Gamma knife radiosurgery for malignant melanoma in the orbit in japanese population

Keywords: melanoma, gamma knife, orbit, radiosurgery, outcome

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     Malignant melanoma (MM) in the orbit is a rare clinical entity especially in Japan.
     Here we examined the usefulness of Gamma Knife radiosurgery (GKRS) for the treatment of MM in the orbit among Japanese population.
     Between July 1998 and March 2006, 6 patients (Male/Female=3/3) with MM in the orbit were treated by GKRS. One was MM in the retrobulbar orbit and the others were uveal melanoma. The age of patients was between 21 and 77 with the average of 51.
     Patients with MM in the orbit those who were treated primarily by GKRS at Shin-Koga Hospital GK Center and more than 5 years ago were included in this retrospective analysis.
     The volume of tumor was between 0.19 and 5.8cc with the average of 0.40cc. Prescribed dosage of 45Gy at 47-50% isodose and 25Gy at 50% isodose were delivered onto uveal melanoma amd MM in the retrobulbar orbit, respectively. Follow up periods were between 5 and 116 months with the average of 65 months. Two patients have died. One has died due to liver metastasis at 5 months after GKRS, and the other was due to unrelated lung cancer at 37 months after GKRS. The incidence of vitreous hemorrhage, neovascular glaucoma, and retinopathy were 4/6 (67%), 2/6 (33%), and 3/6 (50%), respectively. Enucleation was necessary due to uncontrollable neovascular glaucoma in one case. Photocoagulation was performed in 2 cases due to retinopathy. Local tumor control rate was 100%, however, no usable visual acuity was preserved later than 2 years after GKRS. Mild enophthalmos has developed at 104 months after GKRS in one patient.
     This was a retrospective study.
     GKRS is a useful tool to treat MM in the orbit among Japanese population, especially from the cosmetic point of view.
     Tight follow up is necessary to handle ophthalmological complications. Longer follow up is necessary to obtain a definitive conclusion.


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