Radiosurgery using the Leksell Gamma Knife (LGK) applied to ophthalmologic indications is a specific area where the eye target has a very eccentric location, since the eye can move, its fixation is required and the patient is generally treated in a prone position. It was demonstrated that the LGK is sufficiently accurate to be used for ophthalmic radiosurgery. Current spectrum of treated indications includes uveal melanomas, eye metastases, advanced glaucoma, age-related macular degeneration (ARMD), hemangioblastoma, angioreticuloma, pseudotumors and vegetative pain. The results for uveal melanomas are recognized and the value of the LGK in the treatment of glaucoma and ARMD seems promising after initial studies. Gamma Knife radiosurgery of the ciliary body leads to a significant alleviation of pain and reduction in intraocular pressure in advanced glaucoma. The latency of the treatment effect is relatively short. In the majority of patients with ARMD, both ultrasonography and fluorescein angiography demonstrated a regression of the neovascular complex or stabilization after LGK radiosurgery. A number of rare ophthalmologic indications have also been treated by the Gamma Knife in our Center with more or less prominent therapeutic responses.
The prescription dose to the tumor margin ranged between 50 to 70 Gy with a maximum dose between 90 to 120 Gy. J Neurosurg (Suppl 3) 93: 184–188, 2000 Gamma-knife-based stereotactic radiosurgery for uveal melanoma. Fakiris AJ , Lo SS , Henderson MA , Witt TC , Worth RM , Danis RP , Des Rosiers PM , Timmerman RD . Department of Radiation Oncology, Indiana University Medical Center, Indianapolis, USA. Nineteen patients with uveal melanoma were treated with Gamma-Knife-based stereotactic radiosurgery (SRS). The radiation dose was 40 Gy prescribed to the 50% isodose line for all patients. The median follow-up was 40 months. The 3- and 5-year overall survival rates were 86 and 55%, respectively. The 3- and 5-year tumor control rates were both 94%. Six of the 19 treated patients (32%) developed distant metastasis 31-75 months after SRS. Out of the 19 patients treated with SRS, 2 had improved, 4 had stable and 13 had worse vision in the treated eye. Gamma-Knife-based SRS appears to provide excellent local control of uveal melanoma. The risk of distant metastasis is significant. Effective systemic therapy is to be explored to improve the treatment outcome of uveal melanoma. Copyright (c) 2007 S. Karger AG, Basel.
Purpose of this study was to assess different aspects of ophthalmic radiosurgery accuracy performed on the Leksell Gamma Knife (ELEKTA Instrument, Sweden): (1) accuracy of magnetic resonance imaging (MRI) for the eye, (2) stability and rigidity of eye fixation, (3) accuracy of the Leksell GammaPlan (ELEKTA Instrument, Sweden) treatment planning system calculations and (4) treatment delivery by the Leksell Gamma Knife. It was demonstrated in this study that Leksell Gamma Knife can be used for ophthalmic radiosurgery with sufficient accuracy. Stability of eye fixation and geometric accuracy of MRI can be achieved with careful quality control. Siemens EXPERT (Siemens, Germany) 1T MRI scanner was found to be better for eye imaging compared to Siemens SYMPHONY (Siemens, Germany) 1.5 T in terms of geometric accuracy. Coronal MRI slices demonstrated higher image distortion and were not accepted for eye imaging. Three-dimensional gradient echo image sequence with 1.3 mm slice thickness was selected for a standard imaging procedure for eye lesions. Eye fixation technique used in this study was achieved by retrobulbar local anesthesia and applying two sutures in the rectus muscles and attaching these sutures to the Leksell stereotactic frame. This eye fixation technique showed very good stability and rigidity in time, patient prone versus supine position had no effect on stereotactic target and eye structures localization. Treatment planning system calculations for relative doses demonstrated good agreement with measured data. Absolute doses measured by pinpoint ion chamber at depths of 10mm and deeply showed relatively good agreement with the treatment planning system calculated data (delivered doses were systematically lower than calculated ones usually within 3-5%). Absolute doses measured by pinpoint ion chamber in depths less than 10mm showed relatively large deviation compare to the treatment planning system calculated data (delivered doses were systematically lower than calculated ones of about 15-20%). One should be aware of this, especially when reporting doses for structures as eye lid, eye lens and etc. Calculation errors can be probably reduced by a sufficient volume of a proper built-up material fixed on a patient eye.
