PO34 Presentation Time: 10:30 AM: Oncologic Outcomes and Toxicities in Gynecologic Cancer Patients Treated with Post-Procedure MRI-Guided Interstitial Brachytherapy at a Single Institution

Abstract

<h3>Purpose</h3> High-dose rate interstitial brachytherapy (ISBT) with implantation of the Syed-Neblett template and use of three-dimensional, CT-based planning plays an important role in the management of patients with locally advanced or recurrent gynecologic cancers. ISBT is often utilized in patients with bulky disease that is not amenable to intracavitary approaches. Previous studies have suggested there is a higher risk of fistula formation in patients treated with ISBT, as high as 18% - 32%. There is a paucity of data on ureteral strictures in patients undergoing ISBT, with only one series suggesting 4.3% of patients without baseline hydronephrosis will develop ureteral stricture. The current study examines the oncologic outcomes and treatment-related toxicities associated with ISBT for patients treated at our institution. <h3>Materials and Methods</h3> We conducted a retrospective case series of all patients who received ISBT for a gynecologic cancer at our institution from January 2015 - January 2022. Patients were identified using ICD-10 and CPT codes for ISBT. Demographics, prior oncologic treatment, treatment-related toxicities, and oncologic outcomes were collected from our institution's electronic medical record (EMR). Kaplan-Meier analysis was used for assessment of oncologic outcomes. <h3>Results</h3> Thirty patients treated with external beam radiation (EBRT) and ISBT were identified, with twenty-six patients (86.7%) treated for primary disease. The most common malignancy was cervical (N = 19, 63.3%). The most common malignancy histology was squamous cell carcinoma (N = 21, 70%). Most patients had either stage III or stage IV disease at the time of ISBT (N = 22, 73.3%). Eleven patients (36.7%) had percutaneous nephrostomy (PCN) or ureteral stent (US) placed prior to their EBRT. Twenty-nine (96.7%) had no previous history of RT. Of these cases, twenty-six (86.7%) underwent post-procedural MRI-guided ISBT to a median dose of 2750 cGy (1400 - 3250 cGy) over mostly 5 fractions. Median follow-up was 9 months (range 1 day - 4 years); disease-free survival was 61.1% at 1 year and 50.9% at 2 years, with overall survival of 84% at 1 year and 63% at 2.5 years. Univariate analysis did not reveal any significant predictors of improvement in disease-free survival based on baseline characteristics. Five patients (16.7%) required a PCN or US after treatment, only one (out of 19, 5.3%) of whom did not have pre-treatment PCN/US. Three patients (10%) developed post-treatment fistula. The most common toxicities noted included vaginal symptoms (N = 20, 66.7%), post-treatment pain (N = 18, 60%), urinary symptoms (N = 15, 50%), and rectal symptoms (N = 10, 33.3%). <h3>Conclusions</h3> MRI-guided ISBT using the Syed-Neblett template provides effective disease control and tolerable toxicity in this high-risk patient cohort. While risk of new ureteral stricture was similar to previous series, rates of fistula formation were lower than historical controls.