Image-based Multichannel Vaginal Cylinder Brachytherapy for the Definitive Treatment of Vaginal Cancers

Abstract

Brachytherapy (BT) is integral to vaginal cancer treatment and is typically delivered using either an intracavitary single-channel vaginal cylinder or an interstitial BT (ISBT) applicator. Multi-channel vaginal cylinder (MCVC) applicators allow for improved organ-at-risk (OAR) sparing compared to single-channel applicators while maintaining target coverage and avoiding ISBT implantations in selected patients (pts). We present clinical outcomes of pts treated with image-based high-dose-rate (HDR) BT using a MCVC. Sixty pts with vaginal cancer (27% primary vaginal and 73% recurrence from gynecologic primaries) were treated with combination external beam radiotherapy (EBRT) and image-based HDR BT utilizing MCVC from 2011 to 2016. Pts were selected for treatment with MCVC only if residual disease thickness was ≤7 mm after EBRT. The BT high-risk clinical target volume (CTVHR) included the circumferential vaginal surface as defined by the length of the pre-EBRT gross tumor volume (GTV) from both imaging and clinical examination, and the post-EBRT GTV defined the area for which the entire thickness of the vagina and residual tumor would be included. Total EBRT and BT doses were summated and converted to equivalent dose in 2 Gy fractions (EQD2 Gy). All pts received 3D image-based BT to a total equivalent dose of 70-80 Gy. Nineteen pts (32%) received concurrent chemotherapy with EBRT, and 7 (12%) received adjuvant systemic therapy. After a median follow-up of 45 months (range, 11-78), complete clinical response was documented in 98% of pts. The median CTVHR volume was 24.4 cc (interquartile range [IQR], 14.1), with a median dose delivered to 90% of CTVHR of 77.2 EQD2 Gy (IQR, 2.8). The 4-year local-regional control (LRC), distant control, disease-free survival, and overall survival rates were 92.6%, 76.1%, 64.0%, and 67.2%, respectively. There were no significant differences in LRC by any of the examined patient and treatment factors. The 4-year LRC rates were similar between the primary vaginal (92%) and recurrent (93%) groups (p=0.290). Pts with lymph node positive disease had a lower rate of distant control at 4 years (22.7% vs. 89.0%, p<0.001). There were no Grade 3 or higher acute complications. The 4-year rate of late Grade 3 or higher toxicity was 2.7%. One patient developed a severe small bowel toxicity manifested as adhesions of the terminal ileum 13 months after treatment. Clinical outcomes of pts with primary and recurrent vaginal cancer treated definitively in a systematic manner with combination EBRT with image-guided HDR BT utilizing a MCVC applicator demonstrate high rates of local control and low rates of severe morbidity. The MCVC technique allows interstitial implantation to be avoided in select pts with ≥7 mm residual disease thickness following EBRT while maintaining excellent clinical outcomes with extended 4-year follow-up in this rare malignancy.