title: Precision radiation therapy for optic nerve sheath meningiomas.
abstract: A more precise radiation therapy technique to treat unilateral optic nerve sheath meningioma is presented. It uses an immobilization device to align the ipsilateral optic nerve with a vertical axis and employs three small half-beam blocked fields to deliver radiation to a small conformal volume, thereby reducing the dose to the optic chiasm and the contralateral optic nerve. Three patients were successfully treated with this technique, and a fourth patient with optic nerve glioma was also treated in a similar fashion and was included in this study. The new technique irradiates a much smaller volume of tissue to high dose levels: 58 cm3 is irradiated to the 80% isodose level and only 18 cm3 to the 95% level. In contrast, the opposed lateral technique irradiates 171 and 73 cm3 to these levels, respectively. Thus, a considerable reduction in the volume of normal tissue irradiated was accomplished. Doses to the pituitary and contralateral optic nerve were 4% of the treatment dose for the new technique, whereas these doses were 40% and 100% for opposed laterals and 10% and 3% for wedged pair, respectively. The average setup error for this technique was very small, 50% of the setups measured were less than 1 mm off, and 92.5% were less than 3 mm off. However, for the conventional setups without a mask, only 21% of the setups were less than 1 mm off and 55% less than 3 mm off. We recommend this technique for localized unilateral optic nerve sheath meningioma and other optic nerve lesions that may require radiation therapy.
authors.affiliation: Department of Radiation Oncology, University of California, School of Medicine, San Francisco.
authors.forename: T Y
authors.initials: TY
authors.lastname: Eng
authors.forename: N W
authors.initials: NW
authors.lastname: Albright
authors.forename: G
authors.initials: G
authors.lastname: Kuwahara
authors.forename: C N
authors.initials: CN
authors.lastname: Akazawa
authors.forename: D
authors.initials: D
authors.lastname: Dea
authors.forename: G L
authors.initials: GL
authors.lastname: Chu
authors.forename: W F
authors.initials: WF
authors.lastname: Hoyt
authors.forename: W M
authors.initials: WM
authors.lastname: Wara
authors.forename: D A
authors.initials: DA
authors.lastname: Larson
mesh_terms: D003390:Cranial Nerve Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008577:Meningeal Neoplasms / Q000532:radiotherapy*; D008579:Meningioma / Q000532:radiotherapy*; D009901:Optic Nerve Diseases / Q000532:radiotherapy*; D011878:Radiotherapy / Q000295:instrumentation / Q000379:methods