ESTRO 2020 Abstract Book

S580 ESTRO 2020

Purpose or Objective To evaluate how post-treatment carcinoembryonic antigen (CEA) serum concentration decrease corresponds with the outcome of definitive radiotherapy (RT) or radiochemotherapy (RT-CHT) in primary unresectable rectal cancer patients (pts). Material and Methods Inclusion criteria of this retrospective study were: primary unresectable, locally advanced rectal cancer with histopathological confirmation, RT/RT-CHT as radical treatment and measured CEA post-treatment level. Between 2000 and 2016 145 pts were treated due to unresectable rectal cancer. The aim of the treatment was tumour downsizing allowing further radical surgery. Among them, 71 had pre- and post-treatment CEA and 10 post-treatment CEA measurements, therefore the group of 81 pts (60 men, 21 women) was evaluated in this study. Out of 81 pts: 33 (41%) received RT (accelerated hyperfractionation: 66 Gy in 1.5 Gy fx, twice a day or conventional fractionation 60-66 Gy in 2 Gy fx) and 48 (59%) RT-CHT (54 Gy/1.8 Gy fx +2 cycles of 5-Fu LV). Six to eight weeks after RT or RT-CHT tumor resectability was evaluated again using physical examination and imaging studies. Pts were divided in two groups. (group A): pts with CEA post-treatment decrease or below 5 ng/ml and (group B): pts without post-treatment decrease of CEA or level above 5 ng/ml. Statistical test used were Kaplan-Meyer survival analysis, log rank test and Cox regression model. Results Median follow-up after the end of RT/ RT-CHT was 5.5 years. Fifty four pts (67%) had radical resection after neoadjuvant RT/RT-CHT and 27 (33%) were still unresectable. CEA serum concentration decrease or level below 5ng/ml (group A) was observed in 63 pts (77%), CEA serum concentration increase/level above 5ng/ml (group B) in 18 (22%). In univariate analysis pts in group A had better overall survival compared to group B (p=0.039, median OS of 40 months vs 87 months, respectively). Five-year OS was 62% in group A compared to 30% in group B. Moreover, pts who received RT-CHT had better 5-year OS compared to RT (63 vs 44%) respectively (p=0.04). Pts after radical resection had better 5-year OS than those still uresectable (71% vs 21%, p=0,000). Significant factors were then checked in multivariate analysis. Only radical surgery had reached statistical significance (p=0,000) for OS. Conclusion Pts with post-treatment serum CEA concentration decrease or level below 5 ng/ml tend to have better overall survival compared to those in whom CEA concentration did not decrease after the neoadjuvant treatment. Post-treatment decrease in serum CEA concentration in primary unresectable rectal cancer patients who received definitive RT/RT-CHT can be a useful predictor of outcome. Analysis on larger group of pts is needed to evaluate these results. PO-1096 Prediction of pathologic response by clinical characteristics following preoperative CRT in LARC 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 Abstract withdrawn

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 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 resection margin (CRM). Material and Methods