Radiosurgery using a modified linear accelerator.

Stereotactic radiosurgery using modified LINACs is a powerful new technique that offers a versatile method for administering high-dose radiation in a single session. Treatment-planning techniques currently in use enable individual isocenter field shaping, three-dimensional optimization of isocenter placement (including the use of multiple isocenters), and real-time analysis of isodose distribution in three dimensions relative to specifically defined anatomic structures from MR imaging or CT data. Modified linear accelerators offer successful control of both arteriovenous malformations and benign tumors (acoustic neuromas, craniopharyngiomas, and meningiomas), with results equal to the best series reported by users of the gamma knife or heavy-particle systems. More recent work indicates that radiosurgery may play an important role in controlling recurrent pediatric malignant tumors, metastatic cerebral lesions, and even malignant astrocytomas in some patients. Improved correlation of isodose distributions with imaging data allows for sophisticated analysis of results and specific complications, ultimately enabling improved patient care using this exciting new technique.