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169 Yb-based rotating shield brachytherapy for prostate cancer
Quentin Adams1, Karolyn M Hopfensperger2, Yusung Kim1
1Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa, 52242, USA.
Medical Physics
|October 14, 2020
Summary
This study introduces a novel 169 Yb-based rotating shield brachytherapy (RSBT) system for prostate cancer treatment. The innovative RSBT system offers improved dose escalation and urethral sparing compared to conventional HDR-BT, with shorter treatment times.
Area of Science:
- Radiation Oncology
- Medical Physics
- Urologic Oncology
Background:
- Prostate cancer treatment often involves brachytherapy, with high-dose-rate brachytherapy (HDR-BT) using 192 Ir being a common method.
- Conventional HDR-BT has limitations in dose escalation and sparing organs at risk, such as the urethra.
- A novel approach using 169 Yb-based rotating shield brachytherapy (RSBT) is proposed to overcome these limitations.
Purpose of the Study:
- To present a new system for single-fraction prostate cancer treatment using 169 Yb-based RSBT with a robotic delivery system.
- To compare the efficacy of this RSBT system against conventional 192 Ir-based HDR-BT in treatment planning studies.
- To evaluate the system's potential for dose escalation and urethral sparing in prostate cancer radiotherapy.
Main Methods:
- Treatment plans were created for 26 patients for dose escalation (20.5 Gy) and urethral sparing (15 Gy) scenarios.
- The RSBT system utilized a 999 GBq (27 Ci) 169 Yb source, while HDR-BT used a 370 GBq (10 Ci) 192 Ir source.
- A prototype robotic delivery system with an angular drive for helical source delivery was constructed and tested for mechanical accuracy.
Main Results:
- For dose escalation, RSBT achieved a 29.9% increase in PTV D90% compared to HDR-BT, with treatment times of 51.4 min vs 15.8 min.
- For urethral sparing, RSBT reduced urethral D10% by 23.1% compared to HDR-BT, with treatment times of 30.0 min vs 12.3 min.
- Mechanical accuracy measurements showed positional differences within 0.18 mm longitudinally and 0.78° angularly.
Conclusions:
- 169 Yb-based RSBT offers significant advantages in increasing target dose coverage (PTV D90%) or reducing organ-at-risk dose (urethral D10%) compared to HDR-BT.
- The single-fraction RSBT treatment times are under 1 hour, utilizing a single-source robotic delivery system.
- The prototype helical delivery system demonstrated adequate mechanical accuracy, validating the feasibility of this approach.
