S696
Clinical – Lower GI
ESTRO 2026
rectum, with clinical T3–4 and/or N+ staging, who underwent total neoadjuvant therapy (TNT) consisting of chemoradiotherapy (CRT) followed by consolidation chemotherapy were included. Patients were treated according to two RT dose protocols at two tertiary referral cancer centers between January 1, 2018, and March 31, 2025. Pathological response was assessed using the 8th edition TNM staging system and the Modified Ryan Tumor Regression Grade (TRG) classification. Pathological complete response (pCR) was defined as ypT0N0 and TRG0. Near-complete response was defined as TRG1. Clinical complete response (cCR) was assessed by magnetic resonance imaging and colonoscopy. Endpoints were clinical/pathological response rates and toxicity. Results: In the high-dose (HD) group, 21 patients were treated with 60 Gy in 25 fractions to the primary tumor with a 7 mm clinical target volume (CTV) margin and to pathological lymphadenopathies with a 5 mm CTV margin, with a planning target volume margin of 5 mm. The mesorectum and pelvic lymphatics were treated with 45 Gy in 25 fractions. In the standard- dose (SD) group, 41 patients received 45–50.4 Gy in 25–28 fractions, administered homogeneously to the pelvic lymphatics, primary tumor, and mesorectum. Baseline sociodemographic, clinicopathological, and treatment characteristics were comparable between the two groups (Table 1). The HD RT group demonstrated significantly higher response rates than the SD group, including higher rates of pCR (47.1% vs. 17.9%; p=0.046), combined pCR or near-complete response (64.7% vs. 35.9%; p=0.046), combined cCR and/or pCR (57.1% vs. 22.0%; p=0.006), and tumor downstaging (81.0% vs. 53.7%; p=0.035). Multivariate analysis revealed a significant association between RT dose and pCR (p=0.029). Pathological near-complete or complete response was significantly correlated with gender (p=0.019), Eastern Cooperative Oncology Group (ECOG) performance status (p=0.024), clinical N stage (p=0.046), and RT dose (p=0.032). Combined cCR and/or pCR was associated with extramural venous invasion (p=0.039) and RT dose (p=0.013) (Table 2). There were no statistically significant differences between the SD and HD groups regarding grade 3–4 acute (p=0.362) or late (p=0.246) adverse events, nor in early (p=0.739) or late (p=0.773) postoperative complications.
trials are needed to obtain conclusive data. References: 1. DOI: 10.31557/APJCP.2021.22.5.1607 2. DOI: 10.3390/cancers152357023. DOI: 10.1007/s00066-014- 0650-04. DOI: 10.1016/j.radonc.2018.11.0235. DOI: 10.1016/j.radonc.2014.08.0356. DOI: 10.1016/j.clon.2020.06.0087. DOI:10.1007/s00384-013- 1772-z Keywords: rectal cancer, radiotherapy dose escalation, pCR Radiotherapy dose escalation in total neoadjuvant therapy for rectal cancer: A safe path to enhanced pathological response Yasin Ozyurek 1 , Havva Beyaz 2,3 , Pervin Hurmuz 1 , Mutlu Hayran 4 , Ibrahim Ethem Gecim 5 , Erdal Birol Bostanci 6 , Omer Dizdar 4 , Deniz Akata 7 , Pinar Ozgen Kiratli 8 , Cenk Sokmensuer 9 , Timucin Erol 10 , Ipek Pinar Aral 2,3 , Tuba Dilay Kokenek Unal 11,12 , Burak Bilgin 13,14 , Yilmaz Tezcan 2,3 , Ferah Yildiz 1 1 Department of Radiation Oncology, Hacettepe University, Faculty of Medicine, Ankara, Turkey. 2 Department of Radiation Oncology, Ankara Yıldırım Beyazıt University, Faculty of Medicine, Ankara, Turkey. 3 Department of Radiation Oncology, Ankara Bilkent City Hospital, Ankara, Turkey. 4 Department of Digital Poster 1306 Preventive Oncology, Hacettepe University, Faculty of Medicine, Ankara, Turkey. 5 Department of General Surgery, Ankara University, Faculty of Medicine, Ankara, Turkey. 6 Department of General Surgery, Ankara Bilkent City Hospital, Ankara, Turkey. 7 Department of Radiology, Hacettepe University, Faculty of Medicine, Ankara, Turkey. 8 Department of Nuclear Medicine, Hacettepe University, Faculty of Medicine, Ankara, Turkey. 9 Department of Pathology, Hacettepe University, Faculty of Medicine, Ankara, Turkey. 10 Department of General Surgery, Hacettepe University, Faculty of Medicine, Ankara, Turkey. 11 Department of Pathology, Ankara Yıldırım Beyazıt University, Faculty of Medicine, Ankara, Turkey. 12 Department of Pathology, Ankara Bilkent City Hospital, Ankara, Turkey. 13 Department of Medical Oncology, Ankara Yıldırım Beyazıt University, Faculty of Medicine, Ankara, Turkey. 14 Department of Medical Oncology, Ankara Bilkent City Hospital, Ankara, Turkey Purpose/Objective: This study aimed to investigate the impact of neoadjuvant radiotherapy (RT) dose escalation on treatment response in patients with locally advanced rectal cancer (LARC). Material/Methods: A total of 62 patients diagnosed with rectal adenocarcinoma located in the distal to middle
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