Is There a Role for Fractionated Radiotherapy in the Treatment of Arteriovenous Malformations?

Single fraction radiotherapy for the treatment of arteriovenous malformations (AVMs) is appropriate when brain tolerance is not a limiting factor, but when tolerance is a concern, there is a potential for therapeutic gain with fractionated treatment. alpha/beta values for AVM obliteration have been derived and found to be higher than previously assumed and are likely to be approximately 10.0 Gy or more compared with approximately 1.5 Gy for the tolerance of small volumes of brain. Models are derived to describe, qualitatively, the potential gain that can be achieved with fractionation. Past experience has identified an important volume effect that has limited the use of stereotactic treatments to small volumes. Volume-dependent, dose-volume relationships are described, including a tissue-specific volume exponent (phi) which was found to apply across a relatively wide range of target volumes, thereby permitting the derivation of tolerance guidelines to volumes larger than previously available. More data to define parameter values more precisely are desirable.