The Impact of Tumor Size and Histology on Local Control when Utilizing High-Dose-Rate Interstitial Brachytherapy for Gynecologic Malignancies

Abstract

<h3>Purpose/Objective(s)</h3> To report long-term results of an outpatient template-based high dose rate interstitial brachytherapy (HDR ISBT) program for the treatment of gynecologic malignancies. <h3>Materials/Methods</h3> Patients treated at an academic hospital with outpatient template-based HDR ISBT without spinal or general anesthesia between 2006-2020 were retrospectively reviewed for this study. Patients who had previously received HDR ISBT were excluded. Baseline patient, tumor, and treatment characteristics, including tumor size, tumor histology, total EQD2 including prior external beam radiation therapy (EBRT), and/or prior chemotherapy were collected. EQD2 was calculated using an alpha/beta ratio of ten. Local control (LC) was estimated utilizing the Kaplan-Meier method. Factors associated with LC were evaluated using Cox regression analyses. <h3>Results</h3> 150 patients received HDR ISBT for a gynecologic tumor (Table 1) and median follow up time was 2.98 years (0.89-4.82). 54 local failures occurred in this patient population. Of these, 28% (15/54) were due to progression, 34% (18/54) were due to persistent disease, and 38% (20/54) were due to local recurrence. LC for all patients was 71% (64%-79%), 58% (50%-68%), and 57% (48%-67%) at one, three, and five years. LC was inferior in patients with tumors ≥3 cm (p=0.039) and non-endometrial adenocarcinoma histology (p=0.017). On multivariate analysis, non-endometrial adenocarcinoma (HR=2.423, 95% CI=1.011-5.808, p=0.047) and tumor size ≥3 cm (HR=2.903, 95% CI 1.053-3.441, p=0.033) were associated with lower LC. <h3>Conclusion</h3> The majority of patients who received outpatient-based twice daily HDR ISBT had long term LC in this series. Larger tumor size and non-endometrial adenocarcinoma histology were detrimental to LC.