The main indications for the use of radiotherapy for the pituitary gland are for the treatment of secretory macroadenomas and for non-functioning tumours. The success rate for the surgical cure of these tumours is relatively poor, especially with suprasellar extension. Treatment with radiotherapy often inhibits further tumour growth.
This type of radiotherapy is generally delivered in fractionated doses of 1.6 - 1.8 Gy four to five times per week for five to six weeks. The response to this type of radiotherapy has been shown to be slow and incomplete. This type of therapy has also been associated with a high number of side effects such as hypopituitarism, secondary tumours and damage to the optic pathways.
The limitation in conventional radiotherapy for the treatment of pituitary tumours has resulted in alternative techniques for irradiating the pituitary. Stereotactic radiosurgery delivers radiation in a single session with high precission. This means that a high dose of radiotherapy is administered to the tumour itself with little radiation to surrounding tissue. There are three forms of radiosurgery available:
1) Gamma Knife Radiosurgery - this technique uses a cobalt-60 gamma radiation-emitting source focussed on the tumour. 2) Linear Acceleration (LINAC) - this technique also uses photons focussed on the tumour, but involves a moving gantry. 3) Proton Beam Therapy - this uses protons that release radiation energy when they stop rather when travelling through tissue.