ESTRO 2023 - Abstract Book

S1123

Digital Posters

ESTRO 2023

PO-1393 Can short radiotherapy be effective in treating locally advanced rectal cancer?

S. Ghorbel 1 , R. Moujahed 2 , M. Ben Rejeb 3 , M. Mezghani 1 , A. Hamdoun 1 , L. Kochbati 4

1 Abderrahmen Mami Hospital, radiation oncology, ariana, Tunisia; 2 Abderrahmen Mami Hospital, radiation oncolgy, ariana, Tunisia; 3 Abderrahmen Mami Hospital, radiation oncology , ariana, Tunisia; 4 Abderrahmen Mami Hospital, radiation oncolgy , ariana, Tunisia Purpose or Objective The purpose of this study was to evaluate early outcomes of short course preoperative radiotherapy (SRT) followed or not by consolidation chemotherapy (CC) in locally advanced rectal cancer (RC) in term of pathological response. Materials and Methods In this prospective study, patients with RC with high risk features for relapse were allocated to three different RT-courses. SRT and surgery within one week, SRT-delayed surgery after 4-8 weeks or SRT followed by CC and surgery after 2-4weeks. Chemotherapy (CT) consisted of six cycles of CAPOX or nine cycles of FOLFOX. Surgery was done according to total mesorectal excision principles. Pathological assessment for tumor regression of the resected sample was done according to Dworak grading system. Using IBM SPSS Statistics (version 25.0), we compared proportions using the χ 2 test and continuous data, depending on the distribution, with Student’s t test or the Mann-Whitney U test. Results 50 patients met our inclusion criteria. Mean age was 63 years old. Most of tumors were located in the middle rectum (56%). All patients received 3D-conformal SRT (25 Gy in 5 fractions). 15 (30%) patients had surgery within one week after completing RT. 14 (28%) patients had surgery after a delay 4-8 weeks. 21 patients (42%) received CC, 71% of these patients received FOLFOX CT , the other 29% received CAPOX. Toxicity related to CC was acceptable and it was interrupted only in one case due to digestive toxicity. In the group of patients who received CC, complete response was seen in 4 cases (19%), a partial response was seen in 14 patients (66% ) and a progression of the disease in 3 cases (14%). Complete response (CR) was confirmed in two patients, for whom a 'watch and wait' strategy was recommended. The anatomopathological study of the surgical specimen showed a complete pathological response (pCR) rate of 13% in all specimens studied. pCR was seen in 1 patient (7%) after SRT, 1 (7%) in SRT-delayed surgery group and 4 (25%) in SRT-CC group. A statistically significant association between PTV volume and pCR (p=0.03) was shown. A large predictive volume was more often associated with tumor remnant. CC was associated with higher rates of tumor downstaging (0.006), fewer positive nodes on lymph node dissection (p=0.021), and absence of vascular invasion (p=0.037) and perineural sheathing (p=0.037). These associations were not correlated with the type of CT or the number of cycles administered. Analysis of pathological response according to the time to surgery had not shown a statistically significant association in the three subgroups. Conclusion Our results are consistent with the literature. Total neoadjuvant treatment including CC improves pathological outcomes in patients treated with short course radiotherapy without adding significant toxicity. 1 Chonnam National University Medical School, Radiation Oncology, Hwasun-eup, Korea Republic of; 2 Chonnam National University Medical School,, Radiation Oncology, Hwasun-eup, Korea Republic of; 3 Chonnam National University Medical School, Radiation Oncology, Hwasun-eup, Korea Republic of; 4 Chonnam National University Medical School, Radiation oncology, Hwasun-eup, Korea Republic of Purpose or Objective To evaluate the role of hypofractionated preoperative chemoradiotherapy (CRT) with oral capecitabine in rectal cancer patients Materials and Methods A total of 76 patients with rectal cancer who received surgery after preoperative CRT were analyzed. Number of patients with stage I, II, III, and IVa were 5, 29, 36, and 6, respectively. Distal extent of tumor of ≤ 5 cm from anal verge (AV) and > 5cm were in 31 and 45 patients, respectively. Preoperative CRT was delivered by either schedule such as 35 Gy in 10 fractions to primary tumor simultaneously boosted and 33 Gy to remaining pelvis, or 33 Gy to whole pelvis according to the patient’s performance or tumor stage. Delayed surgery was performed after the completion of CRT. Oral capecitabine was administered at a dose of 1650 mg/m2 /day during radiotherapy concurrently. Tumor response, toxicity, and survival were the study endpoints. Results Nine patients (11.8%) achieved pathologically complete response. Sphincter saving was achieved in 23 /31 (74.2%) patients ≤ 5cm from AV and 45 /45 (100%) of >5cm. Of the 76 patients, 29 (38.2%) achieved T-downstaging and 25 (61.0%) had N- PO-1394 The role of hypofractionated preoperative chemoradiotherapy in rectal cancer patients T. Nam 1 , I.J. Cho 1 , J. Jeong 2 , Y. Kim 3 , J. Song 4 , S. Ahn 1 , M.S. Yoon 1 , S.H. Cho 1