Modern radiosurgery equipment for treating brain metastases.

Radiosurgery plays an important role in the management of brain metastases, which are the most common indication for such treatment in many centers. Because brain metastases are well enhanced on magnetic resonance images and show clear margins from the surrounding normal brain, they are suitable for radiosurgery. The dedicated radiosurgery machines used for treating brain metastases have different characteristics from the conventional external beam radiotherapy machines, although the same gamma rays are used in both methods. In a radiosurgery procedure, highly concentrated radiation is given to a predefined target so that every cell inside it is affected. To achieve this, a radio-surgery machine should provide a highly accurate and precise delivery of radiation to the target with a steep dose gradient relative to surrounding tissues. Among the diverse dedicated machines that are in clinical use for radiosurgery of brain metastases, three - the Gamma Knife(®), CyberKnife(®), and Novalis(TM) - will be reviewed in this report. The basic principles of each machine for achieving a high convergence of radiation and for adjusting the radiation beam to conform to the target are described. The mechanical accuracy and characteristics of treatment plans are discussed briefly.