ESTRO 2020 Abstract book

S628 ESTRO 2020

difference on LRFS (94.0%, 93.4%, and 99.2%, respectively, p=0.20). However, when we divided patients by risk factors, in patients with anal verge ≤5 cm or DRM ≤2 cm, the 5-year LRFS was significantly better with CCRT (98.9% vs 87.4%, p=0.006). In contrast, in the patients with no risk factor, 5-year LRFS was not significantly affected by adding CCRT (100% with CCRT vs 99.0% without CCRT, p=0.66). Conclusion Even if patients had pathologic T3N0 rectal cancer with negative CRM, LRFS was significantly better with postoperative CCRT in patients with risk factors like anal verge ≤5 cm and DRM ≤2 cm. Postoperative CCRT should be recommended in these patients. PO-1098 Dosimetric correlation of acute urinary toxicity in patients with rectal cancer treated with IMRT A. Secerov Ermenc 1 , J. But Hadzic 1 1 Institute of Oncology Ljubljana, Department of Radiation Oncology, Ljubljana, Slovenia Purpose or Objective Preoperative chemoradiation followed by surgery is the standard care for patients with locally advanced rectal cancer. The implementation of intensity modulated radiotherapy (IMRT) resulted in reducing the acute side effect during treatment, however they may still cause patient discomfort. We dosimetrically analyzed IMRT plans in locally advanced rectal cancer patients and correlated them with acute urinary toxicity. Material and Methods We analyzed the data from patients with rectal cancer who were included in a prospective phase II study at our institution. From January 2014 till March 2015 we treated 51 patients with operable stage II-III rectal adenocarcinoma, they received preoperative IMRT with pelvic dose of 41.8 Gy and simultaneously delivered 46.2 Gy toT2/3 and 48,4 Gy to T4 tumors in 22 fractions, concomitant with capecitabine 825mg/m2/12 hours weekends included. Patients were weekly evaluated to assess acute toxicity. Toxic side effects were assessed according to the Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. We calculated the mean dose (D mean ) to the whole bladder and the relative and absolute volume of the bladder that received 10 Gy (V 10Gy ), 20 Gy (V 20Gy ), 30 Gy (V 30Gy ), 35 Gy (V 35Gy ) and 40 Gy (V 40Gy ), respectively. Student's t -test was used for correlating the doses received by the bladder with the grade of acute toxicity. Results Forty-eight patients with rectal cancer were available for analysis. No urinary discomfort was experienced by 27 (56.3%), grade 1 cystitis by 19 (39,6%) and grade 2 by 2 (4,2%) patients, respectively. We found no statistically significant correlation between D mean , relative and absolute V 10Gy , V 20Gy , V 30Gy , V 35Gy , V 40Gy and the grade of acute toxicity (Table 1).

cancer (LARC) and devise the nomogram based on the results. Material and Methods We retrospectively analyzed 514 stage II and III patients treated with preoperative CRT between January 2004 and May 2019. The radiation dose was 45 Gy, followed by a primary tumor boost of 5.4 Gy. Oral capecitabine was given to 393 patients (76.5%) and infusional 5- fluorouracil/leucovorin to 115 patients (22.4%). Pathological responses were assessed according to the Dworak tumor regression grade (TRG) system. Patients were categorized as having a good response (TRG 3/4, n = 184) or a poor response (TRG 1/2, n = 330). Results The good response group tended to have following pretreatment clinical characteristics; a low clinical T/N stage, small primary tumor and metastatic lymph node diameter, shallow extramural tumor depth in MR image, high hemoglobin (Hb), low carcinoembryonic antigen (CEA) and a long interval (≥6 weeks) between radiotherapy and surgery compared to the poor response group. A multivariate logistic regression analysis found that the predictors of good response were small tumor size (OR = 0.79; P = 0.016), extramural tumor depth less than 3 mm (OR = 1.81; P =0.006), age more than 45 years (OR = 2.85; P = 0.015), high level of Hb more than 15 g/dl (OR = 1.98; P = 0.006), interval between CRT and surgery more than 6 weeks (OR = 2.65; P = 0.043), and low level of CEA (1 ng/ml < CEA ≤ 3 ng/ml; OR = 1.83; P = 0.015, CEA ≤ 1ng/ml; OR = 4.02; P = <0.001). The predictive nomogram was developed and rendered area under the curve (AUC) of 0.720. Conclusion Pretreatment CEA/Hb levels, tumor size, extramural tumor depth, age, and CRT to surgery interval were independent predictors for good pathologic tumor response after preoperative CRT for LARC. Patients with these clinical factors could be considered for candidates of organ preservation policy by intensifying chemoradiotherapy. PO-1097 Who needs postoperative CCRT in patients with pT3N0 rectal cancer with negative resection margin? J.Y. Baek 1 , Y. Jeong Il 1 , P. Hee Chul 1 , C. Doo Ho 1 , Y. Gyu Sang 1 , C. Won Kyung 1 1 Samsung Medical Center, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective This study was performed to identify risk factors of local recurrence (LR) and find who can benefit from postoperative chemoradiotherapy (CCRT) in pathologic T3N0 rectal cancer with negative circumferential We retrospectively reviewed data on 365 patients who had pathologic T3N0 rectal cancer from January 2003 to December 2012 in the Samsung Medical Center. All patients received upfront surgery without preoperative radiotherapy and postoperative management was no adjuvant therapy, chemotherapy alone, or concurrent chemoradiotherapy (CCRT). Patients who had positive CRM or no data on CRM were excluded. Results The median follow up period after surgery was 71 months (range, 3 - 177 months). The estimated 5-year overall survival, disease-free survival, LR-free survival (LRFS) was 95.9%, 86.9%, and 96.3%, respectively. On multivariate analysis, distance from anal verge ≤5 cm, distal resection margin (DRM) ≤2 cm, the number of examined lymph nodes ≤12, and CCRT (-) was found to be significant poor prognostic factors for LRFS. When we compared three groups: surgery alone (n=122), chemotherapy alone (n=100), and CCRT (n=143), there was no significant This bstract has been withdrawn resection margin (CRM). Material and Methods

Conclusion We recorded mild urinary toxicity for patients with rectal