JRSBRT 9.4, p. 313-323

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Optimizing prostate cancer SBRT: Acute GU toxicity outcomes of urethral delineation methods
Gargi Sharma, Susovan Banerjee, Tejinder Kataria, Richa Arunendu, Deepak Gupta, Shyam Bisht, Kushal Narang, Mayur Mayank, Sorun Shishak, Brij Bhushan and Susan K Abraham

Background and purpose: Precise urethral delineation is critical for minimizing genitourinary (GU) toxicity in prostate SBRT. This study compares acute toxicity outcomes between catheter-based and MRI-based urethral delineation methods.

Materials and methods: In this prospective study (2023-2024), 40 patients were randomized to catheter-based (n = 20) or MRI-based (n = 20) urethral delineation prior to SBRT. IPSS, QOL scores, and RTOG toxicity were assessed at baseline, treatment completion, and 1/3-month follow-ups. Dosimetric analysis included urethral BED and bladder V_{18 Gy}.

Results: Both methods achieved comparable dosimetric precision (urethral BED: 128 ± 12 Gy catheter vs 130 ± 10 Gy MRI, p = 0.42). Acute grade ≥2 GU toxicity rates were similar (40% catheter vs 30% MRI, p = 0.54). The catheter group showed transient QOL deterioration likely attributable to procedural discomfort, with all patients returning to baseline by 3 months. Multivariate analysis identified urethral BED ≥130 Gy (OR: 2.1, p = 0.03) and bladder V_{18 Gy} ≥ 30% (OR: 1.9, p = 0.04) as independent predictors of toxicity.

Conclusion: Catheter-based and MRI-based delineation demonstrate equivalent dosimetric and clinical outcomes in prostate SBRT. While catheterization may cause temporary discomfort, both methods are equally effective when adhering to dose constraints (urethral BED: <130 Gy, bladder V_{18 Gy} < 30%). The choice between techniques may consider patient tolerance and institutional protocols, as both approaches provide excellent therapeutic outcomes.

Keywords: prostate SBRT, urethral delineation, MRI-based planning, catheter-based planning, genitourinary toxicity