Retrobulbar Irradiation for Graves’ Orbitopathy: A Retrospective Evaluation of Total Absorbed Doses of 12, 16 and 20Gy.

Aim:
To investigate treatment efficacy of retrobulbar irradiation for Graves? ophthalmopathy (GO) at different dose and fractionation schedules.
Methods:
129 patients were examined prior to, as well as 6-8 months following irradiation with different treatment schedules at eight radiotherapy departments. Total absorbed doses were 12 Gy, 16 Gy or 20 Gy. 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 more than 1.5 mm, improvement of motility by ? 5° or unchanged normal parameters.
Results: Prior to irradiation, neither age, disease duration, gender distribution, smoking behaviour 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° at 12 Gy, 10° at 16 Gy, 10° 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 around 16 Gy should be preferred.