Multisession cyberknife radiosurgery for large AVM and AVM in eloquent regions

Single-fraction stereotactic radiosurgery (SRS) is effective for small volume arteriovenous malformations (AVMs). However, large AVMs, and AVMs in eloquent regions are often not cured with SRS, because we cannot give an adequate dose to the AVMs without causing radiation damage to the surrounding normal brain tissue. We have used hypo-fractionated stereotactic radiotherapy (HFSRT) including SRS with Cyberknife (CK) for these AVMs in eloquent regions or large volume AVMs. The aim of this study is to evaluate the effectiveness of our HFSRT including SRS with CK for these AVMs with possibly a lower complication rate. During the past six years, single-fraction SRS was used as a basic treatment method for AVMs located in non-eloquent regions or for small volume AVMs. We have treated 36 cases (17 males and 19 females) of large AVMs and AVMs in eloquent regions with HFSRT, including SRS using CK. The age ranged from seven to 66 years (average 33 years). A mean marginal dose of 27 Gy (range 16-30 Gy) was prescribed and the average isodose was 76% (range 64-86%) isodose. Most patients were treated with the HFSRT method (three to five fractions) except for six SRS cases. 3-D Spoiled gradient recalled acquisition in the steady state (SPGR) MR angiography (MRA) was performed with a 3T MR scanner (Signa HDX 3.0 T, GE, US). The time-dependent relative decay of the trans-nidal blood flow and sequential volumetric reduction evidenced by 3D SPGR MRA was referred to as ''obliteration dynamics.'' All patients had periodical follow-up studies at regular intervals. Subtotal obliteration was determined if the residual nidus volume was 5% or less of the initial nidus volume. The mean follow-up period was 37 months (6-53). All patients tolerated the procedures well. After the treatment, a significant obliteration dynamics was observed in all patients over a 12-month follow-up. Subtotal obliteration was obtained in 11 patients out of 18 (61%) who had over 24-month follow-up. In conjunction with the gradual reduction of AVM volume after CK treatment, visual field defects improved, motor functions recovered and easy medical control of symptomatic epilepsy was realized in a significant number of cases. HFSRT with CK was found to be safe and effective. The use of sequential 3D SPGR MRA at 3T enables a noninvasive quantitative assessment of the dynamic obliteration process induced by HFSRT with CK in AVMs. If the long term follow-up sustains these preliminary results, HFSRT with CK could become the first treatment of choice for large AVM and eloquent regions. (author)