Plaque Radiotherapy in the Management of Retinoblastoma: Use as a Primary and Secondary Treatment

Abstract

Radioactive episcleral plaque brachytherapy is a treatment method for selected retinoblastomas. The authors have used this technique since 1976 as both a primary and a secondary treatment method after other methods failed to achieve tumor control. A review of the records of 400 consecutive children with retinoblastoma showed that solitary plaque radiotherapy was used as a method of management in 103 cases. The authors' overall experience was evaluated, and the results between primary and secondary plaque therapies were compared in these 103 cases. Of the 103 tumors, the mean basal diameter was 7 mm, and the mean thickness was 4 mm. Overlying vitreous seeds were clinically apparent in 50 cases (48%). The mean proximity of the tumor margin to the optic disc margin was 6 mm and to the foveola was 6 mm. The mean follow-up period was 40 months. In 89 cases (86%), the tumor was controlled by one plaque application, whereas in 13 cases (13%), tumor recurrence after initial tumor shrinkage necessitated subsequent treatment. Final visual outcome was good in 63 cases (62%), poor in 30 (29%), enucleation in 9 (9%), and unknown in 1 case. The poor vision was due to foveal retinoblastoma (with or without amblyopia) in 25 cases (83%). Eight of the nine enucleated eyes were treated initially with external beam radiotherapy then later with plaque radiotherapy. In 31 cases (30%), plaque radiotherapy was used as a primary treatment to the tumor, while in 72 cases (70%), it was a secondary form of management after failure of other methods to control the tumor. Statistical analysis showed that tumors treated with plaque radiotherapy as a primary measure were more likely to be larger in in base (P = 0.01) and thickness (P = 0.01) than secondary treated tumors. The secondary treated retinoblastomas were more likely to have vitreous seeds (P = 0.02) than the primary treated tumors. The rate of tumor control and patient survival was similar between the two groups. Plaque radiotherapy is very effective in treating selected retinoblastomas with a high rate of tumor control and patient survival. It can be used successfully as a primary or a secondary treatment for tumors that have not been adequately controlled by other therapeutic methods.