Levothyroxine is typically used after which types of medical treatment?

Levothyroxine is a synthetic form of the thyroid hormone thyroxine (T4) and is commonly prescribed to treat hypothyroidism, a condition where the thyroid produces insufficient hormones. This medication is often used after surgical interventions aimed at the thyroid, particularly in cases where there has been a partial or total thyroidectomy.

When a patient undergoes surgery, such as the removal of the thyroid gland or parts of it, the body's ability to produce thyroid hormones can be severely impacted. As a result, Levothyroxine is administered to help restore normal hormone levels and maintain proper metabolic function. Additionally, radioactive iodine therapy is another treatment for hyperthyroidism or thyroid cancer that can lead to a deficiency in thyroid hormone production. Following this treatment, patients may also require Levothyroxine to manage their hypothyroid state.

In the context of the other choices, while chemotherapy and radiotherapy can have various side effects, they do not directly relate to the need for Levothyroxine. Similarly, cardiac surgery and insulin therapy do not create a specific requirement for thyroid hormone replacement. Thus, the combination of surgery and radioactive iodine therapy is specifically linked to Levothyroxine use, confirming why this option is the correct choice.