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Gamma Knife radiosurgery controls local tumors in choroidal melanoma
Gamma Knife radiosurgery for choroidal melanoma yielded visual outcomes similar to those of linear accelerator-based fractionated stereotactic radiotherapy, according to a study.
The retrospective study included 177 patients with choroidal melanoma who underwent treatment with Gamma Knife radiosurgery between 1992 and 2010.
Investigators assessed preservation of baseline visual acuity of 20/40 or better, 20/200 or better, or counting fingers or better, and they analyzed patient-, tumor- and treatment-related data as possible risk factors for loss of vision from choroidal melanoma. The median follow-up interval was 39.5 months.
Results showed that 5 years after treatment, the probability of maintaining visual acuity of 20/40 or better was 13%, 20/200 or better was 14%, and counting fingers or better was 36%.
Deterioration of vision after treatment occurred in 84.7% of patients.
The leading risk factors for loss of vision were tumor height, longest basal diameter, distance to the optic disc or foveola, and incidence of previous retinal detachment.
Tumors recurred in 10 patients a median 13.6 months after treatment. However, local tumors were controlled in 94.4% of cases.
Perspective
Back to TopRadiotherapy for uveal melanoma is generally regarded as the reasonable treatment option. The Collaborative Ocular Melanoma Study concluded that plaque radiotherapy was equivalent to enucleation for melanoma control with medium-size tumors. Based on this finding, most patients prefer eye-salvaging methods to protect the globe and ultimate vision. However, the problem of every conservative treatment is long-term visual acuity loss.
Most ocular melanoma centers in the United States use plaque radiotherapy (brachytherapy) or proton beam radiotherapy (teletherapy) in the management of melanoma. Gamma Knife radiosurgery is a form of teletherapy in which approximately 200 beams of radiation are focused on the tumor for a cumulative single-day dose equivalent to 5 days of plaque or proton beam radiotherapy. The major benefit is the short time to deliver the dose — 1 day. Another benefit is precision with little collateral damage. But similar results can be achieved with plaque radiotherapy and proton beam radiotherapy. The main downside of Gamma Knife treatment is the need for fixation of the radiation helmet to the cranium with surgical screws. More recent innovations in radiosurgery allow radiation without cranium fixation using the cyberkife technique.
In this study, the high tumor control rate (94%) is balanced by the anticipated loss of vision to 20/200 or worse (85%). The rate of visual loss is similar to plaque radiotherapy and proton beam radiotherapy. This method represents a useful alternative for patients with uveal melanoma who wish to avoid enucleation.