A patient treated with Gamma Knife radiosurgery is considered to be in remission if the excessive hormone secretion becomes normal. In the case of patients with acromegaly, the definition of remission is a normal age- and gender-adjusted serum IGF-1 concentration. IGF-1 is the best indicator of overall GH secretion. Because GH production is influenced by age and gender (GH secretion declines with increasing age), it is necessary to have the IGF-1 level measured in a laboratory that provides normal values in relation to age and gender. In patients with CD, the 24-h UFC concentration is the best measure of integrated cortisol production. A normal 24-h UFC is an excellent measure of excessive cortisol production but is not helpful to assess adrenal insufficiency. A single serum PRL measurement in a patient with a prolactinoma is sufficient to assess the response to Gamma Knife therapy. Gonadal function is assessed by a history of normal libido and erectile function and a normal serum testosterone in men. In premenopausal women, regular menses indicate normal ovarian function. Men should have serum testosterone measured regularly, and menstrual history and serum estradiol levels should be measured in premenopausal women. In patients with Nelson's syndrome (increased serum ACTH after bilateral adrenalectomy), measurement of the serum ACTH level indicates the response to Gamma Knife treatment. Regular magnetic resonance imaging (MRI) examinations, usually once a year, are necessary to assess the effect of treatment on tumor volume. Both endocrine and imaging studies are necessary to properly evaluate the response to treatment and should be considered complementary. In the situation of patients with a secretory tumor, however, the definitive assessment of the response to treatment resides in the hormone measurements.
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