I-125 Episcleral Plaque Brachytherapy for Uveal Melanoma: A 15-year Single Institution Experience

Abstract

To determine the long-term outcomes of I-125 episcleral plaque brachytherapy for uveal melanoma and identify dosimetric factors associated with ocular complications and tumor control. Medical records were reviewed for 494 patients treated with I-125 plaque brachytherapy for uveal melanoma from 1996 to 2011. Brachytherapy records for 436 patients were reviewed to analyze radiation doses at specific dose reference points. Ophthalmologic follow-up records were analyzed to assess the incidence of recurrence and ocular complications after therapy. Survival curves were estimated using the Kaplan-Meier method. Student's t test and Fisher's exact test were used to analyze the relationships of dose delivered and type of plaque to outcomes. Mean tumor thickness and long basal diameter were 4.9 mm and 12.1 mm, respectively. The median plaque size was 18 mm. One hundred ten plaques (22.6%) required a notch due to proximity to the optic nerve. The median follow-up was 42 months (range, 6-175 months). The estimated 5-year overall and cause-specific survivals were 73.2% and 88.6%, respectively. Local control was 95.3% with 26 local failures, and 56 patients (11.3%) developed metastatic disease. The mean doses to the tumor apex, tumor base, and prescription point were 98.8 Gy, 269.4 Gy and 85.6 Gy, respectively. The mean dose to the tumor base was similar in those with local control compared to those with local failures (269.1 Gy vs. 261.7 Gy; p = 0.74). The corresponding radiation dose to the tumor apex was 99.1 Gy versus 94.2 Gy (p = 0.15). Thirty-eight patients (6.8%) underwent enucleation. The reasons for enucleation included local recurrence (20 patients), second primary tumor (1 patient) and severe radiation toxicity (17 patients; 3% of treated patients). The mean dose to the tumor base in patients requiring enucleation was significantly greater than in those without enucleation (323.3 Gy vs. 263.5 Gy, p = 0.02). The corresponding mean radiation dose to the tumor apex was 95.1 Gy and 99.2 Gy (p = 0.11). Patients who required enucleation secondary to radiation toxicity had a significantly greater dose to the tumor base than those without enucleation (392.1 Gy vs. 263.7 Gy, p = 0.001). The corresponding mean radiation doses to the tumor apex were 92.3 Gy and 99.2 Gy (p = 0.07). There was no significant association between presence of a notch or size of the plaque and recurrence or enucleation (all p > 0.05). I-125 episcleral plaque brachytherapy leads to excellent local control and globe preservation. There is no association between need for a notched plaque or plaque size with tumor recurrence or need for enucleation. Patients requiring enucleation had higher a radiation dose to the base of the tumor.