Extracranial stereotactic radiosurgery: Applications for the spine and beyond

The concept of extracranial stereotactic radiosurgery elegantly connects the origins of the stereotactic method and the future of surgical praxis. In its cranial application, stereotactic radiosurgery has proved itself clinically useful and economically advantageous. Spinal extracranial applications are still in the experimental phase. The number of patients treated with the Hamilton-Lulu frame is under 25, and only 2 patients have been treated with the Cyberknife. Their life expectancies have been short due to disseminated metastatic disease, but they have shown that the concept is clinically feasible. Local tumor control was achieved in a majority of cases, and no patient's condition worsened due to the treatment. Importantly, radiation myelitis was not seen during the available follow-up period. The Swedish clinical series of 50 patients with abdominal and thoracic tumors clearly shows the efficacy of the concept and that it is possible to achieve a high degree of accuracy with fractionated therapy in a noninvasive frame. For the central nervous system, intra- or extracranially, LINAC or GKU, the maximum degree of accuracy required necessitates either a bone screw fixation frame or a currently expensive frameless system. As patient selection has been limited to individuals with end-stage disease, the treatments have been purely palliative, and follow-up has been limited in time. More studies are needed to ensure that no long-term damage is caused to the spinal cord. The frame concept needs further refinement. Based on the data available, extracranial stereotactic radiosurgery may be as potent and cost-effective as intracranial stereotactic radiosurgery.