ESTRO 2020 Abstract Book

S581 ESTRO 2020

Results A total of 171 MRI scans in eight patients were performed with regard to morphological and functional changes of the tumor tissue during RCT. In four patients, there was a complete pathological remission (pCR), while the other four patients achieved a partial remission (pPR) after neoadjuvant RCT and surgical resection. Volumetry based on T2- and diffusion-weighted imaging was statistically significant in terms of treatment response, and volumetric thresholds at week two and week four during RCT were defined for the prediction of pCR. In contrast, the average tumor ADC values widely overlapped between both response groups during neoadjuvant RCT and appeared inadequate to predict treatment response in this cohort. Conclusion This prospective study supports the hypothesis that some MR biomarkers can predict a pCR of rectal cancer during neoadjuvant RCT. Our data provide a useful template to tailor future MR-guided adaptive treatment concepts. PO-1100 Impact of neutrophil-lymphocyte ratio on the response of chemoradiation therapy of rectal cancer J.H. Lee 1 , J.H. Lee 1 , S.H. Kim 1 , H.C. Lee 1 1 The Catholic University of Korea, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective Preoperative chemoradiation therapy (CRT) and total mesorectal excision have been the standard care of the patients with locally advanced rectal cancer. Response to the preop CRT varied from patient to patient, approximately 10-15% of the patients achieved complete response, on the contrary, nearly 40% of the patients still showed ypT4 disease after preoperative CRT. The aim of this study is to assess the prognostic value of NLR and suggest the optimal cut-off value to predict tumor response to the preoperative chemoradiation therapy in the patients with locally advanced rectal cancer. Material and Methods We analyzed the medical records of 1134 patients who diagnosed with locally advanced rectal cancer and treated with neoadjuvant CRT followed by radical surgery at St. Vincent hospital, Seoul St. Mary’s hospital, Chonnam National University Hwasun Hospital, Gyeongsang National University Hospital and Dongsan Medical Center from 1998 to 2015. All patients had histologically confirmed rectal adenocarcinoma within 10 cm from anal verge. All patients received preoperative CRT to the pelvis followed by TME. Complete blood count (CBC) was performed at initial workup before treatment and NLR was calculated with differential count Results Optimal cut-off values of the NLR was revealed as 1.98. the NLR showed average value for predicting death (AUC 0.516, 95% CI 0.471-0.561, p<0.001). the sensitivity and specificity were 54.2% and 54.1% respectively. According to the cut-off value, patients were divided into two groups; high NLR (NLR≥2.0, n=530) and low NLR (NLR<2.0, n=604). The patients with low NLR achieved pathologic complete response more frequently. 105 patients of total 604 patients (17.4%) with low NLR showed no remnant tumor cells, compared to 63 patients of the 530 patients (11.9%) with high NLR did (p=0.012). The proportion of the patients who were downstaged to T1-2N0 was evaluated. In the low NLR group, 258 patients (42.7%) were downstaged, while 199 patients (37.5%) in the high NLR group were, which showed a tendency but did not reach statistical significance (p=0.087). Conclusion In this large-scale multi-center analysis, NLR was once again identified as a predictor of treatment response of preop CRT in patients with locally advanced rectal cancer.

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).

Conclusion We recorded mild urinary toxicity for patients with rectal adenocarcinoma treated with IMRT concomitant with capecitabine. We found no correlation between the dose to the whole bladder and cystitis. We need further investigation to achieve the optimal cut-off value for dose to the bladder in correlation with cystitis in order to optimize future IMRT plans for patients with rectal adenocarcinoma. PO-1099 Response prediction by daily fractional MRI during neoadjuvant radiochemotherapy in rectal cancer T. Bostel 1,2 , C. Dreher 3,4 , D. Wollschläger 5 , A. Mayer 1 , S. Bickelhaupt 6 , H. Schlemmer 4 , P. Huber 2,7 , F. Sterzing 8 , J. Debus 2,7 , N. Nicolay 2,9 1 University Medical Center Mainz, Radiation Oncology, Mainz, Germany ; 2 German Cancer Research Center DKFZ, Clinical Cooperation Unit Radiation Oncology, Heidelberg, Germany ; 3 Mannheim University Hospital, Radiation Oncology, Mannheim, Germany ; 4 German Cancer Research Center DKFZ, Division of Radiology, Heidelberg, Germany ; 5 University Medical Center Mainz, Institute of Medical Biostatistics- Epidemiology and Informatics IMBEI, Mainz, Germany ; 6 German Cancer Research Center DKFZ, Division of Medical Imaging and Radiology – Cancer Prevention, Heidelberg, Germany ; 7 Heidelberg University Hospital, Radiation Oncology, Heidelberg, Germany ; 8 Kempten Clinic, Radiation Oncology, Kempten, Germany ; 9 Medical Center - University of Freiburg, Radiation Oncology-, Freiburg, Germany Purpose or Objective Only few data are available on MR imaging during neoadjuvant treatment of rectal carcinomas, that may help to devise adaptive radiotherapy (RT) concepts. This study aimed at prospectively evaluating daily fractional MRI during neoadjuvant radiochemotherapy (RCT) to analyze the predictive value of MR biomarkers for Locally advanced rectal cancer patients were examined with daily MRI during neoadjuvant RCT. Tumor delineation was performed on each MRI scan based on T2 and DWI sequences. The daily apparent-diffusion coefficient (ADC) was calculated. Volumetric and functional tumor changes during RCT were analyzed and correlated with the pathological response after surgical resection. treatment response. Material and Methods