SU-E-T-251: Novel Multi-Stage Stereotactic Radiosurgery Technique for Large Cerebral Arteriovenous Malformations Using the Gammaknife System

Authors


Abstract

Purpose:

To develop a multi-stage stereotactic radiosurgery delivery technique for large intracranial arteriovenous malformations (AVM) using the Gammaknife treatment platform.

Methods:

Eleven patients having large (>15 cm3) cerebral AVMs were selected for this study. AVMs were contoured and divided into 3-8 subtargets with volumes ranging from 3–7 cm3. Each subtarget is to be treated sequentially in 1–4 week intervals between stages. The prescription dose was 16–20 Gy depending on the target volume. Gammaknife plans were retrospectively generated to treat the entire AVM target with a simulated Extend frame system that can reposition patients within a 1mm accuracy. The coordinates of each shot from the initial plan were extracted based on the shot position within the Extend frame system. Shots were then grouped based on their relative position to individual subtarget contours to generate stage-specific plans. The delivery time of each shot of a subtarget was corrected for decay of each stage to generate the same dose distribution as that of the original plan for the entire AVM. Conformality and dose-volume analysis was performed to evaluate the PITV (ratio of prescription isodose volume to target volume), R50 (ratio of 50% isodose volume to target volume), and V12Gy (percentage of brain volume receiving 12Gy or greater).

Results:

The total accumulated dose for the multi-staged treatments was shown to be equivalent to the initial plan of the entire AVM target. The Gammaknife plans resulted in an average of 95.8%±0.6 PTV coverage with a PITV of 1.06±0.07. The resulting V12Gy and R50 dose spillage values were 4.2%±2.0 and 3.2±0.4, respectively.

Conclusion:

With the Extend frame, the Gammaknife system can deliver a multi-staged conformal dose to treat large AVMs. Target dose coverage and conformality as well as normal brain toxicity measures were shown to be similar compared to that of a single fraction treatment.

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