Gynecologic Oncology Computed tomographyeplanned interstitial brachytherapy for locally advanced gynecologic cancer: Outcomes and dosimetric predictors of urinary toxicity

PURPOSE: To identify dosimetric predictors of outcome and toxicity in patients receiving CT-planned interstitial brachytherapy (ISBT) for gynecologic cancers. METHODS AND MATERIALS: Patients who received ISBT between 2009 and 2014 were reviewed. Demographic, disease specific, treatment, and toxicity data were collected. Logistic regression was used to model toxicity. A least absolute shrinkage and selection operator penalty was used to identify relevant predictors. Receiver operating characteristic curves were used to analyze the relation between dosimetric factors and urinary toxicity. RESULTS: Seventy-three patients received ISBT (21 at time of cancer recurrence and 52 at the first presentation). Thirty-six patients had cervical cancer, 16 had vaginal cancer, 13 had uterine cancer, and 8 had vulvar cancer. ISBT was performed using both high-dose-rate and low-dose- rate 192 Ir sources (27 low dose rate and 46 high dose rate). With a median followup of 12 months, Grade 3 vaginal, urinary, and rectal toxicity occurred in 17.8%, 15.1%, and 6.8% of patients, respectively. No patients experienced Grade 4 or 5 toxicity. Dose to 0.1cc of urethra predicted for development of Grade 3 urinary toxicity (area under the curve of 0.81; 95% confidence interval: 0.66, 0.96). A 10% probability of a Grade 3 urinary toxicity associated with a dose of 23.1 equiv- alent dose in 2 Gy fractions (95% confidence interval: 9.51, 36.27 equivalent dose in 2 Gy fractions). CONCLUSIONS: ISBT is a safe treatment for gynecologic malignancies. The dose to 0.1cc significantly predicts for severe urinary toxicity. Our data suggests that dose to a small urethral vol- ume may be the most significant predictor of urinary toxicity in patients receiving ISBT for gyne- cologic cancer. 2016 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.