MO‐F‐108‐04: Inverse Planning for Multi‐Stage Robotic Stereotactic Radiosurgery for Large Cerebral Arteriovenous Malformations

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.