Radiation and Cancer Physics

MO 22 - Physics 11-Hardware Technologies and Treatment Delivery

1263 - Single-Shot 169Yb-based Rotating Shield Brachytherapy for Prostate Cancer Using a Robotic Delivery System

Wednesday, September 18
1:15 PM - 1:20 PM
Location: Room W175

Single-Shot 169Yb-based Rotating Shield Brachytherapy for Prostate Cancer Using a Robotic Delivery System
Q. Adams1, K. Hopfensperger2, Y. Kim1, X. Wu3, W. Xu3, H. Shukla4, J. L. McGee4, J. M. Caster1, and R. T. Flynn1; 1Department of Radiation Oncology, University of Iowa Hospitals and Clinics, Iowa City, IA, 2University of Iowa, Department of Biomedical Engineering, Iowa City, IA, 3Department of Electrical and Computer Engineering, University of Iowa, Iowa City, IA, 4OSF Saint Francis Medical Center, Peoria, IL

Purpose/Objective(s): To assess the potential clinical benefits of a 169Yb-based rotating shield brachytherapy (RSBT) system designed for a “single-shot” high-dose-rate brachytherapy (HDR-BT) of prostate cancer. Initial single-shot 192Ir-based HDR-BT studies have demonstrated low toxicity but inferior 6-year biochemical free survival rates to conventional regimens (82% vs 95%). RSBT may make the single-shot regimen a more durable therapy via dose escalation without adding toxicity. RSBT could also be used to deliver single-shot boosts to external beam radiotherapy with lower toxicity than conventional HDR-BT through urethral sparing.

Materials/Methods: A fully automated RSBT delivery system is presented that uses a compact six degrees-of-freedom robot to align and connect a shield control assembly to each implanted needle in series under accurate optical guidance. Following connection to a needle, the shield control assembly uses rotational motors to drive a flexible, partially-shielded catheter containing a conventional afterloader-controlled 27 Ci 169Yb source down the needle in a helical manner. Functional components critical to catheter control and system guidance are redundant to ensure safety in case of individual component malfunction. Intensity modulation is achieved through control of the angular velocity of the shielded catheter, and there is no possibility for inter-needle interference given only one shield is inside the patient at once. Treatment plans for 26 patients were created for plan goals of either dose escalation or urethral sparing, for both 192Ir-based HDR-BT and 169Yb-based RSBT. Needle placement was manually optimized. The prescription for the dose escalation plan was 20.5 Gy in 1 fraction and for the urethral sparing plan was 15 Gy in 1 fraction. Dose was prescribed such that 90% of the planning target volume (PTV) received 110% of the prescription dose.

Results: For dose escalation, with equivalent urethra D10%­, RSBT increased the PTV D90%­ to 29.5 ± 0.9 Gy (average ± standard deviation) from the HDR-BT PTV D90% of 22.5 ± 0.0 Gy, an improvement of 30.9% ± 4.1%­. Corresponding treatment times were 50.3 ± 6.2 minutes for RSBT and 15.4 ± 2.1 minutes for HDR-BT. For urethra sparing, with equivalent PTV D90%­, RSBT decreased the urethra D10% to 12.1 ± 0.5 Gy from the HDR-BT urethra D10% of 15.9 ± 0.4 Gy, a reduction of 24.1% ± 3.3%. Corresponding treatment times were 29.3 ± 3.7 minutes for RSBT and 11.8 ± 1.7 minutes for HDR-BT.

Conclusion: 169Yb-based RSBT can increase PTV D90%, without exceeding normal tissue constraints, or decrease urethral D10% relative to HDR-BT with treatment times of less than one hour. The delivery system uses a single source and could provide an effective single-shot treatment option for prostate cancer as a monotherapy or as a boost to external beam radiotherapy. An optically-guided, robotic, helical RSBT system could provide automated, efficient, and safe delivery.

Author Disclosure: Q. Adams: Research Grant; National Institute of Biomedical Imaging and Bioengineering, National Cancer Institute. Patent/License Fees/Copyright; Advanced rotating shield brachytherapy and planning of the same. K. Hopfensperger: Research Grant; National Cancer Institute, National Institute of Biomedical Imaging and Bioengineering. Y. Kim: Research Grant; Biomedical Imaging and Bioengineering, National Cancer Institute. Vice Chair; AAPM. X. Wu: Research Grant; National Cancer Institute, Biomedical Imaging and Bioengineering. Patent/License Fees/Copyright; Advanced rotating shield brachytherapy and planning of the same. W. Xu: Research Grant; Biomedical Imaging and Bioengineering, National Cancer Institute. H. Shukla: None. J.L. McGee: None. J.M. Caster: Research Grant; Biomedical Imaging and Bioengineering, National Cancer Institute. R.T. Flynn: Research Grant; National Cancer Institute, Biomedical Imaging and Bioengineering. Patent/License Fees/Copyright; Advanced rotating shield brachytherapy and planning of the same. Founder of company; pxAlpha, LLC.

Quentin Adams, MD, BS

University of Iowa Hospitals and Clinics

Disclosure:
Employment
University of Iowa Hospitals and Clinics

Compensation
National Cancer Institute: Research Grants;
National Institute of Biomedical Imaging and Bioengineering: Research Grants

Ownership
Advanced rotating shield brachytherapy and planning of the same: Patent/License Fees/Copyright

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