ESTRO 2025 - Abstract Book

S1216

Clinical – Lower GI

ESTRO 2025

National Clinical Research Center for Cancer / Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China

Purpose/Objective: To analyse the long-term efficacy of simultaneous integrated boost (SIB) intensity-modulated radiation therapy (IMRT) for locally advanced rectal cancer. Material/Methods: This was a randomized controlled phase II study (NCT02195141). Patients with histological confirmed, newly diagnosed, locally advanced rectal adenocarcinoma (cT3-T4/N+) located within 10 cm from the anal verge were randomly allocated to preoperative SIB-CRT group or CRT group. In CRT group, patients received 50Gy in 25 fractions pelvic IMRT and concurrent capecitabine (825 mg/m2 bid d1-5 weekly). Patients in SIB-CRT group received 50 Gy pelvic IMRT and a simultaneous integrated boost of 6Gy to the primary gross tumor in 25 fractions, concurrent with the same capecitabine scheme. Radical surgery was scheduled 6-8 weeks after chemoradiation in both groups. The primary end point was pathology complete response (pCR), the second end point was DFS, OS and toxicities. Results: A total of 106 patients were enrolled between August 2013 and February 2015, of which 55 and 51 patients were assigned to the SIB-CRT and CRT groups, respectively. The median follow-up time of was 9.7 years (range, 0.3-11.1 years). Thirty-seven percent of patients were ≥60 years (median age 55 years. Range 23-75 years). The majority of patients had cT3-4 (99.1%) and cN+ (87.7%) disease. The baseline characteristics were generally balanced between two groups (Table 1). The acute toxicities of chemoradiotherapy were generally mild and similar between groups. Eighty-two patients received surgical resection. The pCR and CR rates in the SIB-CRT and CRT groups were comparable with no significantly difference (pCR:15.6% vs. 18.9%, P =0.69; CR:20.0% vs. 19.6%, P =0.96). However, SIB-CRT was correlated with long-term survival benefits, the 9-years DFS of SIB group and IMRT group were 70.8% vs. 47.2%( P =0.014), respectively. SIB-CRT also significantly improved 9-years OS: 74.3% vs. 48.9%( P =0.008). The detailed long-term secondary outcomes are in Table 2. After a median follow-up of 3 years, we collected the late bowel complications in patients undergoing surgery. The grade 1-2 complications did not differ between groups (20.6% vs. 37.0%, P >0.05) and no grade 3 complications were observed, with proctitis (G=2), the only grade 2 complication, was observed in 5 out of 61 responded patients.