Gamma knife radiosurgery for pituitary tumours.

Stereotactic radiosurgery with the gamma knife delivers focused radiation from a cobalt-60 source in a single session to a pituitary tumour with minimal radiation to the adjacent normal brain tissue. Currently, gamma knife radiosurgery is predominantly used to treat failed pituitary surgery, although it has a role as a primary treatment for patients unwilling or unsuitable, for medical reasons, to undergo trans-sphenoidal surgery. The major risk from gamma knife radiosurgery is radiation damage to the visual pathways, but this can be avoided by limiting the radiation dose to the optic chiasm to under 10 Gy. In contrast, the neuronal and vascular structures running in the cavernous sinus are much less radiosensitive, allowing an ablative dose to be administered to tumours showing lateral invasion and impinging on cranial nerves III, IV, V and VI. Gamma knife radiosurgery appears to produce remission in secretory tumours faster than fractionated radiotherapy. Furthermore, the potential long-term risk of developing a second extra-pituitary brain tumour, as well as the neuropsychiatric effects associated with conventional radiation administration, seems less likely to occur with this form of treatment.