2899 - Image Guided IMRT for Thyroid Eye Disease: A Single-Center Study Using a Uniform 18 Gy Regimen
Presenter(s)
S. Tian1, and Q. Han2; 1Peking University 3rd Hospital, beijing, China, 2Peking University Third Hospital, Beijing, China
Purpose/Objective(s): Thyroid eye disease (TED) poses significant treatment challenges, especially in patients resistant or intolerant to corticosteroids. This study aimed to evaluate the efficacy, feasibility, and safety of image-guided intensity-modulated radiotherapy (IG-IMRT) using a uniform 18 Gy / 10 fraction regimen for TAO and to explore correlations between extraocular muscle (EOM) volumetric changes and functional outcomes.
Materials/Methods: Twenty-eight consecutive patients with moderate-to-severe active TAO unresponsive to corticosteroids were retrospectively reviewed at Peking University Third Hospital (2020.10–2025.03). Some patients had prior exposure to teprotumumab or mycophenolate mofetil (MMF). All patients received bilateral orbital IG-IMRT with 18 Gy in 10 fractions (1.8 Gy/fraction) over two weeks. Cone-beam CT (CBCT) verification was performed twice weekly for image guidance. Clinical assessments included changes in Clinical Activity Score (CAS), ocular motility (EOMy), diplopia (Gorman scale), and proptosis at baseline, 4, 6, and 12 months. MRI-based volumetric measurements of inferior and medial rectus muscles were performed using 3D Slicer software. Toxicities were graded per CTCAE v5.0.
Results:
The median follow-up period was 12 months. The Clinical Activity Score (CAS) significantly decreased from 5.6 ± 2.0 to 3.1 ± 2.3 at 12 months (p < 0.001). Both the radiotherapy-alone group and the radiotherapy plus corticosteroid group showed significant improvement (p < 0.01). Diplopia grade improved in 68.6% of eyes, and the amplitude of extraocular motility (EOMy) also increased markedly. MRI demonstrated an 11.2% ± 5.8% reduction in inferior rectus muscle volume and a 10.6% ± 6.3% reduction in medial rectus muscle volume, which correlated with functional improvement (r = 0.64, p < 0.01). Minor acute toxicities included periorbital edema, conjunctival hyperemia, and dry eye. No cases of radiation retinopathy, optic neuropathy, or cataract were observed.
Conclusion: Image-guided intensity-modulated radiotherapy using a uniform 18 Gy/10 fractionation protocol is a safe and effective treatment for hormone-resistant thyroid-associated ophthalmopathy, significantly and continuously improving inflammation and eye movement conditions. The volume reduction in magnetic resonance imaging is consistent with functional recovery, supporting its use as an early biomarker for treatment response.