Toward an expanded view of radiosurgery.

Radiosurgery and radiotherapy were originally distinguished on the basis of the manner in which they protected normal tissues from radiation injury. Radiosurgery does so by precise targeting of cross-fired radiation beams to abnormal tissue, with abrupt falloff of radiation doses to surrounding normal tissue. Radiotherapy was historically less concerned with targeting accuracy and anatomic precision; normal tissues were protected by dividing doses into multiple fractions separated by time to allow recovery of normal tissues. By this means, radiotherapy applied radiobiological principles to disrupt dividing cells selectively. Despite the development of computer-based, image-guided frameless technology that eliminates the necessity to perform radiosurgery in a single session, there are some who still insist that radiosurgery be distinguished from radiotherapy on the basis of whether treatment is delivered in a single session. Here, we propose that this definition of radiosurgery is needlessly restrictive and that staging or hypofractionation of radiosurgical treatment permits the limited application of radiobiological principles of radiotherapy to improve radiosurgical treatment. We therefore define radiosurgery as a procedure that involves the active participation of a surgeon and in which spatially accurate and highly conformal doses of radiation are targeted at well-defined structures with an ablative intent.