Radiation therapy for orbital tumors: concepts, current use, and ophthalmic radiation side effects

Radiation therapy is widely used for the treatment of orbital tumors and inflammatory disease. Both external beam teletherapy and implant brachytherapy radiation techniques are employed. External beam radiation therapy is the most common. It involves directing an external radiation source towards the eye, sinuses, and orbit. Whereas most patients are treated with linear accelerator-derived external beam radiation therapy, proton, neutron stereotactic radiosurgery, gamma knife, and intensity-modulated radiation therapy have become more available in developed countries. Radiation can be used alone or together with surgery or chemotherapy. Implant radiation therapy (brachytherapy) is also used to treat orbital tumors. Brachytherapy involves surgical placement of radiation sources within the tumor or targeted volume. Characteristically conformal, brachytherapy increases the dose within the target while maximally decreasing exposure of normal tissues. Orbital brachytherapy can be used to boost the dose to the target volume prior to orbital external beam radiation therapy. Herein, I explore the unique challenges associated with irradiation of the orbit, basic radiobiology, doses, indications, and results of treatment. The tolerances of normal ocular and orbital tissues are reported. This review of the literature offers a unique perspective, synthesizing the world's experience on the use of orbital radiation therapy.