Main Session
Sep
29
PQA 06 - Genitourinary Cancer, Gynecological Cancer, and Health Care Access and Engagement
3273 - Baseline Urinary Symptom Burden, but not DIL/CTV Ratio, Correlates with Late GU Toxicity After Single-Dose Prostate Radiotherapy with Simultaneous Integrated Dominant Intraprostatic Lesion Boost
Presenter(s)
Carlo Greco, MD - CCU, Lisbon, Lisboa
C. Greco, B. Vieira, M. Simas, O. Pares, N. Pimentel, S. Vieira, J. Stroom, and Z. Fuks; Champalimaud Centre for the Unknown, Lisbon, Portugal
Purpose/Objective(s):
A simultaneous integrated boost (SIB) to the dominant intraprostatic lesion (DIL) during single-dose radiotherapy (SDRT) may improve intraprostatic control. The risk of treatment-related toxicity may depend on the proportion of prostate target volume receiving dose escalation. We assessed whether relative boosted lesion burden (dominant intraprostatic lesion-to-prostate clinical target volume ratio, DIL/CTV) is associated with urinary toxicity after whole-gland SDRT with DIL-SIB, and whether baseline urinary function provides stronger risk stratification. We hypothesized that a higher relative boosted lesion volume would not be associated with increased acute and late genitourinary (GU) toxicity due to strict adherence to well-established institutional dose/volume constraints for the organs at risk.
Materials/Methods:
Patients with unfavorable intermediate-risk prostate cancer enrolled in an IRB-approved phase II study received whole-gland SDRT (24 Gy, single fraction) with a PSMA PET/MRI-defined DIL-SIB (26.4-30 Gy). Treatment planning involved a 20% dose reduction to the trigone area, urethra and urogenital diaphragm via dose-painting. DIL volume was defined as GTV boost and DIL/CTV (%) was calculated from planning volumes. GU toxicities were graded using CTCAE v4, and patient-reported urinary outcomes were assessed with IPSS/EPIC. Acute GU toxicity was the maximum grade within =90 days; late GU toxicity (>90 days) was derived from recorded late GU events. Logistic regression evaluated DIL/CTV (per 5% increase) for acute and late GU toxicity (any-grade and grade =2). Multivariable models adjusted for baseline IPSS and CTV.
Results:
Of 147 patients treated with 24 Gy in 1 fraction, DIL-SIB was performed in 114 unfavourable intermediate risk patients. The median DIL/CTV was 7.2% (IQR 4.7-12.3%; range 0.6-36.8%). Acute GU any-grade and grade =2 rates were 54.5% and 5.1%, respectively; late GU any-grade and grade =2 rates were 63.4% and 6.1%, respectively. There were no instances of acute or late grade 3 toxicities. DIL/CTV was not associated with acute GU any-grade (univariable OR 1.14, 95% CI 0.85-1.54, p=0.384; adjusted OR 1.11, 95% CI 0.80-1.52, p=0.539) or late GU any-grade (univariable OR 0.97, 95% CI 0.72-1.32, p=0.860; adjusted OR 0.94, 95% CI 0.66-1.33, p=0.711). In the adjusted late GU any-grade model, baseline IPSS was associated with toxicity (OR per 5 points 1.90, 95% CI 1.02-3.57, p=0.045).
Conclusion:
DIL/CTV ratio was not associated with urinary toxicity in this cohort. Baseline urinary symptom burden (IPSS) showed a stronger association with late GU toxicity and may be a more useful clinical stratifier for counseling and use of pharmacological prevention with alpha-1-adrenergic receptor antagonists.