Radiation therapy for benign disease of the orbit

Abstract

Benign diseases of the orbit can cause significant impairment of visual function through direct effects on the eye or supporting orbital tissues. Persistent moderate-to-severe inflammatory symptoms, diplopia, and visual loss may prompt therapeutic intervention. Low doses of external-beam irradiation (20 Gy in 2-Gy fractions) have an efficacy equivalent to corticosteroid medications in the treatment of both Graves' ophthalmopathy and orbital pseudotumor, with response rates of 50% to 80%. Appropriate patient selection, coordination with other medical subspecialties, and careful treatment planning are important in maximizing benefit from radiation therapy. In the case of Graves' ophthalmopathy, quantitative assessment of orbital disease severity and thyroid status as well as attainment of cross-sectional imaging should be performed before treatment. Patients whose thyroid disease is controlled but who have moderate-to-severe active orbital involvement can be offered orbital radiation therapy with a high likelihood of response. Stability of disease is generally obtained within 6 months; surgical correction of residual abnormalities may be required. For orbital pseudotumor, attainment of histological material before treatment is important in excluding benign or malignant systemic diseases, including malignant lymphoma. Genotypic abnormalities may exist in patients with reactive lymphoid hyperplasia, some of whom ultimately develop systemic lymphoma. Within the dose range recommended for treatment of Graves' ophthalmopathy and pseudotumor, late radiation effects on the retina or optic nerve should be nonexistent. Adequate lens shielding is required, however, to prevent cataract formation. This may require individualized treatment planning with computed tomography at the time of simulation. Pterygia recurrence after bare sclera excision occurs in at least 30% of cases, usually within 6 months of surgery. Radiation of the surgical bed using a strontium-90 source, beginning within 24 hours postoperatively, reduces the risk of recurrence substantially. Late scleral complications have been associated with large single-fraction treatments. To achieve maximal efficacy with minimal complications, fractionated treatment should be given by radiation oncologists experienced with the technique using sources calibrated by the National Bureau of Standards.