal neuralgia Gamma Knife radiosurgery. Fast imaging employing steady state acquisition (FIESTA) MRI is a newer sequence that provides enhanced visualization of the trigeminal cistern and thus, further distinguishes trigeminal nerve anatomy. The purpose of our study was to assess whether T1-weighted MRI, in combination with FIESTA MRI, can improve consistency in target delineation and precision in radiation shot placement among physicians with varying Gamma Knife radiosurgery experience. Materials/Methods: We studied 10 trigeminal neuralgia patients who received Gamma Knife radiosurgery. T1-weighted and FIESTA MRI sequences were acquired for all patients. For each patient, three physicians with 1, 5, and 12 years of Gamma Knife experience performed target delineation of the symptomatic trigeminal nerve and brainstem, as well as placed a 4-mm radiation shot using (1) T1-weighted MRI alone, (2) FIESTA MRI alone, and (3) combined T1-weighted and FIESTA MRIs. Each physician was blind to the others’ treatment plans. The radiation shot was placed at the root entry zone of the symptomatic trigeminal nerve such that the 50% isodose line touched the brainstem. The volumetric variations of the trigeminal nerve contours and the geometric variations of the shots among physicians were analyzed. Results: Significant variation existed in trigeminal nerve delineation among the physicians, regardless of MRI sequence. Standard deviation of the trigeminal nerve volumes ranged from 2.4 mm3 (4%, standard deviation divided by the mean) to 63.0 mm3 (110%) using T1-weighted MRI alone, 3.3 mm3 (4%) to 12.7 mm3 (84%) using FIESTA MRI alone, and 11.5 mm3 (9%) to 28.5 mm3 (112%) using combined T1-weighted and FIESTA MRIs. For radiation shot placement, the mean geometric variation was 2.3 mm for all imaging methods. However, the standard deviation of shot-placement variation using combined MRI sequences was 42% lower compared to T1-weighted MRI alone, and 36% lower compared to FIESTA MRI alone. Furthermore, 50% fewer cases of shot-placement variation . 5 mm occurred with combined MRI sequences than with T1-weighted MRI alone. We found that patients with poorly visualized trigeminal nerves on T1-weighted MRI benefited most from FIESTA MRI.