Outcomes of medically inoperable endometrial cancer treated with Y-tandem brachytherapy

Summary: Our goal was to evaluate the dosimetry, toxicity, and outcomes of medically inoperable endometrial cancer patients treated with Y-tandem brachytherapy with or without external beam radiation therapy (EBRT). A retrospective chart review was performed to identify patients with medically inoperable endometrial cancer who underwent Y-tandem brachytherapy from 2009 to 2023 2024 at the University of Louisville Brown Cancer Center. Patient demographics and tumor characteristics were collected. Radiation dosimetry data analyzed included prior doses of EBRT, total doses to the High Risk-Clinical Target Volume (recorded as HR-CTV D90), and total doses to the surrounding organs at risk (recorded as D2cc in equivalent dose in 2 Gy fractions). Toxicities were defined using the Common Terminology Criteria for Adverse Events (version 5.0). Outcomes evaluated included overall survival (OS) and recurrence free survival (RFS) after the completion of brachytherapy. A total of 21 patients were included in the study. Average patient age at the completion of brachytherapy was 60.6 years old [range 27-72 years]. Average BMI, Charlson Comorbidity Index, and KPS at the initiation of brachytherapy were 50.8 [SD 14.8], 5.7 [SD 2.0], and 77 [SD 13], respectively. All patients received EBRT prior to brachytherapy, except 1 patient underwent EBRT after brachytherapy, and 2 patients received brachytherapy alone. EBRT doses ranged from 33 to 50.4 Gy (in 11 to 28 fractions). Brachytherapy doses ranged from 14.48 to 34 Gy (in 2 to 4 fractions) with a mean of 7.95 Gy per fraction. The mean HR-CTV D90 was 61.5 Gy [SD 8.9]. Average total treatment time with EBRT and brachytherapy was 59 days [IQR 49-68 days]. The mean D2cc values to the surrounding organs at risk were: 88.5 Gy [SD 28] to the bladder, 67.1 Gy [SD 23.7] to the small bowel, 70.6 Gy [SD 9.4] to the sigmoid colon, and 59.5 Gy [SD 14.4] to the rectum. Within 6 months of completion of brachytherapy, grade 3 gastrointestinal (GI), genitourinary (GU), and vaginal toxicities were noted in 3 (14%), 0 (0%), and 2 (10%) patients, respectively. Late grade 3 GI, GU, and vaginal toxicities beyond 6 months after brachytherapy completion were observed in 2 (13%), 1 (7%), and 1 (7%) patients, respectively. No patient experienced grade 4 or 5 toxicity. Two-year OS and RFS rates were 82% and 90%, respectively. There was a trend toward decreased overall survival with longer total treatment duration (p=0.081). Y-tandem brachytherapy with or without EBRT can be used to treat medically inoperable endometrial cancer patients with a minimal risk of severe toxicity. Overall survival may be decreased with extended overall treatment time. Caitlin Reichard (she/her/hers), BA, MA (Presenting Author) - University of Louisville School of Medicine; Jeremy Gaskins, PhD (Co-Author) - University of Louisville Dept of Bioinformatics & Biostatistics; Maxwell Kassel, MS (Co-Author) - South Florida Proton Therapy Institute; Andres Portocarrero Bonifaz, MS (Co-Author) - CARTI; Scott Silva, MD, PhD (Co-Author) - University of Louisville Dept of Radiation Oncology