**3. Tumor control and biochemical control**

For skull base meningiomas, nonfunctioning pituitary adenomas, craniopharyngiomas, and vestibular schwannomas, the major goal of treatment is tumor control. Tumor control is defined as stable or reduced size of tumor after treatment. Long-term tumor control after fractionated stereotactic radiation therapy of benign anterior skull base tumors is well established from several large series and in several cases is superior to surgery, with long-term tumor control rates reported in the range of 88–100% for skull base meningiomas [4, 24, 41–46], 92–99% for pituitary adenomas [47–53], 75–100% for craniopharyngiomas [34, 37, 54, 55], and 85–100% for vestibular schwannomas [38, 40]. Long-term tumor control rates after stereotactic radiosurgery with LINAC or Gamma Knife have been reported to be similar [2, 4, 6, 8, 9, 36, 38, 56]. For hormone-secreting pituitary adenomas, an equally important goal of treatment is biochemical control [56]. For nonfunctioning pituitary adenomas, biochemical control rates of 50% of hormone-producing adenomas have been reported [7].

Tumor control can be evaluated on a contrast-enhanced MRI scan compared with the MRI scan before the radiation therapy. Pre- and post-therapy MRI and CT scans of the treatment plans are fused, with the gross tumor volume as reference [57]. Tumor volume is then calculated using 3D volumetric assessment with treatment planning software, i.e., from Electa, BrainLab, or Varian Eclipse. Tumor control is defined as stable size or regression of the tumor. A change in tumor volume by ≥25% can be considered a change in size, and a change in tumor volume < 25% can be considered stable size [34].

Serial neuroimaging follow-up until at least 10 years after treatment is generally recommended.
