Radiation Therapy in the Management of Retinoblastoma

Abstract

Radiation therapy is a primary treatment for retinoblastoma resulting in high rates of disease control and functional organ preservation. Late effects from treatment, including secondary tumor formation in patients with genetic predisposition have, during the past 15 years, led investigators to pursue treatment approaches that delay or omit radiation therapy. Currently, the role of radiation therapy in the management of retinoblastoma remains in a state of uncertainty, and the number of patients irradiated using external beam methods is on the decline even as cure rates continue to increase (Broaddus et al. 2009). Investigators and caregivers await firm evidence that visual outcomes and eye preservation are equivalent with newer approaches that include episcleral plaque brachytherapy as a component of local therapy in the current front-line management for selected patients (Antoneli et al. 2006).

In the treatment of retinoblastoma, radiation therapy provides the benchmark for the evaluation of tumor control, for eye preservation, and for side effects. Its role has been diminished by its known contribution to secondary tumors in a high-risk population and the move toward chemotherapy combined with local ophthalmic therapy (Wilson et al. 2001). Radiation therapy is the most effective nonsurgical treatment for retinoblastoma. It is the only treatment for which long-term data identify attribution of late effects in vulnerable young patients and those with genetic susceptibility to malignancy induction. Radiation therapy has an excellent track record in preservation of the eye. In patients with Reese-Ellsworth group I-II disease, tumor control rates measured at 5 years are in excess of 95%. In patients with more advanced disease (Reese-Ellsworth groups III and IV), 5-year control rates reduce to approximately 50%, partly owing to the greater tumor burden and intraocular extent of disease (Blach et al. 1996). Patients with Reese-Ellsworth group VB disease have 5-year eye-preservation rates of approximately 53% (Abramson et al. 2004a). Poor tumor control in advanced cases is often attributed to vitreous seeding. Although data on visual acuity are relatively limited, most patients are reported to have good visual acuity (20/20-20/40) after radiation therapy; the rest have at least some prospect for functional vision (20/50-20/400) (Egbert et al. 1978; Hall et al. 1999). Visual acuity and field after therapy are affected by tumor location, tumor size, and treatment (Abramson et al. 2004b), which often depend on the patient’s age at the time of diagnosis; younger patients are more likely to have tumors about the macula (Brinkert et al. 1998).