title: Rapid emission angle selection for rotating-shield brachytherapy.
abstract: OBJECTIVE
  The authors present a rapid emission angle selection (REAS) method that enables the efficient selection of the azimuthal shield angle for rotating shield brachytherapy (RSBT). The REAS method produces a Pareto curve from which a potential RSBT user can select a treatment plan that balances the tradeoff between delivery time and tumor dose conformity.
  
  
  METHODS
  Two cervical cancer patients were considered as test cases for the REAS method. The RSBT source considered was a Xoft Axxent(TM) electronic brachytherapy source, partially shielded with 0.5 mm of tungsten, which traveled inside a tandem intrauterine applicator. Three anchor RSBT plans were generated for each case using dose-volume optimization, with azimuthal shield emission angles of 90°, 180°, and 270°. The REAS method converts the anchor plans to treatment plans for all possible emission angles by combining neighboring beamlets to form beamlets for larger emission angles. Treatment plans based on exhaustive dose-volume optimization (ERVO) and exhaustive surface optimization (ERSO) were also generated for both cases. Uniform dwell-time scaling was applied to all plans such that that high-risk clinical target volume D90 was maximized without violating the D2cc tolerances of the rectum, bladder, and sigmoid colon.
  
  
  RESULTS
  By choosing three azimuthal emission angles out of 32 potential angles, the REAS method performs about 10 times faster than the ERVO method. By setting D90 to 85-100 Gy10, the delivery times used by REAS generated plans are 21.0% and 19.5% less than exhaustive surface optimized plans used by the two clinical cases. By setting the delivery time budget to 5-25 and 10-30 min∕fx, respectively, for two the cases, the D90 contributions for REAS are improved by 5.8% and 5.1% compared to the ERSO plans. The ranges used in this comparison were selected in order to keep both D90 and the delivery time within acceptable limits.
  
  
  CONCLUSIONS
  The REAS method enables efficient RSBT treatment planning and delivery and provides treatment plans with comparable quality to those generated by exhaustive replanning with dose-volume optimization.
authors: Department of Electrical and Computer Engineering, University of Iowa, 4016 Seamans Center, Iowa City, Iowa 52242, USA.
authors: Yunlong
authors: Y
authors: Liu
authors: Ryan T
authors: RT
authors: Flynn
authors: Wenjun
authors: W
authors: Yang
authors: Yusung
authors: Y
authors: Kim
authors: Sudershan K
authors: SK
authors: Bhatia
authors: Wenqing
authors: W
authors: Sun
authors: Xiaodong
authors: X
authors: Wu
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D008962:Models, Theoretical; D011835:Radiation Protection; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012399:Rotation; D013997:Time Factors
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