Redefining bladder neck dose in low-dose-rate prostate brachytherapy-Can we improve urinary toxicity without impacting disease control?

BACKGROUND: We sought to assess the impact of bladder neck dose (BND) on patient reported urinary toxicity, and feasibility of relative urethral sparing technique in prostate brachytherapy (PB). METHODS AND MATERIALS: We retrospectively identified bladder neck as a point dose on post-implant CT scans in patients treated with 131Cs PB. Urinary symptoms were assessed through EPIC questionnaires. Patient cohorts were identified based on mean BND as a percentage of prescription dose with toxicity assessment at each time point. RESULTS: In our cohort of 542 patients, BND was associated with clinically significant acute urinary symptoms and chronic symptoms, as patients receiving >70% of the prescription dose had significantly worse overall EPIC scores than patients receiving ≤70% of prescription dose. There was no difference in bDFS between patients receiving BND ≤70% (96% bDFS) and >70% (94% bDFS) at a median follow up of 57 months. CONCLUSIONS: BND has a significant impact on both acute and chronic urinary symptoms, with reduced symptoms reported with BND <70% of prescription dose. With a median follow up of 4.7 years, excellent bDFS has thus far been achieved with relative urethral and bladder neck sparing. Utilizing this constraint should improve urinary symptoms without impacting disease control.

Can we reduce dose to ureters as avoidance organs for MRI based brachytherapy for cervical cancer? A dosimetric feasibility study.

BACKGROUND AND PURPOSE: Ureteral stenosis (US) is an underreported complication of brachytherapy (BT) for cervical cancer (CC), with limited data on toxicity risk reduction. A previous study demonstrated ureter EQD2 D0.1cc > 77 Gy correlated with US development. We sought to assess feasibility of this constraint while maintaining similar HR-CTV coverage. MATERIALS AND METHODS: Patients with locally advanced CC treated with EBRT plus HDR MRI-based brachytherapy boost without hydronephrosis at diagnosis and with ureter dose EQD2 D0.1cc > 77 Gy were included. Replan was attempted to achieve HR-CTV D90 ≥ 80-85 Gy and ureter dose reduction. Ureter distance from lateral margin of HR-CTV and tandem was recorded. t-test was performed to compare ureteral dose and HR-CTV D90. RESULTS: Of 25 patients were identified. Hundred percent received 45 Gy in 25 fractions to the pelvis ± paraaortic lymph nodes and 80% receiving median additional parametrial dose of 5.4 Gy. Replan meeting ureteral dose of ≤77 Gy was feasible in 18 of 25 patients, with a reduction in median ureter D0.1cc from 82.3 to 76.8 Gy (p < 0.001). Median HR-CTV D90 was similar (84.7 vs. 85.0 Gy). Replan achieved D0.1cc ≤77 Gy in 56% of patients who experienced US. All unilateral US cases occurred in the ureter closest to HR-CTV. CONCLUSIONS: Optimization to reduce ureter dose to ≤77 Gy is feasible when ureters are visible and contoured. Ureters may be considered as potential OAR during MRI-based brachytherapy treatment. Reduced ring to tandem total reference air kerma (TRAK) ratio may provide an additional metric by which to lower US risk.