it is occasionally used in the patient with more than three lesions, it is usually reserved for patients with single or, at most, several metastases. Median duration of patient survival following radiosurgery for an intracranial metastasis is 7-12 months, similar to that for surgical resection [11]. Randomized studies comparing radiosurgical and surgical treatments for single brain metastases have not yet been completed.

Whether WBRT is needed in addition to radiosurgery for single metastases is controversial. Much of the radiosurgical data was accumulated in patients who also received WBRT and, given the conformal nature of the radio-surgical treatment volume, it is unlikely that the addition of WBRT to radiosurgery significantly increases the risk of radiosurgery. Nonetheless, given the inefficacy and toxicity of WBRT and the ability to detect and to treat new lesions con-formally with radiosurgery, radiosurgery alone may be appropriate initial treatment for most metastases of appropriate size. Essentially, stereotactic radiosurgery and WBRT can be viewed as complementary: radiosurgery focally targets one to three tumors of 1-10 cm3 in volume, whereas WBRT intends to control higher numbers of small tumors or microscopic spread throughout the brain. Radiosurgery alone is most strongly indicated for a single metastasis from systemic tumor that is indolent or well controlled (and thus not an immediate threat to survival) and of a histologic type prone to single brain metastases (e.g. breast and non-small cell lung carcinoma) or relatively refractory to fractionated radiotherapy (e.g. melanoma, renal cell carcinoma and sarcoma). WBRT is likely needed in addition to radio-surgery when there are multiple cerebral tumors, especially those with histologies prone to disseminated brain metastases and high sensitivity to fractionated radiation (e.g. small cell lung carcinoma, testicular carcinoma and lymphoma). In many patients with these histologies, WBRT is given first and radiosurgery is reserved for tumors that subsequently resume growth. When brain metastases are multiple and systemic disease is refractory to treatment, WBRT alone is given as palliation.

Interstitial brachytherapy (the temporary or permanent placement of radioactive seeds within a tumor) and interstitial radiosurgery (the transient stereotactic placement of the tip of a miniature generator of X-rays within a tumor) also achieve high-dose focal irradiation of brain metastases. Their invasiveness, with the concomitant risks of infection and hemorrhage, and their limited conformity are disadvantages relative to radiosurgery. However, they do offer an additional treatment option for single, surgically inaccessible tumors that are too large to be treated safely and effectively with radiosurgery.

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