Background: Graves' disease (GD) is an autoimmune disease that typically affects the thyroid gland. Thirty to sixty percent of patients also suffer from orbital inflammation. Retrobulbar radiotherapy for Graves' orbitopathy (GO) has been used for decades, though there is no direct evidence for the influence of dose and fractionation schedules on various signs and symptoms. Indeed, optimal fractionation schedules and recommended total irradiation doses are still a matter of discussion. Our aim was to investigate treatment efficacy of retrobulbar irradiation for GO at different total absorbed doses and fractionation schedules.
Methods: A retrospective evaluation of 129 patients who were examined before, as well as 6-8 months after irradiation with different treatment schedules at eight radiotherapeutic departments. Total absorbed doses were 12, 16, or 20 Gy. All patients were additionally treated with systemic application of corticosteroids. Treatment efficacy was evaluated through assessment of proptosis, horizontal and vertical ocular motility and of clinical activity (CAS). Overall group and individual responses were evaluated. Treatment response was defined as inactivation of GO, reduction of proptosis by at least 2 mm, improvement of motility by > or = 8 degrees or unchanged normal parameters.
Results: Prior to irradiation, neither age, disease duration, gender distribution, smoking behavior or serologic parameters, nor clinical activity or severity stages varied significantly between groups. Neither did outcome measures, except proptosis, differ significantly. Retrobulbar irradiation led to inactivity of GO in approximately 80% of patients, with no significant group difference. After irradiation with 16 and 20 Gy, vertical motility improved in a significantly higher percentage of patients than after irradiation with 12 Gy. Median improvement of vertical motility in responding patients was excellent in all groups (15 degrees at 12 Gy, 10 degrees at 16 Gy, 10 degrees at 20 Gy). Horizontal motility did not change significantly.
Conclusion: If the aim of retrobulbar irradiation is primarily to reduce soft-tissue signs, lower doses are sufficient. If a patient also suffers from dysmotility, doses exceeding 12 Gy may be more effective.