RESUMO
Stereotactic radiotherapy is a form of external radiotherapy that employs a system of three dimensional coordinates independent of the patient for the precise localisation of the lesion. It also has the characteristic that the radiation beams are conformed and precise, and converge on the lesion, making it possible to administer very high doses of radiotherapy without increasing the radiation to healthy adjacent organs or structures. When the procedure is carried out in one treatment session it is termed radiosurgery, and when administered over several sessions it is termed stereotactic radiotherapy. Special systems of fixing or immobilising the patient (guides or stereotactic frames) are required together with radiotherapy devices capable of generating conformed beams (lineal accelerator, gammaknife, cyberknife, tomotherapy, cyclotrons). Modern stereotactic radiotherapy employs intra-tumoural radio-opaque frames or CAT image systems included in the irradiation device, which make possible a precise localisation of mobile lesions in each treatment session. Besides, technological advances make it possible to coordinate the lesion's movements in breathing with the radiotherapy unit (gating and tracking) for maximum tightening of margins and excluding a greater volume of healthy tissue. Radiosurgery is mainly indicated in benign or malign cerebral lesions less than 3-4 centimetres (arteriovenous malformations, neurinomas, meningiomas, cerebral metastases) and stereotactic radiotherapy is basically administered in tumours of extracraneal localisation that require high conforming and precision, such as inoperable early lung cancer and hepatic metastasis.
