ESTRO 2021 Abstract Book

S346

ESTRO 2021

nodes to the total lymph nodes removed, and other clinicopathological factors in patients with stage IIIC endometrial cancer (EC) and a pure endometrioid histology. Materials and Methods The clinical data for 397 patients with stage IIIC EC treated with postoperative radiotherapy were retrospectively analyzed. The inclusion criteria were biopsy-proven endometrial adenocarcinoma or a non- endometrioid histology, patients with FIGO stage IIIC1 or IIIC2 EC, and patients receiving postoperative adjuvant RT. Patients with stage IV disease, those who had fewer than 10 lymph nodes removed, patients who received chemotherapy before surgery, and patients unable to receive adjuvant RT were excluded from the study. The median number of dissected and metastatic lymph nodes were 38 and 3, respectively. Factors effecting overall survival (OS) and progression-free survival (PFS) were assessed. Results The median age of patients in the entire cohort was 61 years (range 34–88 years). The predominant histology was endometrioid adenocarcinoma. The median number of dissected and metastatic lymph nodes were 38 (range, 10–162 nodes) and 3 (range, 1–61 nodes), respectively, in the entire cohort. The 5-year OS and PFS rates were 58% and 52%, respectively, with a median follow-up time of 35.7 months. The LNR cut-off values were 9.6% and 8.7% for the entire cohort and patients with a pure endometrioid histology, respectively. The 5- year PFS rates in patients with LNRs less than 9.6% and greater than or equal to 9.6% were 65% and 42%, respectively (p < 0.001). The 5-year PFS rates were significantly higher in patients with an LNR less than 8.7% compared with those with an LNR greater than or equal to 8.7% for the entire cohort (75% vs. 47%, p < 0.001) In the univariate analysis, age, histology, tumor grade, cervical stromal invasion, and adjuvant chemotherapy were significant prognostic factors for both OS and PFS. In the multivariate analysis, advanced age (≥ 60 years), grade III tumor, presence of cervical stromal invasion, higher LNR, and lack of adjuvant chemotherapy were independent predictors for worse OS and PFS. Conclusion We demonstrate that the LNR is an independent predictor for OS and PFS in patients with stage IIIC EC treated with postoperative radiotherapy. Together with high LNR values, older patients with a high tumor grade, cervical stromal involvement, and lack of adjuvant chemotherapy were candidates for intense adjuvant therapy and close follow-up. PH-0447 Dosimetric predictor of urinary and bowel toxicity for exclusive adjuvant vaginal cuff brachytherapy E. Cerezo Druet 1 , N. Sanmamed 2 , Z. Aza 3 , M. Fuentes 4 , L. Gomez 2 , M. Gaztañaga 2 , P. Coronado 5 , A. Doval 2 , J. Corona 2 , G. Vázquez 2 1 Hopsital Clinico San Carlos, Radiation Oncology, Madrid, Spain; 2 Hospital Clinico San Carlos, Radiation Oncology, Madrid, Spain; 3 Hospital Clinico San Carlos, Medical Physics , Madrid, Spain; 4 Hospital Clinico San Carlos, Preventive department, Madrid, Spain; 5 Hospital Clinico San Carlos, Gynecology and obstetrics, Madrid, Spain Purpose or Objective Adjuvant vaginal cuff brachytherapy (VBT) provides excellent local control in patients with early stage endometrial cancer (EC). Due to the low toxicity reported in EC patients treated with VBT alone, to our knowledge, there are no dose constraints to the organs at risk described in the literature. We purpose to evaluate toxicity of exclusive VBT in EC patients and to assess its relation with dosimetric parameters. Materials and Methods Eighty-three patients with FIGO Stage I EC treated with VBT alone from 2014 to 2019 were retrospectively analyzed. All patients underwent total hysterectomy and bilateral salpingo-oopherectomy ± lymph node dissection followed by VBT 21Gy/3 fractions to the upper ⅓ of the vagina (4 cm) at 5 mm depth, delivered weekly. Gastrointestinal (GI) and genitourinary (GU) toxicity was evaluated using Common Terminology Criteria for Adverse Events (CTACE) version 4.0 and classified into acute and late according to whether they appeared before or after 6 months of VBT. Maximum dose (Dmax) and dose received by 2 cc(D 2cc ) of bladder and rectum were collected and descriptive analysis was performed. Chi Square test was used to assess the impact of dosimetric parameters on toxicity. Overall survival was calculated using Kaplan-Meier plots. Results Median age was 68. Thirty-five patients (42,2%) were FIGO Stage IA and 48 (57,8%) stage IB. With a median follow-up of 36 months acute GI and GU grade 1 toxicity was presented in 13 patients (15,7%) and 36 (43,4%), and grade 2 in 4 patients (4,8%) and 1 (1,2%) respectively. One patient (1,2%) presented grade 3 acute GI toxicity (fecal urgency due to proctitis) and 2 patients (3,6%) developed grade 3 acute GU toxicity (urinary incontinence). Late GI and GU grade 1 toxicity was presented in 15 patients (18, 7%) and 37 (44, 6%), and grade 2 in 2 patients (3,6%) and 5 (6%) respectively. One patient (1, 2%) had grade 3 late GU toxicity (urinary incontinence) (Fig 1). Grade 1 vaginal stenosis was developed in 16 patients (19,3%) and grade 2 in 1 (1,2%). Four patients presented (4,9%) chronic dyspareunia. Median Dmax and D 2cc in rectum were 6.43Gy (IQR: 5,54- 7,14) and 4,46 (IQR: 3,71- 5,01) respectively, and median Dmax and D 2cc in bladder were 6.68Gy (IQR: 6,05- 7,47) and 5.29 (IQR: 4,70-5,68). Statistically significant association was observed in both acute (p=0.048) and late (p= 0.05) GU toxicity with bladder Dmax > 7.46Gy and D 2cc > 5.67Gy. Patients who presented grade 3 GU toxicity were in the highest Dmax and D 2cc quartile. No significant association was observed in acute or late GI toxicity with rectal doses. Local and distant recurrence rate was 3,6% and 4,8% respectively, and overall survival was 91%.