ESTRO 2025 - Abstract Book

S802

Clinical - Gynaecology

ESTRO 2025

Oncology, Osaka International Cancer Institute, Osaka, Japan. 19 Department of Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan. 20 Department of Gynecology, Gunma Prefectural Cancer Center, Gunma, Japan. 21 Department of Gynecology, Kanagawa Cancer Center Hospital, Kanagawa, Japan. 22 Department of Gynecology, Osaka International Cancer Institute, Osaka, Japan. 23 Department of Obstetrics and Gynecology, Institute of Medicine, University of Tsukuba, Ibaraki, Japan. 24 Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto, Japan Purpose/Objective: Two randomized controlled trials (RTOG1203 and PARCER) have demonstrated that pelvic radiotherapy using intensity-modulated radiotherapy (IMRT) can significantly reduce acute and chronic bowel toxicity compared to 3D conformal radiotherapy (3DCRT) in patients with postoperative uterine corpus/cervical cancer. However, non inferiority in oncologic outcomes of IMRT has not been investigated for high-risk cervical cancer patients in a prospective trial setting. Therefore, we conducted a single-arm confirmatory trial of postoperative concurrent chemoradiotherapy using IMRT (IMRT-CCRT) for patients with high-risk uterine cervical cancer. Material/Methods: This trial enrolled patients with FIGO 2008 stage IB1, IB2, IIA1, IIA2, and IIB cervical cancer who underwent radical hysterectomy. Patients were required to have histologically confirmed positive pelvic lymph nodes or parametrial invasion, while those with positive surgical margins were excluded. IMRT was administered with a total planning target volume D50 of 50.4 Gy in 28 fractions. The clinical target volume included the vaginal cuff, paracolpium, and pelvic lymph node region. Chemotherapy with cisplatin (40 mg/m²) was administered once weekly during radiotherapy for 5 courses. The primary endpoint was 3-year relapse-free survival (RFS). The planned sample size was 220 patients, calculated based on an expected 3-year RFS of 76%, a threshold of 68%, a one-sided alpha of 5%, and a power of 80%. The key secondary endpoint was the incidence of ≥grade 3 late lower gastrointestinal toxicities, and the point estimate for IMRT-CCRT was expected to be <8%, which was half of that in the observational study using 3DCRT-CCRT 1 . The trial has been registered in the Japan Registry of Clinical Trials (identifier: jRCTs031180194). Results: Between April 2017 and May 2021, 220 patients from 45 institutions were enrolled. The median age was 44 (range 23-70) years. Regarding histological distribution, 163 patients (74%) had squamous cell carcinoma, 40 (18%) had adenocarcinoma, and 17 (8%) had adenosquamous carcinoma. Pathological examination showed positive pelvic lymph nodes in 183 patients (83%) and parametrial invasion in 92 (42%). The median number of positive lymph nodes was one (range 0-19). The 3-year RFS was 79.9% (90% CI: 75.0%-83.9%). The proportion of ≥grade 3 late lower gastrointestinal toxicities was 6.0% (13/216). The 3-year overall survival and locoregional RFS were 91.3% (95% CI: 86.7%-94.4%) and 87.7% (82.5%-91.4%), respectively. Conclusion: This prospective trial confirmed that IMRT-CCRT with weekly cisplatin (40 mg/m²) provides non-inferior oncologic outcomes and reduces late lower gastrointestinal adverse events compared to 3DCRT-CCRT in patients with high risk postoperative cervical cancer.

Keywords: cervical cancer, IMRT, postopeartive

References: 1. Isohashi F, et al. Int J Clin Oncol. 2019; 24(5): 575-582