ESTRO 2024 - Abstract Book

S1528

Clinical - Lower GI

ESTRO 2024

From 2012 to 2022, patients with LARC were retrospectively analyzed. Radiotherapy was performed with a total dose of 45 Gy, 1,80 Gy/day, to the pelvic nodes and a simultaneous integrated boost (total dose 55 Gy, 2,20 Gy/day) to mesorectum. Capecitabine was administered concomitantly twice a day for 5 days/week. Toxicities were recorded by the RTOG/EORTC scale. Pathological Complete Response (pCR) was evaluated according to Mandard tumor regression grade (TRG) and the population was divided in 2 groups: TRG 1-2 and TRG 3-4-5. The Kaplan Meier method was used to calculate the 5- and 10-year rates of OS, DFS and LC. OS was defined as the time interval between surgery and death; DFS curve, as the time between surgery and the first verified event and LC as the time between surgery and the locoregional recurrence. For patients in whom none of the events occurred, the observational time interval was defined as the period from surgery to the last follow-up visit. The Kaplan-Meier method was used to estimate differences between the 2 TRG groups, as well. A P-value less than 0.05 was considered statistically significant. In this study, 178 patients were analyzed, with a median follow-up of 42 months. The median patient age was 68 years and 121 patients were male. Most patients (86%) had cT3 tumors. Lower gastrointestinal toxicity was the most frequent acute side effect: 120 patients had grade 1-2 toxicity, whereas only 2 patients experienced severe toxicity. Grade 1-2 skin toxicity was reported in 45 patients and grade-3 in 2 patients. There were reported no other severe toxicities. 168 patients underwent surgery and anterior resection was performed in 106 patients (59%), followed by Transanal Endoscopic Microsurgery in 20 (12%). Among late toxicities, bowel dysfunction (G3 toxicity) was reported in 6 patients (3%). No other severe late toxicities were recorded. The 5-year OS, DFS and LC rates were 88%, 80% and 98%, respectively. Long-term results at 10 years showed OS, DFS and LC rates of 82%, 75%, and 98%, respectively. Looking at the classification of patients according to TRG, we observed that 107 (64%) patients showed TRG 1-2 and 62 (36%) patients, TRG 3-5. Results:

Figure 1 shows that patients with TRG1-2 had better OS, with 5- and 10-year rates of 89% and 89% (compared with 86% and 67%, for patients with TRG3-5, respectively), and a better LC with the 5- and 10-year LC rates for TRG1-2 patients of 89% and 89% (versus 86% and 67%, respectively, for patients with TRG3-5). Regarding DFS, as shown in Figure 2, patients with TRG1-2 showed 5- and 10-year rates of 82% and 81% compared with 60% and 40%, for patients with TRG3-5, respectively.