Room: Track 3
Purpose: Knife (GK) radiosurgery is a well-established treatment for a variety of brain disorders. With many variables to adjust, the conventional manual forward planning is complicated and cumbersome, making resulting plan quality essentially rely on planners’ skills, experiences and devoted efforts. This is a concern particularly for vestibular schwannoma cases, which are more challenging for planning due to irregularly-shaped target and its proximity to brainstem and cochlea. We have recently developed a multiresolution-level inverse planning (MRL-IP) strategy to ease GK planning, and validated it on brain metastases and trigeminal neuralgia cases. In this study, we adapted this approach for vestibular schwannoma cases and evaluated its efficacy.
Methods: our approach, several rounds of optimization were performed with a progressively increased resolution used for isocenter candidates. At each round, a convex objective function which consists of target maximum and minimum dose, maximum dose of the inner and outer target shells, brainstem maximum dose, cochlea mean dose and total beam-on time (BOT), was minimized to determine optimal isocenters, collimator size and duration. The optimal isocenters and their neighbors on a finer resolution were used as new isocenter candidates for next round. Final optimization result was converted to deliverable composite shots via shot sequencing.
Results: tested our method on 21 vestibular schwannoma cases previously treated at our institution. Compared to the original manual plan, we achieved significant plan quality improvement in 7 cases, moderate improvement in 6 cases, negligible improvement in 8 cases. Averaged over all the cases, our approach yielded better selectivity (0.73±0.08 versus 0.64±0.12), better CI50 (4.23±0.74 versus 4.79±1.30), lower cochlea mean dose (4.9±2.6Gy versus 5.4±2.8Gy) and shorter BOT (34.9±7.6 min versus 38.9±11.0 min) without sacrificing target coverage and brainstem dose.
Conclusion: results have demonstrated that MRL-IP approach yields much higher GK plan quality for vestibular schwannoma, compared to manual forward planning.
Funding Support, Disclosures, and Conflict of Interest: Supported by Winship Cancer Institute #IRG-17-181-06 from the American Cancer Society