To compare single-fraction 153Gd-based rotating shield brachytherapy (RSBT) for prostate cancer to conventional 192Ir-based high-dose-rate brachytherapy (HDR-BT) in a planning study which radiobiologically accounts for dose rate and relative biological effectiveness (RBE). RSBT was used for planning target volume (PTV) dose escalation without increasing urethral dose for monotherapy, or for urethral sparing without decreasing PTV dose as a boost to external beam radiotherapy.
Twenty-six patients were studied. PTV doses were expressed as equivalent dose delivered in 2 Gy fractions (EQD2), accounting for RBE (1.00 for 192Ir and 1.15 for 153Gd), dose protraction (114 minute repair half-time), and tumor dose response (α/β of 3.41 Gy). HDR-BT dose was prescribed such that 90% of the PTV received 110% of the prescription dose of 19 Gy for dose escalation and 15 Gy for urethral sparing, corresponding to EQD290% values (minimum EQD2 to the hottest 90% of the PTV) of 93.9 GyEQD2 and 60.7 GyEQD2, respectively. Twenty 90.95 GBq 153Gd RSBT sources were modeled and one 370 GBq 192Ir HDR-BT source.
For dose escalation with fresh sources, RSBT increased PTV EQD290% by 42.5% ± 8.4% (average ± standard deviation) without increasing urethral D10%, with treatment times of 216.8 ± 28.9 minutes versus 15.1 ± 2.1 minutes. After one half-life (240.4 days for 153Gd and 73.8 days for 192Ir), EQD290% increased 20.5% ± 9.1%. For urethral sparing with fresh sources, RSBT decreased urethral D10% by 26.0% ± 3.4% without decreasing PTV EQD290%, with treatment times of 133.6 ± 16.5 minutes versus 12.0 ± 1.7 minutes. After one half-life, urethral D10% decreased 20.2% ± 4.8%.
RSBT can increase PTV EQD90% or decrease urethral D10% relative to HDR-BT at the cost of increased treatment time. Source aging reduces RSBT benefit, but RSBT remains theoretically superior to HDR-BT by >20% after one-half-life has elapsed.
International journal of radiation oncology, biology, physics. 2018 Aug 06 [Epub ahead of print]
Quentin Adams, Karolyn M Hopfensperger, Yusung Kim, Xiaodong Wu, Weiyu Xu, Hemant Shukla, James McGee, Joseph M Caster, Ryan T Flynn
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242. Electronic address: ., Department of Biomedical Engineering, University of Iowa, 1402 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242., Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242., Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242; Department of Electrical and Computer Engineering, University of Iowa, 4016 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242., Department of Electrical and Computer Engineering, University of Iowa, 4016 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242., OSF Saint Francis Medical Center, 530 NE Glen Oak Ave, Peoria, Illinois, 61637.