Focal fractionated radiotherapy for intramedullary spinal arteriovenous malformations: 10-year experience

Object. Radiosurgical treatment of spinal arteriovenous malformations (AVMs) is becoming a practical therapeutic option as methodology improves, but no comparative study has yet been published on focal fractionated radiotherapy. The authors report their experience with conventional and hypofractionated radiotherapy for spinal AVM. Methods. Candidates for this study were patients who experienced symptoms due to an intramedullary AVM but were ineligible for embolization or surgery. Of 21 patients with spinal AVMs, 10 cases in a 10-year period met this criterion. Angiography and contrast-enhanced computerized tomography scanning were used for treatment planning in all cases. Fractionated radiotherapy was performed using a linear accelerator, extracranial immobilization system, and frequent orthogonal linacographic verification. The starting radiation dose was 32 Gy in two, 36 Gy in three, and 40 Gy in two patients, in a regimen involving 1.8 to 2-Gy daily fractions; this was recently changed to a hypofractionation schedule of 30 Gy (in eight sessions) in one and 20 Gy (in four sessions) in two patients. Results. The follow-up period ranged from 26 to 124 months (median of 49 months). There were no hemorrhages nor any adverse reactions attributable to irradiation. Of the seven patients who consented to undergo follow-up angiography, the nidus size decreased in five, but complete obliteration did not occur in any patient. Conclusions. Because no patient experienced adverse effects, the maximum tolerable radiation dose for the spinal cord associated with an AVM could not be identified, although it presumably is higher than those administered. The lack of rebleeding in patients in whom complete angiographic occlusion was absent suggests that the natural history of spinal AVMs may be less aggressive than previously reported.