Micromultileaf collimator-based stereotactic radiosurgery for selected arteriovenous malformations: Technique and preliminary experience

Purpose : To report our experience of stereotactic radiosurgery (SRS) in consecutively treated patients with arteriovenous malformations (AVMs).
Materials and Methods : Of the 87 patients, 23 patients qualified and were treated with SRS as per predefined protocol according to AVM size, location, neurological status, prior bleeding, and the AVM score. All had Spletzer-Martin grade II/III and AVM scores < 2.5. Patients underwent SRS using micromultileaf collimators delivering multiple noncoplanar fixed fields. Doses were prescribed using the Flickinger model. Patients were followed up with magnetic resonance angiography (MRA) and digitally subtracted angiography (DSA).
Results : The mean nidus volume was 3.65 cc. The mean prescribed maximum dose was 22 Gy and the marginal dose was 19.24 Gy; 12 Gy normal brain volume was 8.39 cc and 12 Gy marginal volume was 5.03 cc. Mean dose to brain stem, pituitary hypothalamic axis, and optic chiasm was 2.5, 0.72, and 0.49 Gy, respectively. At a median follow-up of 22 months (range 1.5-71.2 months), 7 of 10 patients presenting with a neurological deficit showed significant improvement. All 15 patients who underwent MRA 1.5-2 years after SRS had no residual nidus yielding an MRA complete obliteration rate of 100%. Twelve patients also underwent a check DSA, which confirmed obliteration in 11 of them resulting in an accuracy of MRA of 92%. One patient after SRS had transient deterioration of motor power, which resolved completely after a short course of steroids and another had mild worsening of the hemiparesis. All patients are able to lead an active functional life.
Conclusions : Careful selection of cases suitable for SRS provides optimum obliteration rates with low toxicity.

Keywords
Arteriovenous malformation, linear accelerator, micromultileaf collimator, radiosurgery