640 Comparing adjuvant external beam radiotherapy with brachytherapy to external beam radiotherapy alone in intermediate-risk cervical cancer

Introduction/Background Patients with intermediate risk cervical cancer receive external beam radiotherapy as adjuvant treatment to improve disease free survival, however the brachytherapy boost is an option in clinical practice without proven oncologic benefits. We assessed the impact of brachytherapy boost with external beam radiotherapy on overall survival in patients with intermediate-risk, early-stage cervical cancer after radical hysterectomy. Methodology A retrospective cohort study was performed using data collected from the National Cancer Database. Patients with cervical cancer from 2004 to 2019 who underwent a radical hysterectomy and lymph node staging and had disease limited to the cervix but with tumors larger than 4 cm or ranging from 2 to 4 cm with positive lymphovascular space invasion(LVSI) were selected for analysis. Patients who underwent external beam radiotherapy alone and those who underwent external beam radiotherapy plus brachytherapy boost were compared after 2:1 propensity score matching. A subgroup analysis was conducted, considering histology types, LVSI, surgical approach, and use of chemotherapy. Additionally, we evaluated potential unmeasured confounding using a sensitivity analysis with the E-value. Results In total, 1,302 patients met the inclusion criteria: 960(73.7%) received external beam radiotherapy, and 342(26.3%) received external beam radiotherapy and brachytherapy boost. After 2:1 propensity score matching, we included 675 patients in the external beam radiotherapy group and 339 in the brachytherapy boost group. Overall survival did not differ between the patients who received external beam radiotherapy alone and those who received the brachytherapy boost (hazard ratio, 0.94 95% CI, 0.69–1.28; p=0.7). In the subgroup analysis outcomes, brachytherapy boost was not associated with a significant improvement in overall survival. The E-value to shift the upper confidence limit to 0.99 was 1.90. Conclusion The use of brachytherapy boost after external beam radiotherapy in patients with intermediate-risk cervical cancer following radical surgery and lymph node assessment is not associated with improved overall survival. Disclosures No disclosures.