Adjuvant radiotherapy use after radical cystectomy in muscle-invasive bladder cancer: A survey of U.S. radiation oncologists.

369 Background: Historic trials suggested significant toxicity with adjuvant radiotherapy (ART) after radical cystectomy for muscle-invasive bladder cancer (MIBC). However, recent trials have found improved locoregional control and the 2016 NCCN guidelines recommend ART consideration for select patients at high risk of local recurrence. ART practice patterns among U.S. radiation oncologists (ROs) are unknown, and we performed a survey to explore current trends. Methods: We conducted a survey of U.S. ROs regarding the management of patients with cT2-3N0M0 transitional cell MIBC. Responses were reported using descriptive statistics. Chi-square and univariate logistic regression (UVA) of clinical and demographic covariates were conducted, followed by multivariable logistic regression analyses (MVA) to identify factors predicting for ART use. Results: 277 ROs completed our survey. Nearly half (46%) use ART for MIBC. In ART-users, indications for ART include gross residual disease (93%), positive margins (92%), pathologic nodal involvement (64%), pT3 or T4 disease (46%), lymphovascular invasion (16%), and high-grade disease (13%). On UVA, ART use was associated with the number of years in practice (p=.043), pre-cystectomy RO consultation (p=0.004), primarily treating MIBC patients fit for cystectomy (p=0.009), and intensity-modulated radiotherapy (IMRT) use (p=0.009). On MVA, routine pre-cystectomy RO consultation (odds ratio [OR] 1.91, 95% confidence interval [CI]: 1.04-3.51; p=.037) and IMRT use (OR 2.77, 95% CI: 1.48-5.22; p=.002) remained associated with ART use. Conclusions: ART use is controversial in bladder cancer, yet is unexpectedly commonly used among U.S. radiation oncologists treating patients with MIBC after radical cystectomy. NRG GU001 is a randomized trial currently accruing patients with high-risk pathologic findings for observation or ART after cystectomy, and will hopefully clarify the role of ART and help identify patients benefiting from this adjuvant therapy. Whenever possible, patients should be enrolled in this study.