Prognostic Factors for Eye Globe Salvage by External Beam Radiation Therapy for Resistant Intraocular Retinoblastoma

PURPOSE: To analyse the prognostic factors for eye salvage for eyes with intra-ocular retinoblastoma (RB) that is resistant to systemic chemotherapy and focal therapy by external beam radiation therapy (EBRT). METHODS: A retrospective analysis of 28 eyes with intra-ocular RB that was resistant for systemic chemotherapy and focal consolidation therapy and received EBRT. Outcome measures included tumor stage at diagnosis, stage migration, type of tumor seeds, treatment modalities, eye globe salvage, metastasis, and survival. RESULTS: Most of the patients (83%) had bilateral RB, and 42% were females. All eyes were treated initially by combination of systemic chemotherapy and focal consolidation therapy. The dose of EBRT was 45 Gy. The mean follow-up was 6.5 years, and the overall eye globe salvage rate post EBRT was 46%: 67% (2/3) for group B, 71% (5/7) for group C, and 33% (6/18) for group D. Patient's gender, tumor site, laterality, and tumor stage at diagnosis were not significant prognostic factors (p> 0.05) for final outcome. The significant poor prognostic factors were tumor stage migration during systemic chemotherapy (p= 0.03) and presence of vitreous seeds at time of EBRT (p=0.001). Post EBRT complication rate was 68% (19/28) including; retinal detachment (3), vitreous hemorrhage (4), neovascular glaucoma (1), cataract (16), radiation retinopathy (2), and second malignancy (2). CONCLUSION: EBRT is an alternative for enucleation when RB is resistant to combined chemoreduction/focal consolidation therapy in absence in vitreous seeds. The known risks for EBRT are not justified for patients with unilateral RB and for those who have functional vision in the other eye.