3337 - Comparing Urethral Delineation Methods in Prostate SBRT: Impact on Acute GU Toxicity

12:45pm - 02:00pm PT

Hall F

Screen: 23

POSTER

Presenter(s)

Tejinder Kataria, MD, DNB, CCST - Medanta-The Medicity, Gurgaon, Haryana

G. Sharma, S. Banerjee, T. Kataria, D. Gupta, R. Arunendu, S. Shishak, S. S. Bisht, K. Narang, and M. Mayank; Medanta Cancer Institute, Medanta-The Medicity, Gurgaon, India

Purpose/Objective(s):

Stereotactic Body Radiation Therapy (SBRT) delivers precise, high-dose treatment for prostate cancer, leveraging unique radiobiology. However, the proximity of the urethra and bladder presents challenges, with urethral dose exposure playing a critical role in acute genitourinary (GU) toxicities that affect quality of life (QOL). Accurate urethral delineation during treatment planning is essential, yet limited evidence exists comparing catheter-based and MRI-based methods. This study evaluates these techniques' impact on acute GU toxicity, focusing on International Prostate Symptom Score (IPSS), QOL changes, and dosimetric predictors. Findings aim to optimize SBRT protocols and improve patient outcomes.

Materials/Methods:

This prospective study included 40 patients with localized prostate cancer treated with SBRT at a single Institute (2023–2024). Patients were randomized into catheter-based (Catheter Arm) and MRI-based (MRI Arm) urethral delineation groups. IPSS, QOL scores, and Radiation Therapy Oncology Group (RTOG) toxicity grades were recorded at baseline, end of treatment, and 1- and 3-month follow-ups. Dosimetric parameters, including urethral biologically effective dose (BED), bladder dose constraints, prostate volume, and diabetes status, were analyzed to identify predictors of acute toxicity.

Results:

Both groups showed significant increases in IPSS and QOL scores at treatment end and 1-month follow-up, returning to baseline by 3 months. No significant differences in IPSS worsening or QOL deterioration were observed between groups (p > 0.05). Grade =2 GU toxicity rates were comparable (40% in the Catheter Arm vs. 30% in the MRI Arm, p = 0.54). Urethral BED =130 Gy and bladder V18Gy =30% were independent predictors of acute Grade =2 toxicity.

Conclusion:

Catheter-based and MRI-based methods demonstrated similar acute GU outcomes. While there was a trend toward worse QOL outcomes in the Catheter Arm, likely due to temporary discomfort, both methods remain effective for SBRT planning. Adherence to urethral BED and bladder constraints is crucial for minimizing toxicity and optimizing outcomes.