Main Session
Sep
30
PQA 07 - Genitourinary Cancer, Patient Safety, Nursing/Supportive Care
3191 - Urethral Dose as a Predictor of Genitourinary Toxicity and Patient-Reported Quality of Life after Prostate Stereotactic Body Radiotherapy with Focal Intraprostatic Boost: Secondary Analysis of a Phase 2 Trial
Presenter(s)
Mustafa Basree, DO, MS - University of Wisconsin Hospitals and Clinics, Madison, WI
M. M. Basree1, L. Mao2, S. C. Callahan1, B. A. Morris1, N. Anger3, G. M. Cooley Jr1, J. M. Schuster1, N. J. Hurst Jr4, R. A. B. Bayliss1, Z. S. Morris1, M. A. Ritter1, and J. M. Floberg5; 1Department of Human Oncology, University of Wisconsin Hospitals and Clinics, Madison, WI, 2Department of Biostatistics, University of Wisconsin School of Medicine and Public Health, Madison, WI, 3University of Wisconsin School of Medicine and Public Health, Madison, WI, 4William S. Middleton Memorial Veterans Hospital, Madison, WI, 5Department of Human Oncology, University of Wisconsin-Madison, Madison, WI
Purpose/Objective(s):
Prostate SBRT with a simultaneous integrated boost (SIB) to MRI-identified disease improves biochemical control but has been reported to be associated with a 15-30% cumulative incidence of grade =2 genitourinary (GU) toxicity and variable impact on patient-reported quality of life (PRQoL) metrics. We hypothesize that urethral dose predicts acute and late GU toxicity and impacts urinary PRQoL. The goal of this study is to identify dosimetric predictors of GU toxicity and PRQoL after SBRT with SIB.Materials/Methods:
In this secondary analysis of a prospective phase 2 trial (NCT02470897), 114 patients with low- or intermediate-risk prostate cancer received prostate SBRT of 40 Gy in 5 fractions, with a SIB of 42.5–45 Gy to MRI-identified PI-RADS 4-5 lesions and with an attempted urethral zone constraint of 36.25 Gy. Planning objectives limited the volume of urethra, bladder, and rectum receiving 42 Gy to 0.1cc. Dosimetric variables were extracted from the dose-volume histogram (DVH) data for each subject and correlated with toxicity and PRQoL data. Toxicity evaluation included grade =2 acute and late GU toxicity (CTCAE v5.0), with the use of alpha blockers scored as grade 2. PRQoL was assessed using the Expanded Prostate Cancer Index Composite (EPIC-26). The dosimetric variables were selected based on their predictive performance for acute toxicity using the receiver operating characteristic (ROC) curve analysis. The association of the selected variables with acute toxicity, late toxicity, and QoL was evaluated using boxplots and Wilcoxon rank-sum tests. P values < 0.05 were considered statistically significant. All analyses were performed using R version 4.1.1.Results:
Among the cohort (median age 68 years; 87% intermediate-risk; median follow-up 42 months), urethral Dmax (median 39.8 Gy with grade 2+ toxicity vs. 38.8 Gy without), D5% (38.3 vs. 37.8 Gy), and D10% (38.1 vs. 37.5 Gy) were the most predictive dosimetric variables for acute toxicity (all p<0.05). There was no association of these variables with late GU toxicity. Borderline significant association of Dmax (39.9 Gy vs 39.2 Gy; p=0.064) was noted with urinary irritative/obstructive domain Score change from baseline to 24 months.Conclusion:
Urethral dose parameters predict acute but not late GU toxicity after prostate SBRT with focal SIB, with a borderline association with urinary PRQoL. Urethral dose constraints may help limit acute urinary toxicity and potentially long-term changes in PRQoL.