The outcome of linear accelerator radiosurgery: is an early angiogram needed?

In this issue of the American Journal of Neuroradiology (page 475), Oppenheim et al document an extensive experience with linear accelerator radiosurgery for 197 patients over a 4-year period (January 1990 to December 1993). Of the 197 patients treated, 138 had what was defined as an ‘‘early’’ angiographic follow-up 6–18 months after treatment. The authors’ stated aim was to determine if an early angiogram was predictive of patients’ final outcomes. The radiosurgical treatment parameters the authors list in Table 2 are consistent with previously published reports of linear accelerator radiosurgery with a median peripheral prescription dose of 25 Gy for small arteriovenous malformations (AVMs): median target volume 2.67 cc; medium maximum dimension of 2.2 cm. Of note, 73 (53%) of 138 patients had single isocenter surgeries, treatments that cannot be highly conformal to target and isodose target outlines. Previous investigators have identified incomplete nidus coverage as one of the main reasons AVM obliteration can fail after radiosurgery (1). The authors’ overall obliteration rate (67.4%) is consistent with prior reports. The predictive value of an early angiogram was determined by whether or not complete obliteration occurred with intermediate or late angiographic follow-up. The findings indicate that a lower percentvolume reduction on the ‘‘early’’ angiogram corresponded to a lower rate of complete obliteration. Only 10% of those in the 0–25% volume reduction group went on to complete obliteration. In this sense, the ‘‘early’’ angiogram appears to have predictive value regarding later outcome, and I would agree with the authors that in the nonresponding patients with a prior history of hemorrhage, other treatment techniques should be discussed. In this article, as with others, the rehemorrhage rate of