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Inverse Planning for Multi-Stage Robotic Stereotactic Radiosurgery for Large Cerebral Arteriovenous Malformations

C Ding

C Ding*, T Solberg, B Hrycushko, P Medin, L Whitworth, R Timmerman, UT Southwestern Medical Center, Dallas, TX

MO-F-108-4 Monday 4:30PM - 6:00PM Room: 108

Purpose: A new inverse treatment planning technique was developed for multi-staged robotic stereotactic radiosurgery of large cerebral arteriovenous malformations.

Methods:Eleven patients with large (>15 cm³) cerebral arteriovenous malformations (AVMs) were selected in this study. The AVMs were contoured and divided into 3 to 8 sub-targets with volumes of 3-7 cm³ to be treated sequentially in a staged approach at one to four week intervals. The prescription dose was 16 Gy to 20 Gy depending on the sub-target volume and location. Inverse robotic radiosurgery treatment plans were generated for the total AVM volume and optimized to achieve 95% coverage. Staged plans for individual sub-targets were generated from the total AVM plan usingthe weighting MUs based on beam lengths within each sub-targets. Forward plans were created for comparison. Dose-volume analysis was used to evaluate the PTV coverage, conformity index (CI), R50 and V12Gy values.

Results:Inverse optimization outperformed forward planning for most patients for each index considered. In eight of the eleven patients the inversely optimized plans had better target coverage (96.0+/-0.6% vs.95.8+/-1.3% for forward plan) while all of the patients had improved high dose conformality with the inversely optimized plans (1.23+/-0.16 vs. 1.44+/-0.16). Moderate dose spillage within the brain, as represented by the R50 parameter, was shown to improve in ten of the eleven patients for inversely optimized plans (3.2+/-0.7 vs. 3.9+/-0.7).

Conclusion:Inverse treatment planning for staged, robotic radiosurgery of large AVMs was shown to improve target coverage, target dose conformality, and reduce normal tissue dose compared to forward treatment planning.

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