Role of gamma knife radiosurgery in acromegaly.

Stereotactic radiosurgery with the Gamma Knife allows the delivery of focused radiation in a single session from a Cobalt-60 source to a pituitary tumor with little radiation to surrounding normal brain tissue. At this time the major role for Gamma Knife radiosurgery in acromegaly is for the treatment of failed pituitary surgery although it may also by used as primary treatment for patients unwilling or unsuitable, for medical reasons, to undergo transsphenoidal surgery. The major risk from Gamma Knife radiosurgery appears to be radiation damage to the visual pathways, but this can be obviated by limiting the radiation dose to the optic chiasm 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 tumors showing lateral invasion and impinging on cranial nerves III, IV, V and VI. Gamma Knife radiosurgery appears to produce effects in GH secreting tumors faster than with fractionated radiotherapy without the potential long-term risk of developing a second extrapituitary brain tumor as well as the neuropsychiatric effects associated with conventional radiation administration.