How effective is radiation therapy for NFAs?
External beam radiation therapy is excellent for controlling NFA growth; > 90% progression-free survival rates have been reported at 10 years in most series. Tumor control occurs regardless of the radiation technique or NFA subtype. Two general radiation modalities are used for pituitary adenomas: (1) conventional/conformal radiation, which is delivered in daily small fractions (1.8–2.0 Gy/day) over 5 to 6 weeks (45–54 Gy total); or (2) stereotactic radiosurgery (SRS), which is high-dose focused radiation, delivered as photons (e.g., Gamma knife, Cyberknife, LINAC) or protons (proton beam radiation). SRS treatment typically occurs as a single treatment or during a few (2–5) sessions (fractionated stereotactic radiotherapy), with a lower total radiation dose (15–20 Gy), but relatively high tumor dose. When feasible, SRS is generally preferred over conventional radiation because of its comparable treatment efficacy, patient convenience and possible lower rates of hypopituitarism. The choice of radiation is ultimately based on the tumor size and its proximity to the optic chiasm. Specifically, only smaller pituitary adenomas (< 3 cm) that are at least 5 mm from the optic chiasm (because of nerve toxicity at > 8 Gy doses) are considered for SRS. Lastly, small residual tumors may be monitored and not treated unless significant growth occurs.