Stereotactic Gamma Knife Raiodusrgery For Vestibular Schwannoma Ming-Hsi Sun Hung-Chuan PanChiung-Chyi Shen Neurosurgery Taichung Veterans General Hospital Neuroscience combined conference

The first prototype of Leksell Gamma Knife® was installed in Stockholm, Sweden. The delivery of a single, high dose of irradiation to a small and critically located intracranial volume through the intact skull

Protective shielding Spherical collimator helmet Leksell Stereotactic System® Isocenter/ Target in the brain Automatic Positioning System™ 201 sources of radiation

Bony wall of Internal acoustic canal Superior vestibular nerveFacial nerve Cochlear nerve Vestibular tumor arising from Inferior vestibular nerve 50% isodose line Depiction of the internal auditory canal and its content in the sagittal plane Inferior vestibular nerve

Selectivity in radiosurgery Selectivity - describes how well a desired biological effect is achieved in a target volume without complications. targetbiological effect =

Conformity of dose to target The two pictures show the necessity for multiple isocenters in order to minimize dose delivered to normal tissue. target

Selectivity & Conformity Conformity describes only how well the prescription dose is fitted to the target volume, whereas selectivity also takes irradiation to normal tissue into account. Conformal Conformal and selective

Gamma Knife® surgery

Indications for Gamma Knife ® surgery Vascular disorders (15%) Benign tumors (35%) Malignant tumors (42%) Functional disorders (7%) Ocular disorders (1%) Vascular Disorders AVM Aneurysm Cavernous Angiomas Other Vascular Benign Tumors Vestibular Schwannoma Trigeminal Schwannoma Other Schwannoma Benign Glial Tumors (Grade I+II) Meningioma Pituitary Adenoma (Secreting) Pituitary Adenoma (Non-secreting) Pineal Region Tumor Hemangioblastoma Hemangiopericytoma Craniopharyngioma Chordoma Glomus Tumor Other Benign Tumors Malignant Tumors Malignant Glial Tumor (Grade III+IV) Metastatic Tumor Chondrosarcoma NPH Carcinoma Other Malignant Tumors Functional Disorders Trigeminal Neuralgia Parkinson's Disease Intractable Pain Epilepsy OCD Other Functional Ocular Disorders Uveal Melanoma Glaucoma Other Ocular Disorder Source: Leksell Gamma Knife Society, June 2004

Neurilemmomas Vestibular n. 12* Trigeminal n. 3 Faical n. 1 Hypoglossal n. 2 Total 18 July April 2006 follow up > 12 months in VGHTC * Two cases of Neurofibromatosis type II

Treatment Plan : Dose –volume Mean Margin Dose Gy Mean Max. Dose Gy Isodose % at margin Ave. Tx volume CC Neurilemmoma %5.35 (11-13)(22-30)(40-50%)( )

y/o M Gamma knife on Gy at 50% /4.4 CC

Radiographic follow-up Tumor volumedecreaseStable EnlargeFailure Control rate Acoustic Neurilemmoma (12) 4611*91.6%  5 cases in hearing function (audiometry : 1 improvement, 1 worsening, 3 stable )  Facial nerve function preservation :all *One large acoustic neuroma underwent surgical resection 6 months after GKS due to persistent dizziness and imbalance

y/o F 11 Gy at 40% /19.7CC

62 y/o F Surgical resection Gy, 40% isodose ; 20 CC

Microsurgery Retrosigmoid ( Suboccipital ) Approach Transslabyrinthine Approach Middle Cranial Fossa Approach

Functional Outcome of Microsurgery Facial function Overall 80% H-B grade I-II Size 90% ; >4 cm 40-50% Hearing impairment Overall 30-80% preservation 8-57% retrosigmoid approach 32-68% middle fossa approach Tinnitus Post-op immediate new symptom 30-50% Worse 6-20%; No change: most cases; improve 25-60% Complications CSF leakage : 2-20% ; % retrosigmoid approach Death 0.5% ICH: 1-2% Subcutaneous hematoma 3% Cerebellar, brainstem edema 1.2% Hemiparesis 1.2% Meningitis 1.2% Cranialnerve paresis 1-2% Recurrent rate 5-10%

StudyNo. Patients% of local controlFacial nerve morbidityLoss of hearing Lunsford LD, %1%21% Regis J, %1.3%2.2% Landy HJ, %0% Rowe JG, %1%25% Iwai Y, %0%41% Unger F, %2%45% Litvack ZN, %0%38% Petit JH, %0%12% Bertallanfy A, %12.5%21% Prasad D, %2%35% Liscak R, %1.9%17% Kwon Y, %5%35% Noren G, %2%30% Radiosurgery

Treatment of choice Source: Neurosurgery 1998; 43/3 ( ). Pollock B.E., Lunsford L.D., Norén G. “Vestibular Schwannoma Management in the Next Century: A Radiosurgical Perspective” Number of Cases Gamma Knife® Surgery Microsurgery

Tumor diameter > 3 cm Symptomatic brainstem compression Management Algorithm for Acoustic Tumors Tumor Size, Brainstem Compression Intracanalicular tumor Tumor diameter < 3 cm No or mild brainstem compression Age,Health Review of Treatments, Goals Patient’s choice > 75 yr< 75 yr Observation Tumor growth Radiosurgery Residual or Recurrent tumor Observation Microsurgery Residual tumor Complete resection Radiosurgery Tumor growth Radiosurgery Practice Guideline By L. Dade Lunsford; Ajay Niranjan IRSA