New developments in external beam radiotherapy for retinoblastoma: from lens to normal tissue-sparing techniques

Historically, retinoblastoma was treated with external beam radiotherapy (EBR) and for many years this was the accepted standard of care. With greater knowledge of radiation-induced morbidity and mortality, the trend over the past decade has shifted towards primary chemotherapy for most globe conservative treatments. Such a radical change in treatment modalities has restrained EBR to second-line and salvage indications with little consensus regarding dose, timing and techniques. New radiotherapy options now allow for more focused radiation to the globe with further sparing of adjacent structures in such a way that their role in the management of retinoblastoma need to be reappraised. In this perspective paper, first the historical techniques of using EBR primarily with linear accelerated photons are reviewed. Then modern approaches are described, such as stereotactic conformal radiotherapy using a micromultileaf collimator, and proton therapy using a fixed horizontal beam and tantalum localization, or a rotating ganthry with spot scanning. For the first time, to the authors' knowledge, the benefits of these new irradiation modalities over conventional EBR are illustrated with six successfully treated pilot cases. Finally, some guidelines are provided regarding indications to modern radiation therapy in patients requiring second-line or salvage treatment for intraocular retinoblastoma, as well as adjuvant therapy for orbital involvement.