Movement disorder radiosurgery--planning, physics and complication avoidance.

Gamma Knife radiosurgical thalamotomy is an effective and useful alternative to invasive radiofrequency techniques for patients at high surgical risk. The mechanical accuracy of the gamma unit combined with the anatomical accuracy of high-resolution MRI make radiosurgical lesioning safe and precise. Higher radiosurgical doses are more effective than lower ones at eliminating or reducing tremor, and are generally without complications. The results from radiosurgical pallidotomy, as opposed to those of gamma thalamotomy, have been disappointing. A 50% complication rate in the former (homonymous field cuts, hemipareses and dysphagias) combined with a poor success rate has led us to reevaluate the indications for this procedure in the face of the excellent results from radiofrequency pallidotomy with physiological monitoring and deep brain stimulation. Perhaps experience with lowered radiosurgical prescription doses will improve the complication rate. There appears to be a differential sensitivity of the pallidum to radiation, anatomically, than the thalamus. Age-related or anatomy-related susceptible blood supply to the area may lead to hypoxia after singlefraction radiosurgery, in a nuclear complex known to be especially susceptible to hypoxia. In addition, varying levels of iron deposition within the pallidum may catalyze free radical formation in the elderly only to be further exacerbated by tissue hypoxia. Although reported, the success of radiosurgical caudatotomy, subthalamotomy and lesioning of the VL nucleus remains to be further elucidated.