GPP06 Presentation Time: 11:15 AM

We report on recurrence patterns and prognostic features among pts treated definitively for primary vaginal cancer with placement of interstitial catheters in a magnetic resonance (MR) simulator and treatment in an adjacent brachytherapy suite. The cohort included 53 pts receiving radiotherapy (RT) for primary vaginal cancer from 9/2016-1/2022 at a single institution. Pts received external beam radiation (EBRT) plus high-dose rate brachytherapy (HDR-BT) (w/ MR guidance, Espree, Siemens, Inc.), or HDR-BT alone in the following settings: prior history of anal cancer s/p RT, early stage I, multiple co-morbidities w/ severe colitis or limited life expectancy. HDR-BT was delivered via Syed interstitial template or multichannel cylinder. Pre-procedure, pts had MR (T1-, T2-, diffusion-weighted, and dynamic contrast enhance) imaging to determine applicator required for ideal coverage. Interstitial HDR-BT pts had catheters placed in the MR room. Sequences performed post applicator insertion included T2-Space and high-res T2. Contouring of gross tumor volume (GTV), clinical target volume (CTV) of vagina, additional gynecologic organs if present (uterus, cervix), and normal tissues was performed based on an internal protocol. Interstitial cases had a subsequent CT scan to validate catheter digitization. Patient characteristics, treatment toxicity, and prognostic markers were analyzed. Kaplan-Meier (KM) estimates were generated for disease-free survival (DFS), local control (LC), and overall survival (OS). 41 pts were included. Median age was 61 yrs (range 33 - 90); median follow up was 28 months. Stage: FIGO I - 9 (22%), FIGO II - 11 (26.8%), FIGO III - 9 (22%), FIGO IV - 7 (17%), and recurrent - 5 (12.2%). 30 pts (73%) were squamous cell carcinoma, 5 pts (12.2%) were adenocarcinoma. RT with both EBRT+HDR-BT was done in 35 (85.4%) cases. 6 (14.6%) pts received HDR-BT alone. Syed interstitial implant was used for 40 (97.5%); 1 received multichannel cylinder. 33 (80%) received concurrent systemic therapy, primarily with cisplatin (24 pts). Median MR-defined CTV volume was 19.9 cm 3 (range 0.77 cm 3 - 202.1 cm 3 ). Among the pts with a measurable lesion on MRI, median pre-RT tumor size was 4.5 cm (range 1.2-16.6cm). Median size at 3-month MR was 2.8 cm (range 1.3-13.3cm). Among pts who received EBRT+HDR-BT, median total D90 EQD2 was 70.2 Gy (range 56.6-91.5Gy). Median bladder, rectum, sigmoid, and bowel total EQD2 were 62.7 Gy (range 47.9-88Gy), 59.8 Gy (range 50.7-83.5Gy), 50.3 Gy (range 39.7-78.4Gy), and 50.1 Gy (range 43.2-89.9Gy), respectfully. For the pts who received HDR-BT only, median D90 EQD2 was 39.1 Gy (range 14.3-74.5Gy). Median bladder, rectum, sigmoid, and bowel EQD2 were 24.4 Gy (range 6.7-50.5Gy), 33.6 Gy (range 2.2-37.6Gy), 9 Gy (range 1.7-20.6Gy), and 2.4 Gy (range 2.3-28.3Gy). 12 pts progressed, none with local-only failure. 6 pts (46% of recurrences) progressed in multiple sites at recurrence. Disease spread distribution includes: Distant only = 7, distant+local = 2, regional LN only = 2, regional LN+local = 1. Sites of distant recurrence were lung (5), liver (3), and brain (4). Of these recurrences, 2 were in the HDR-BT only group (liver only and lung + local) and the remaining were in the EBRT + HDR BT group. For the entire cohort, 1 year OS was 82%, 2-year OS was 67%, and median OS was 5 years. 2-year DFS was 78% and 2-year LC was 93%. For the EBRT + HDR BT cohort vs. HDR-BT only cohort, 1 year OS was 80% vs. 66%, 2-year OS was 51% vs. 50%, 2-year DFS was 77% vs. 66%, and 2-year LC was 94% vs. 83%, respectively. The most common any grade treatment-related toxicity at 90-day follow up was vaginal pain, experienced by 15/40 pts. At 180-day follow up, this decreased to 8/32 pts. 6 (14.6%) pts experienced Grade 3 toxicity; 2 treated with argon laser ablation for rectal bleeding, 2 with hyperbaric oxygen for vaginal necrosis, 1 with colostomy + ileal conduit for colovesicular+colovaginal fistula, and 1 with surgical dilation for severe vaginal stenosis. In this series, MR-guided HDR-BT for primary vaginal cancer yields high rates of local control with limited grade 3+ toxicities, but lower rates of distant control indicate consideration for systemic therapy is warranted.