S685
Clinical – Lower GI
ESTRO 2026
Digital Poster Highlight 638 Total Neoadjuvant Therapy Using VMAT - SIB With Consolidation Chemotherapy Improves Complete Response in Low - Lying Rectal Cancer Reza Ghalehtaki 1,2 , Sheyda Pashapour-Khoyi 1 , Romina Abyaneh 2 , Kasra Kolahdouzan 1 , Afsaneh Maddah- Safaei 1 , Ebrahim Esmati 1 , Nima Mousavi-Darzikolaei 1 , Farshid Farhan 1 , Mohammad Babaei 1,2 1 Radiation Oncology, Tehran University of Medical Sciences, Tehran, Iran, Islamic Republic of. 2 Radiation Oncology Research Center, Cancer Research Institute, Tehran, Iran, Islamic Republic of Purpose/Objective: To determine if a total neoadjuvant therapy (TNT) regimen incorporating volume modulated arc therapy (VMAT) with a simultaneous integrated boost (SIB) and consolidation chemotherapy significantly improves the complete response (CR) rate in low-lying rectal cancer. Material/Methods: This is a single-arm, phase II clinical trial (IRCT20150929024266N6) on patients with newly diagnosed, low-lying rectal adenocarcinoma (T2-4 N0-2 M0 at ≤ 5 cm from anal verge). The experimental arm received VMAT-SIB (55-60 Gy/25 fractions in 5weeks) plus concurrent capecitabine 825 mg/m ² BD, followed by 6 cycles of consolidation CAPOX or FOLFOX. Clinical complete response was defined as the absence of ulcer or mass or polyp at the site of previous tumor in endoscopy and mrTRG1-2 in restaging MRI. Patients with cCR had the option to undergo non-operative management, while resection was mandatory for those without cCR. Enrolled patients were matched with a historical control group of low-lying rectal cancer patients based on age, sex, and clinical T/N stage undergoing capecitabine-based conventional 3DRT (50-50.4 Gy) followed by surgery and adjuvant chemotherapy. The primary endpoint was the complete response (CR) rate, consisting of either a cCR or pathological complete response (pCR). Results: A total of 30 patients have been recruited so far (Table 1). At the time of this analysis, 20 patients who had completed the entire treatment protocol of VMAT-SIB TNT were compared to the 20 best-matched patients. In the VMAT-SIB TNT group, 12 patients (60%) achieved a cCR who subsequently entered a W&W program. Of the remaining 8 patients, 7 underwent surgery (1 LAR and 6 APR), and one patient without a cCR refused surgery. As shown in Figure 1, the CR rate was 75% in the VMAT-SIB TNT group (15/20: 3 pCR and 12 cCR) compared to 15% (3/20, all pCR) in the control group (p < 0.001). No significant difference was observed in sphincter preservation rates between the VMAT-SIB TNT (65%, 13/20: 12 cCR cases and 1 LAR) and the control (75%, 15/20: all LAR cases) groups (p = 0.49).
Conclusion: There is marked heterogeneity in liver re-irradiation practice, and its systematic implementation remains limited. Prospective studies are needed to determine optimal patient selection criteria, dose constraints, and evidence-based best practices for liver re- irradiation. References: Andratschke N, et al. Lancet Oncol. 2022. doi:10.1016/S1470-2045(22)00447-8Gkika E et al. Strahlenther Onkel. 2019. doi: 10.1007/s00066-018- 1385-0Kimura T, et al. Int J Radiat Oncol Biol Phys. 2020. doi: 10.1016/j.ijrobp.2020.07.034 Mohamed Yoosuf AB, et al. Cureus. 2023. doi: 10.7759/cureus.39600 Barsky AR, et al. J Gastrointest Oncol. 2020. doi: 10.21037/jgo.2019.09.03. Tomizawa K, et al. Int J Radiat Oncol Biol Phys. 2023. doi: 10.1016/j.ijrobp.2023.02.036 Owen D, et al. Semin Radiat Oncol. 2020. doi:
10.1016/j.semradonc.2020.02.004 Keywords: reirradiation, liver, survey
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