LBA5503 Background: Pelvic external beam radiotherapy (EBRT) reduces the risk of vaginal and pelvic recurrence for stage I endometrial carcinoma (EC), but without survival benefit. In the PORTEC1-trial, the 5-year risk of vaginal and pelvic recurrence for high- intermediate risk patients was 19% without further treatment, compared to 5% after EBRT. Most recurrences were located in the upper vagina. Phase II trials suggested vaginal brachytherapy (VBT) to be as effective as EBRT. PORTEC-2 is the first randomized trial comparing the efficacy of VBT and EBRT to determine which treatment provides optimal local control with best quality of life. Methods: The PORTEC-2 trial was a multicenter phase-III trial. After surgery, patients were randomly allocated (1:1) to pelvic EBRT (46 Gy in 23 fractions) or VBT (21 Gy HDR in 3 fractions, or 30 Gy LDR). Eligible patients had a high-intermediate risk EC: age > 60 and stage 1C grade 1–2 or stage 1B grade 3; any age and stage 2A grade 1–2 or grade 3 with < 50% invasion....