A 42-year-old woman with recently diagnosed Graves' disease presents with bilateral eye protrusion (marked **A** in the diagram) and complaints of eye discomfort, tearing, and difficulty closing her eyes at night. She is a current smoker with 15 pack-years. Thyroid function tests show inadequately controlled hyperthyroidism despite antithyroid therapy. Which of the following is the MOST important modifiable intervention to prevent progression of her orbital disease?