Quantitative analysis of extraocular muscle volume and exophthalmos reduction after radiation therapy to treat Graves' ophthalmopathy: A pilot study

Abstract

Purpose: The aim of this study was to provide radiological information on the inherent response of Graves' ophthalmopathy after radiation therapy. Methods: Quantitative analysis of extraocular muscle volume was performed on 96 involved extraocular muscles in a total of 16 patients. A total of 48 computed tomography images were analyzed. Exophthalmos was also measured. The percentage reductions in extraocular muscle volume and exophthalmos length were determined and compared to the pre-radiation therapy values at 6-, 12-, and 24-month follow-up. Results: The median follow-up time was 21.5 months (range: 7.2-29.4 months). The mean reduction in relative tumor volume compared to the pre-radiation therapy extraocular muscle volume was 46.1% (range: 33.3%-58.8%). The mean relative extraocular muscle volumes were 71.5% at 6 months, 59.2% at 12 months, and 54.3% at 24 months after radiation therapy. The volume of the involved extraocular muscles decreased rapidly within the first 12 months of follow-up. The mean pre-radiation therapy length of exophthalmos was 21.7 mm (range: 17.6-26.1 mm). The mean percentages of exophthalmos length by comparison with the pre-radiation therapy length were 96.7% at 6 months, 92.3% at 12 months, and 88.5% at 24 months after radiation therapy. Exophthalmos decreased slowly and steadily during the follow-up period. Conclusion: Quantitative volumetric analysis of the pattern of extraocular muscle volume reduction and exophthalmos length reduction in response to radiation therapy will allow clinicians to better understand the effect of radiotherapy on Graves' ophthalmopathy.