J Neurosurg . 2005 Jul;103(1):192; author reply 192-3. Progress in glaucoma treatment research: a nonrandomized prospective study of 102 patients with advanced refractory glaucoma treated by Leksell gamma knife irradiation. Vladyka V , Liscak R , Simonova G , Pilbauer J , Hejdukova I , Novacek L . Department of Stereotactic and Radiation Neurosurgery, Na Homolce Hospital, Prague, Czech Republic. email@example.com OBJECT: The authors performed a study to characterize the effects of ciliary body gamma knife surgery (GKS) for advanced glaucoma. METHODS: In addition to a pilot project involving 14 patients, 88 other patients were treated. Four 8-mm isocenters were used. Blind eyes received 20 Gy to the 50% isodose. If there was preserved vision the dose was 15 Gy. The median follow up was 20 months (range 2-54 months). Severe pain was present in 93% of patients with secondary glaucoma; after GKS it was substantially improved in 89% of cases. In primary open angle glaucoma, the pain was less frequent and severe. In more than half the patients it disappeared during a median latency of 6 weeks. The median intraocular pressure value was lowered in patients with secondary glaucoma (from 51.3-27 mm Hg). The same values for primary glaucoma were 25.3 and 16.1 mm Hg, respectively, after a median latency of 12 weeks. Twenty-seven of 40 patients with neovascular glaucoma showed a marked reduction of neovascularization after a median latency of 18 weeks. Treatment complications were slight. There was postoperative lacrimation in 61%. Two patients underwent postirradiation cataract extraction. Noninfectious keratitis was observed in two patients. Pharmacotherapy could be reduced in all patients and ceased in approximately one third. There has been no recurrence of the initial symptoms and no worsening of visual acuity. CONCLUSIONS: Gamma knife surgery ameliorates the main symptoms in advanced glaucomas and precludes the need for eventual ocular enucleation. PMID: 15662813 [PubMed - indexed for MEDLINE]
Ophthalmic indications of_gk
OPHTHALMIC INDICATIONS: GK SURGERY Dr Deepak Agrawal Assistant Professor, Department of Neurosurgery & Gamma Knife, All India Institute of Medical Sciences, New Delhi
EYE IMMOBILIZATION <ul><li>Retrobulbar anesthetic block of 2.5 ml mepivacain and 2.5 ml bupivacaine </li></ul><ul><li>Transconjunctival fixation of the four rectus muscles and fixation of the sutures to the stereo-tactic frame </li></ul>
POSITIONING <ul><li>The radiosurgical procedure is usually performed with the patient in the prone position </li></ul>
UVEAL MELANOMA <ul><li>Fakiris AJ et al. Gamma-knife-based stereotactic radiosurgery for uveal melanoma. Stereotact Funct Neurosurg. 2007;85(2-3):106-12 </li></ul><ul><li>40 Gy prescribed to the 50% isodose line for all patients </li></ul><ul><li>The 3- and 5-year tumor control rates were both 94% </li></ul>
ACCURACY <ul><li>Novotný J, Novotný J, Lišcák R, Spevácek V, Hrbácek J, Dvorák P, Cechák T, Tintera J, Vymazal J, Vladyka V. Assessment of the Accuracy in Ophthalmic Radiosurgery . Kondziolka D (ed): Radiosurgery. Basel, Karger, 2006, vol 6, pp 71-85 </li></ul>