Abstract
We report three patients with cerebral arteriovenous malformations (AVMs) treated twice each by means of gamma knife radiosurgery: Case 1; 16 year old girl with an AVM located in the splenium of the corpus callosum, Case 2; 9 year old boy with a pontine AVM and case 3; 14 year old boy with an AVM located in the left middle temporal gyrus. In cases 1 and 2, three- or two-year angiography demonstrated small persistent residual nidi and sequential angiographic studies showed no nidus shrinkage over the two year period following these examinations. In case 3, however, three year angiographic examination disclosed a residual nidus which was located outside the previously irradiated region. At the time of reirradiation, in cases 1 and 3, more than 20Gy was delivered at the periphery because the target volumes were very small and the residual nidi were located in noncritical brain structures. In case 2, however, because of the nidus location (within the pons), we selected the same dose (16Gy) as that used in the initial treatment, although this dose was not considered to be optimal. Relatively little information is available on the doses used for reirradiation: What is the safest, optimal dose for achieving AVM obliteration? Further study of many such cases is necessary to resolve these issues.
Although follow-up angiography has not yet been performed in these patients, in cases 1 and 2, magnetic resonance (MR) angiography showed no vascular abnormalities and MR images suggested nidus obliteration 29 and 20 months, respectively, after reirradiation. The three patients have experienced neither rebleeding nor complications related to irradiation for, respectively, nine, six and six years since the initial gamma knife radiosurgery.
Based on these three cases, as well as our long-term follow-up experience with AVM patients treated by gamma knife radiosurgery, we have tentatively concluded that: 1) If the initial treatment was optimal, the patient should be followed without reirradiation as long as diminution of the nidus size is angiographically verified to be ongoing, regardless of the results of examination at three years. 2) If the initial treatment was less than optimal, the second course of gamma knife treatment should be done three years after the initial irradiation.
