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Enabling Rotating Shield Brachytherapy with Efficient Yb-169 High-Dose-Rate Brachytherapy Source Production by Re-Activation

R Flynn1*, Q Adams1, K Hopfensperger2, X Wu1,3, W Xu3, Y Kim1, (1) Department of Radiation Oncology, The University of Iowa, Iowa City, IA, (2) Department of Biomedical Engineering, The University of Iowa, (3) Department of Electrical and Computer Engineering, The University of Iowa


(Sunday, 7/14/2019) 2:00 PM - 3:00 PM

Room: 301

Purpose: To present and quantify the effectiveness of a method for the efficient, economically-feasible, production of ¹��Yb (93 keV average photon energy) high-dose-rate brachytherapy (HDR-BT) sources with a 27 Ci (999 GBq) activity upon clinical delivery. Such a source would have about the same dose rate at 1 cm off-axis in water as a 10 Ci (370 GBq) ¹�²Ir source. The proposed approach could make novel brachytherapy delivery techniques that require a substantially lower-energy photon spectrum than ¹�²Ir possible, such as rotating shield brachytherapy (RSBT). RSBT may provide needle-free brachytherapy for cervical cancer without loss in tumor coverage relative to intracavitary/interstitial HDR-BT and significant dose escalation and/or urethral sparing for prostate cancer relative to HDR-BT.

Methods: A theoretical framework for ¹��Yb source activation and re-activation using thermal neutrons in a research reactor and ¹��Yb-Yb₂O₃ precursor is derived and benchmarked against published data. The model is dependent primarily on precursor ¹��Yb enrichment percentage, active source volume, and average thermal neutron flux within the active source.

Results: Efficiency gains in ¹��Yb source production are achievable through re-activation, and the gains increase with source volume. For an average thermal neutron flux within the active source of 1 × 10¹� n cm�² s�¹, increasing the source volume from 1 mm³ to 3 mm³ decreased reactor-days needed to generate one clinic-year of ¹��Yb from 256 to 59, and 82%-enriched precursor needed dropped from 80 mg y�¹ to 21 mg y�¹. A resource reduction of 74-77% is predicted for a source volume increase from 1 mm³ to 3 mm³.

Conclusion: Dramatic cost savings are achievable in ¹��Yb source production costs through re-activation if active sources larger than 1 mm³ are used. Source wire diameter does not need to be increased to support this approach, thus the source could be used with commercially available afterloaders.

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 develop a commercial rotating shield brachytherapy system.


Brachytherapy, HDR, Activation


TH- Brachytherapy: Development (new technology and techniques)

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