Room: ePoster Forums
Purpose: To compute an optimized brachytherapy treatment plan under a given treatment time budget, to greatly reduce treatment time of rotating shield brachytherapy (RSBT) for cervical cancer without compromising plan quality, and to directly optimize Dâ‚‰â‚€ to further improve plan quality.
Methods: In the RSBT treatment planning system, we use single shield with 45Â° emission angle and radiation source Â¹â?¶â?¹Yb. We introduce a time budget constraint in the treatment planning and model the problem as a quadratic optimization which is solved by CPLEX. We investigate the tradeoff between treatment time and plan quality. We further introduce another novel second stage planning to achieve the following goals: (1) directly optimize Dâ‚‰â‚€; (2) explicitly constrain the scaling factor to be 1. The first model provides guidance for defining a hottest 90% region in high-risk clinical target volume (HR-CTV) and hottest 2 cmÂ³ regions in organ at risks (OAR), and the second planning will directly maximize Dâ‚‰â‚€ under the tolerance constraints for OARs and treatment time constraint.
Results: We validate our algorithms via experiments on 5 patient cases. The results show that on average, when we reduce the delivery time from 45.85 min to 37.10 min and 28.14 min, the Dâ‚‰â‚€ will decrease from 88.12 Gy to 86.10 Gy and 81.98 Gy correspondingly. The results also show that on average, the second planning can further improve the Dâ‚‰â‚€ from 88.12 Gy to 90.47 Gy.
Conclusion: This work shows that significant reduction in treatment time is possible without compromising the quality of treatment plan. By introducing a second stage planning, the Dâ‚‰â‚€ can be further improved.
Funding Support, Disclosures, and Conflict of Interest: The authors acknowledge funding from the National Institute of Biomedical Imaging and Bioegineering (R01 EB020665) and the National Cancer Institute Phase 1 Small Business Technology Transfer grant (1 R41 CA210737-01). Ryan Flynn has ownership interest in pxAlpha, LLC, which is developing a commercial rotating shield brachytherapy system.