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György T. Szeifert, Nicolas Massager, Jacques Brotchi and Marc Levivier

possible treatment modalities is radiosurgery, either as a primary intervention for circumscribed, small-volume, deep-seated lesions with difficult surgical access, or as a complementary treatment to other therapy. 10, 19, 20 Astrocytic tumors usually present with histologically more malignant characteristics at the time of recurrence, even if the original picture was relatively benign. 9 Postirradiation recurrent tumors may demonstrate alterations in gene expression, 7 which generally results in a dedifferentiated phenotypic appearance. We describe a patient with

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Marc Levivier, Rafael E. Carrillo, Rémi Charrier, André Martin and Jean-Philippe Thiran

T he Leksell Gamma Knife (LGK, Elekta AB) is a dedicated device for cranial radiosurgery using concomitant gamma rays emitted from 60 Co radiation sources focusing at an isocenter. This design provides unique dosimetry characteristics with a very steep gradient. 10 , 13 , 17 , 18 Usually, multiple isocenters are used to shape the desired irradiation to the target volume with a high conformity and selectivity. Manual forward planning (i.e., the user places each isocenter at specific stereotactic coordinates) is currently the standard, most frequent way to plan

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effects are dependent not only on distance, but also on the dose, rate of administration, and the volume injected. 6 A dose administered as a bolus is more likely to produce central side effects than the same dose given as a slow continuous infusion. The efficacy and safety of intrathecal baclofen for long-term control of spasticity are well established. Interest in functional outcome and quality of life issues in patients with spasticity or other neurological disabilities has exposed the limitations of the currently available objective scales. There is a need for

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Benoit J. M. Pirotte, Alphonse Lubansu, Nicolas Massager, David Wikler, Serge Goldman and Marc Levivier

emission tomography with [ 18 F]fluoro-2-deoxy-D-glucose in the low-grade glioma . Neurosurgery 39 : 470 – 476 , 1996 6 Fisher BJ , Bauman GS , Leighton CE , Stitt L , Cairncross JG , Macdonald DR : Low-grade gliomas in children: tumor volume response to radiation . J Neurosurg 88 : 969 – 974 , 1998 7 Fisher PG , Fisher PG , Breiter SN , Carson BS , Wharam MD , Williams JA , : A clinicopathologic reappraisal of brain stem tumor classification. Identification of pilocystic astrocytoma and fibrillary astrocytoma as distinct

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Nicolas Massager, José Lorenzoni, Daniel Devriendt, Françoise Desmedt, Jacques Brotchi and Marc Levivier

mild intravenous sedative had been administered in a standard manner. The frame was applied as close as possible to the plane of the intracisternal trigeminal nerve root. In all patients, we obtained stereotactic axial T 1 -weighted MR images, without and with Gd-contrast enhancement, and three-dimensional T 2 -weighted volume acquisitions divided in 1-mm slices, followed by CT densitometric imaging acquisition. Treatment planning was performed using Leksell GammaPlan (Version 5.31; Elekta Instruments AB). Fusion of the MR and CT images was performed to visualize the

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Constantin Tuleasca, Laura Negretti, Mohamed Faouzi, Vera Magaddino, Thierry Gevaert, Erik von Elm and Marc Levivier

R adiosurgery was invented by the Swedish neurosurgeon Lars Leksell at the beginning of the 1950s 19 and defined as the “delivery of a single, high dose of ionizing radiation to a small and critically located intracranial volume through the intact skull.” 19 The main principle is that the radiation dose is concentrated within the target (conformity) while minimizing the irradiating of the surrounding healthy tissue, due to a very steep gradient (selectivity). Originally, Leksell conceived radiosurgery as a primary tool for functional disorders. 18 , 19 In the

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Jean Régis, Constantin Tuleasca, Noémie Resseguier, Romain Carron, Anne Donnet, Jean Gaudart and Marc Levivier

may involve a mechanism of action that is more subtle than a purely destructive one. The technical nuances of GKS have a major impact on the clinical outcome of radiosurgery for TN. 33 Pain control increases according to the dose prescription, but a larger volume of nerve treated has been reported to dramatically increase the toxicity (i.e., the risk of bothersome hypesthesia) without increasing the rate of pain relief. 8 Also, a target placed close to the brainstem at the level of the root entry zone 26 seems to be associated with a higher risk of numbness and

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György T. Szeifert, Nicolas Massager, Daniel DeVriendt, Philippe David, Françoise De Smedt, Sandrine Rorive, Isabelle Salmon, Jacques Brotchi and Marc Levivier

been GKS. Dose planning was based on MR imaging and computerized tomography scanning with additional metabolic data obtained using positron emission tomography in some cases. 8 The treated volume ranged from 6.5 to 15.6 cm 3 . The tumors received a prescription dose of 9 to 16 Gy delivered to the target margin in the 50% isodose. The maximum dose ranged between 18 and 32 Gy. The relevant lesions were removed during conventional craniotomy after discovery of progression of neurological deficit 3 to 12 months after radiosurgery. The surgical exploration required the

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Nicolas Massager, Ouzi Nissim, Carine Delbrouck, Isabelle Delpierre, Daniel Devriendt, Françoise Desmedt, David Wikler, Jacques Brotchi and Marc Levivier

fibers (eighth cranial nerve damage); compression or thrombosis of the internal auditory artery, leading to ischemic injury of the cochlea; or direct radiation injury to inner ear structures. 1 It has been shown that the components of the cochlea are likely to be damaged by radiation exposure after fractionated radiation therapy. 6 Although the purpose of radio-surgery is to deliver a high dose of radiation with a steep gradient into the tumor volume, structures located near the irradiated target will nevertheless receive a significant amount of radiation. Therefore

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György T. Szeifert, Isabelle Salmon, Sandrine Rorive, Nicolas Massager, Daniel Devriendt, Stephan Simon, Jacques Brotchi and Marc Levivier

better tumor control after radiosurgery, in that the interval from GKS to surgery was over 6 months. In the five patients in whom this applied, sharply demarcated areas of coagulation necrosis were surrounded by differing amounts of granulation tissue rich in collagen bundles together with small vessels (that is, arterioles, capillaries, and venules). The granulation tissue reaction was accompanied by a striking inflammatory cell infiltration, which varied across the volume of the GKS-induced lesions. The necrotic center of the lesions consisted of tissue debris mixed