J Yi¹*, X Wu² , Q Adams³ , K Hopfensperger⁴ , K Patwardhan⁵ , R Flynn⁶ , Y Kim⁷ , W Xu⁸ , (1) Department of Electrical and Computer Engineering, University of Iowa, Iowa City, IA, (2) Department of Electrical and Computer Engineering, University of Iowa, Iowa City, IA, (3) Department of Radiation Oncology, University of Iowa Hospitals and Clinics, Iowa City, IA, (4) Department of Radiation Oncology, The University of Iowa, Iowa City, IA, (5) Department of Radiation Oncology, University of Iowa, Iowa City, IA, (6) University of Iowa Hospitals and Clinics, Iowa City, IA, (7) College of Medicine, University Of Iowa, Iowa City, IA, (8) Department of Electrical Engineering, The University of Iowa, Iowa City, IA

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  J Yi

(Sunday, 7/14/2019)  

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 D₉₀ to further improve plan quality.

Methods: In the RSBT treatment planning system, we use single shield with 45° emission angle and radiation source ¹��Yb. 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 D₉₀; (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 cm³ regions in organ at risks (OAR), and the second planning will directly maximize D₉₀ 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 D₉₀ 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 D₉₀ 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 D₉₀ 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.

Keywords

Brachytherapy, Optimization, Treatment Planning

Taxonomy

TH- Brachytherapy: Dose optimization and planning

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