The paper analyzes the effectiveness of external beam radiation therapy of medullary thyroid cancer in 38 patients. The radiation therapy of the first phase combined therapy was performed in 9 (24 %) patients: after treatment, 5 patients had a partial response, 4--stabilization. The radiation therapy of the second phase combined therapy was performed in 27 (71%) patients: after treatment, 2 patients had a complete response (booster method), 5--partial response, 4--stabilization. External beam therapy has been performed in 2 (5 %) patients with palliative and symptomatic goals. Additionally has been estimated level of calcitonin in patients after combined treatment. The calcitonin level becomes normal without radiation therapy. Therefore, exposure for medullary thyroid carcinoma is questionable (exception for cases gain exposure to the rest of the tumor).