Volume Staged Radiosurgery For Large Avms: Long Term Results And A Change In Protocol

Michael W McDermott1, Zachary Seymour2, LIJUN MA1, Martina Descovich2, David Larson3, Christopher Dowd2, Van Halbach2, Michael Lawton2, Bill Young2, Penny K Sneed, MD4

1UCSF 2UCSF, San Francisco. USA 3San Francisco, CA United States 4Dept. of Radiation Oncology, University of California San Francisco

Keywords: arteriovenous malformation, outcome, gamma knife, radiosurgery, vascular malformation

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     Radiosurgery (SRS) for large AVMs is problematic. Treatment options include fractionated or volume staged approaches.
     We describe our long term experience with volume staged radiosurgery since 1993 and an evolution to smaller volumes per stage.
     The Gamma Knife (GK) database was reviewed for volume staged radiosurgery cases between September 1992 and December 2008. Era 1 (E1) was defined as the initial experience from 1992 to 2005, Era 2 (E2) 2005-2008. There were 69 cases of intended volume-staged SRS for Spetzler-Martin grade 3-5 AVMs, 32 males and 37 females. Median age was 34 yrs. at time of treatment (range 9-68 yrs.).
     Clinical charts and treatment records were reviewed to determine the population demographics, AVM parameters, treatment data, obliteration, hemorrhages in the latent period, re-treatment and complication profiles.
      Median follow-up in the 37 living E1 patients was 50.7 mo., and 24 living E2 Patients 15.8 mo. Prior to SRS the incidence of hemorrhage 17% and seizures 27%. Median AVM AP/LAT/VERT dimensions were 4.3 / 3.5 / 3.5 cms. Median overall AVMs volumes were 20.3 cc. (range 8.6 – 70.1 cc.). In E1 1st, 2nd and 3rd stage volumes were 15.4/11.5/11.7 cc., and in E2 6.9/6.7/6.5 cc. Median prescription doses were 16 Gy for E1 and 17 Gy for E2. All patients in E2 showed some radiographic size reduction, while 2 in E1 did not. Additional treatment was required in 12 patients in E1 and 1 in E2. For the E1 patients salvage treatment included surgery in 2, repeat SRS in 8 and embolization in 2. Complications were common; 11 patients in E1 and 14 patients in E2 did not have complications. There were 8 deaths during follow-up (11.5%): 4 from AVM hemorrhage; 2 unknown cause; 1 feeding artery aneurysm rupture and; 1 nocturnal seizure.
     This is a retrospective study.
     Volume staged GKSRS is an option for large AVMs. Based on our experience with 2 or more stages, we feel that a maximum 8 – 10 cc. volume per stage is reasonable.
     Obliteration rates with larger AVMs are low and reducing AVM volume in size to make it amenable to surgical excision should be considered as success. Further data on Pollock AVM grade and obliteration will be presented.


Project Roles:

M. McDermott (), Z. Seymour (), L. MA (), M. Descovich (), D. Larson (), C. Dowd (), V. Halbach (), M. Lawton (), B. Young (), P. Sneed ()