Purpose: To present and quantify the effectiveness of a method for the efficient, economically-feasible, production of Â¹â?¶â?¹Yb (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) Â¹â?¹Â²Ir source. The proposed approach could make novel brachytherapy delivery techniques that require a substantially lower-energy photon spectrum than Â¹â?¹Â²Ir 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 Â¹â?¶â?¹Yb source activation and re-activation using thermal neutrons in a research reactor and Â¹â?¶â?¸Yb-Ybâ‚‚Oâ‚ƒ precursor is derived and benchmarked against published data. The model is dependent primarily on precursor Â¹â?¶â?¸Yb enrichment percentage, active source volume, and average thermal neutron flux within the active source.
Results: Efficiency gains in Â¹â?¶â?¹Yb 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 Ã— 10Â¹â?´ n cmâ?»Â² sâ?»Â¹, increasing the source volume from 1 mmÂ³ to 3 mmÂ³ decreased reactor-days needed to generate one clinic-year of Â¹â?¶â?¹Yb from 256 to 59, and 82%-enriched precursor needed dropped from 80 mg yâ?»Â¹ to 21 mg yâ?»Â¹. A resource reduction of 74-77% is predicted for a source volume increase from 1 mmÂ³ to 3 mmÂ³.
Conclusion: Dramatic cost savings are achievable in Â¹â?¶â?¹Yb source production costs through re-activation if active sources larger than 1 mmÂ³ 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.