Ocular and orbital lesions

Treatment of orbital and ocular lesions using radiosurgery faces a number of technical and dosimetric challenges. Fixation of the orbit is a challenge as is the potential for image distortion given the eccentric location of the target. This location also can impact dose calculations. Stereotactic radiosurgery (SRS) is attractive, however, because of the ability to deliver highly conformal radiation doses with great accuracy. Both Gamma Knife and Linac systems have been used successfully. Uveal melanomas are typically treated with doses between 25 and 45 Gy while attempting to keep the optic nerve dose below 10 Gy. Similarly metastases can be treated using the same techniques. Non-oncologic indications include age-related macular degeneration (ARMD) and glaucoma. Gamma Knife has been shown effective at diminishing subretinal neovascularization in ARMD. The mechanism of action in alleviating pain in glaucoma is not yet understood.