Cushing's Syndrome – Radiotherapy Radiotherapy as a definitive therapy may be given conventionally using a linear accelerator or a cobalt source. Conventional external pituitary radiotherapy takes 2–10 years to achieve a cure, except in children who appear particularly sensitive to this form of treatment. This method of treatment is used in combination with medical therapy to control cortisol secretion unless the patient has had an adrenalectomy. Radiotherapy is now largely limited to patients in whom transsphenoidal hypophysectomy has been partially or completely unsuccessful, or if a total adrenalectomy has been performed.