Long term evaluation of optic nerve dose and radiation optic neuropathy in gamma knife radiosurgeryJacqueline Leavitt1, Scott Stafford1, Michael Link1, Bruce Pollock21Rochester, United States 2Mayo Clinic Rochester, Rochester, USA Keywords: optic nerve, adverse radiation effect, gamma knife, vision, radiosurgery
Visual outcomes are important in brain tumor management.
Our purpose was to determine the long-term risk of radiation-related optic neuropathy (RON) in patients having Gamma Knife radiosurgery (GKRS) for benign skull base tumors.
From 1991-1999, 222 patients underwent GKRS for confirmed WHO Grade 1 or presumed meningiomas (n=143), pituitary adenomas (n=72) or craniopharyngiomas (n=7). Excluded were patients with prior external beam radiation therapy. Prior surgery was performed in 129 patients (58%).
Dose planning was performed using MRI in all cases. A median of 9 isocenters (range, 1-29) were used to treat a median tumor volume of 5.9 cm3 (range, 0.1-30.4). The median tumor margin dose was 18 Gy (range, 12-30). The maximum radiation dose to the optic chiasm and nerves was initially calculated by interpolation of isodose curves on the anterior visual pathways (AVP) (1991-1993), then maximum point dose determination (1994-1999) using Gamma Plan. Maximum AVP dose: < 8.0 Gy (n=126), 8.1-10.0 Gy (n=39), 10.1-12 Gy (n=47), > 12 Gy (n=10). The mean clinical and imaging patient follow-up was 83 months (range, 4-238) and 123 months (range, 8-237), respectively.
In these patients with up to 19 years of follow-up, one patient (0.5%) developed RON. This patient had undergone prior surgery and had documented optic atrophy before GKRS. Eighteen months after GKRS she developed unilateral visual field loss; the AVP dose was 12.8 Gy. The risk of RON for patients receiving > 8 Gy to the AVP was 1.0%.
This was a retrospective study.
Patient selection, conformal dose planning and appropriate dose prescription are necessary to achieve tumor control at a low risk of RON.
Selected cases can be treated safely with maximum AVP doses of 10-12Gy with low risk of developing RON. Project Roles:
J. Leavitt (), S. Stafford (), M. Link (), B. Pollock ()