Abstract

Objectives: Hypofractionated stereotactic radiation has been our standard treatment option for selected peri-papillary ocular melanomas not amenable to Ru-106 or I-125 plaque brachytherapy. Since 2010 we have migrated the treatment of these patients to our Cyberknife unit. We aim to report our technical experience with this new stereotactic radiotherapy technique. Methods: We retrospectively analyzed 7 patients treated on the Cyberknife radiosurgery system of the Centre Hospitalier de l’Université de Montréal with a Cyberknife from October 2010 to September 2011. All patients had non-metastatic peripapillary choroidal melanomas with no evidence of extrascleral tumor extension at initial ultrasound. A custom device with light and camera was designed to maintain and monitor the position of the treated eye. Tumors were delineated with the help of MRI co-registration and clinical (fundoscopy, ultrasound) reports — a combined CTV/PTV margin of 2.5-3 mm was applied. The planned dose for all patients was 60Gy in 10 daily fractions. Results: Six patients were treated for a newly diagnosed ocular melanoma and one patient was treated for a marginal failure of plaque brachytherapy. The median age for patients was 51 years (range: 24-67). Three patients were staged to have small melanomas according to the Collaborative Ocular Melanoma Study, while four had medium tumors. The median gross tumor volume (GTV) was 0.3 cm3 (range: 0.1 – 0.4 cm3), whereas the median planning tumor volume (PTV) was 1.0 cm3 (range: 0.5 – 2.8 cm3). Three patients were treated with a single 7.5mm collimator, two with 10mm and two with 12.5 mm. The median minimum and mean GTV doses were 62.2 Gy (range: 59.2 - 67.9 Gy) and 70.1 Gy (range: 68.5 - 75.9 Gy). The median minimum and mean doses to the PTV were 54.46 Gy (range: 51.9 - 59.8 Gy) and 66.44 Gy (range: 64.3 - 69.0 Gy). The mean PTV coverage was 95.1% (SD 3.5%) while the mean new conformity index was 1.3 (range: 1.2 -1.4). The median maximum doses to organs at risk were: 3.9 Gy (range: 2.4 – 5.6 Gy) for the ipsilateral lens, 60.9 Gy (range: 59.9 – 63.9 Gy) for the ipsilateral optic nerve, 33.2 Gy (range: 16.9 – 69.9 Gy) for the ipsilateral lachrymal gland and 0.6 Gy (range: 0.3 – 0.6 Gy) for the contralateral eye. Treatment delivery was well tolerated. Plans were optimized down to a median of 42 beams, for planned delivery times of 8.8 to 15 minutes. The mean follow-up was 8 months. No patient has yet presented a clinically significant change in visual acuity. With this early follow-up, no patient has had a local progression. Two patients have suffered Grade 2 toxicities: one patient presented an exudative retinal detachment, in addition the patient treated for the recurrent disease presented ocular pain secondary to a neovascular glaucoma treated by topical medication and analgesics. Conclusion: While further follow-up is warranted, initial results indicate that hypofractionated Cyberknife stereotactic radiotherapy is technically feasible and well tolerated in the management of peri-papillary ocular melanoma.