GSOR8 Presentation Time: 9:35 AM: Impact of External Beam Radiotherapy Site on Cervical Cancer Outcomes for Patients Undergoing Brachytherapy Boost at a Single Institution

Abstract

<h3>Purpose</h3> For patients undergoing definitive radiation treatment for cervical cancer, historical evidence demonstrates that a delay in overall time to complete therapy beyond 7-9 weeks yields poorer survival outcomes. Moreover, retrospective data suggests that treatment with external beam radiotherapy (EBRT) and HDR brachytherapy at different institutions corresponds to increased likelihood of treatment delays and worse survival. It is unclear, however, whether these treatment-related factors continue to impact cervical cancer outcomes in contemporary cohorts with modern diagnostic imaging and treatment techniques. We investigated treatment-related factors and associated outcomes in a contemporary cohort of patients undergoing definitive radiation treatment for cervical cancer. <h3>Materials and Methods</h3> We conducted a retrospective cohort study using a single institution treatment database to identify patients who underwent HDR brachytherapy as part of definitive radiation treatment for cervical cancer between 2011 and 2021. Patients were categorized as having undergone EBRT at the same institution or at an outside facility. Patients who initially underwent surgery with hysterectomy were excluded. All patients underwent staging using PET and/or MRI imaging modalities and underwent MRI prior to HDR brachytherapy as well as CT and/or MRI with brachytherapy. We utilized Cox regression models to analyze the impact of treatment-related factors on recurrence-free and overall survival. <h3>Results</h3> The observational cohort included N = 138 patients with cervical cancer who underwent HDR brachytherapy as part of definitive radiation treatment during the study period including 64 (46.4%) who underwent EBRT at an outside facility. The majority of patients (72%) had FIGO 2018 Stage III or IV disease at diagnosis and median tumor size was 5.3 cm in greatest dimension (IQR: 4.0-6.5). Nearly all patients (95.6%) received concurrent chemotherapy. Median total treatment time was 50 days (IQR: 46-57). Patients who underwent outside EBRT were more likely to have a treatment delay of >8 weeks total treatment time (56% vs. 9%, p < 0.001). At a median follow up of 34 months, outside EBRT was not associated with a difference in recurrence-free survival (HR 0.97, 95% CI: 0.49-1.93) or overall survival (HR 0.96, 95% CI: 0.43-2.15) on univariate or multivariate analyses. Similarly, no difference in outcomes was observed when stratifying analyses by tumor size (> or < 5 cm) or stage at diagnosis. <h3>Conclusions</h3> In this observational cohort patients undergoing HDR brachytherapy for cervical cancer at a single institution, there was no difference in outcomes based on whether EBRT was delivered at the same facility despite outside EBRT being associated with increased total treatment time. Future prospective studies should investigate the optimal window of total treatment time for patients with cervical undergoing definitive radiation treatment in the era of modern diagnostic modalities, contemporary HDR technique, and concurrent chemotherapy.