Typical MRI scan changes in GH adenoma. Coronal T1-weighted postcontrast MRI scan at upper left and right, obtained in Patient 3, a 33-year-old man who presented with GH adenomas and acromegaly 7 years before undergoing MASEP GKRS. (Figure 5) An enhancing mass lesion is seen in the sella turcia with extension into the left cavernous sinus. Patient 3's serum growth hormone level was 497.3 ng/ml initially. He was treated with transsphenoidal surgery, and the tumor relapsed shortly with the serum growth hormone level reduced to 130.2 ng/ml. The patient was treated with MASEP GKRS, and MRI was performed for treatment planning. 20 Gy defined to the 50% isodose line is used to cover the full extent of the pituitary tumor in the first radiosurgery, and 28 Gy defined to the 50% isodose line is used to cover the pituitary tumor in the second time one year later.