Long term evaluation of optic nerve dose and radiation optic neuropathy in gamma knife radiosurgery

Jacqueline Leavitt1, Scott Stafford1, Michael Link1, Bruce Pollock2

1Rochester, United States 2Mayo Clinic Rochester, Rochester, USA

Keywords: optic nerve, adverse radiation effect, gamma knife, vision, radiosurgery

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     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 ()