Abstract
There have been numerous case reports and series of patients treated with partial brain irradiation, linear accelerator-based radiosurgery, gamma knife radiosurgery, and Bragg peak therapy for inoperable arteriovenous malformations (AVMs). These cases are summarized and compared. There is convincing evidence that radiation therapy does have a role in obliterating carefully chosen inoperable lesions. The changes that occur in vessel walls after radiation are reviewed. Data about x-ray and gamma radiation are mostly historical and difficult to evaluate because of the techniques of partial brain irradiation. There is a lack of data about the volume of AVM treated and the minimum dose delivered to the AVM nidus. For gamma knife, heavy particle, and linear accelerator therapy, more complete data are available. The incidence of hemorrhage during the first 2 years after treatment, when radiation-induced vascular changes are proposed to occur, is approximately 2.6% per year for gamma knife therapy, 2% per year for proton beam therapy, 2.3% per year for helium beam therapy, and 2.3% per year for linear accelerator therapy. These rates are similar to the recurrence rate for hemorrhage of 2.2 to 3% per year expected based on the natural history of untreated AVMs. If AVM obliteration after therapy is not achieved, the incidence of recurrent hemorrhage remains between 2% per year after treatment with gamma knife therapy. The incidence of hemorrhage for all patients treated was reported as 0.15% per year in one study and 20% over 8 years in a follow-up study using proton beam therapy. Mortality from hemorrhage after treatment was 0.6% after gamma knife therapy, 2.3% after helium beam therapy, and 2 to 5% after proton beam therapy. These figures for mortality are all lower than the 11% observed for the natural history of untreated AVMs. Permanent neurological deficits experienced as a complication of radiation occurred in 2 to 3% of patients treated with gamma knife therapy, 4% of patients treated with helium beam therapy, 1.7% of patients treated with proton beam therapy, and 3% of patients treated with stereotactic linear accelerator therapy. Proton beam therapy has been used for both small and large lesions. The majority of lesions in patients treated with gamma knife, helium beam, and linear accelerator therapy have been small (usually less than 3.0 cm average diameter) lesions. In these patients with small inoperable lesions treated with accurately directed fields of isocentric radiation, the greatest incidence of AVM obliteration has been observed on follow-up angiograms. Larger lesions may undergo vascular wall thickening with subsequent protection from recurrent hemorrhage, but more data are needed to support this hypothesis.
