ESTRO 2021 Abstract Book

S1047

ESTRO 2021

We have developed the CLICAL algorithm for predicting the benefit of SBRT for metastases from colorectal cancer. CLICAL might be used as a screening tool for SBRT referrals to facilitate decisions on the electivity of each case to enter the SBRT program.

PO-1269 C-Reactive Protein as predictive factor for response to chemoradiotherapy in Rectal Cancer F.A. Lima Aires 1 , E.D. Rodrigues Pinto 1 , M. Reis Lima Marques 1 , M.G. Pinto 2 1 Centro Hospitalar Universitário São João, Radioncology, Porto, Portugal; 2 Centro Hospitalar Univeristário São João, Radioncology, Porto, Portugal Purpose or Objective The standard of care for locally advanced rectal cancer is neoadjuvant chemoradiotherapy followed by surgery. This study aims to identify predictive factors for tumor response. Materials and Methods All patients with stage I, II and III rectal adenocarcinoma, who underwent neoadjuvant long course radio- chemotherapy (nCRT) from January 2013 to December 2019 were identified. Serum measurements of Hemoglobin, C-Reactive Protein (CRP), platelets, ratio neutrophils/lymphocytes, CEA and CA 19.9 were obtained before nCRT. The Ryan´s Tumor Regression Grade Scoring System measured the pathologic tumor regression. For the comparison of the groups calculated by the threshold predictors value, the Chi-square test and the Fisher’s exact test were used. Logistic regression was performed to determine univariate relationships between preoperative clinical predictors and response to nCRT. Multivariate logistic regression analysis, including all statistically significant covariates at a p value of 0.05 or lower, was performed by a stepwise backward procedure to derive a final model of the variables that had a statistically significant relationship between response and nCRT. Results The study included 171 patients. Most of the patients were male (n=108, 63.2%), the median age of the studied cohort was 62 years (std. deviation 12 years) and the ECOG 0 was predominant, 80.7% (n=138). At initial presentation and radiologic examination, most of the patients had cT3 disease (n=121, 70.3%) and 79.5% (n=136) were node (cN) positive. Radiotherapy treatment dose varied between 45-55 Gy with three- dimensional conformal radiation therapy technique on 86% (n=147) and intensity-modulated radiation therapy on 14.0% (n=24). During the neoadjuvant treatment course 7.6% (n=13) of patients developed a complete clinical response (cT0), 19.3% (n=33) developed complete pathologic response (pT0, Ryan0), 32.7% (n=56) of patient’s moderate response (Ryan1). These patients were classified as responders, 60.6% (n=56). No responders group included Ryan 2 to 3, 37.4 % (n=64), and unresectable tumors, 2.9% (n=5). Responders to nCRT were significantly associated with clinical T-stage of 2-3 (p=0.035), a CRP 3.5 or lower (p<0.001) and a CEA 2.6 or lower (p=0.013). There was no association between responders and gender, ECOG, cN, tumor localization, chemotherapy capecitabine, RT technique, hemoglobin, platelets, NRL and CA 19.9. In cases where there was evidence of possible interaction (interaction term p<0.20), a logistic regression model using prognostic preoperative factors identified PCR 3.5 or lower (OR 0.055; 95% CI 0.011–0.276; P<0.001) as strong independent predictor of response to treatment.