ESTRO 2022 - Abstract Book

S1117

Abstract book

ESTRO 2022

PO-1322 NAR Score validation in TNT (Total Neoadjuvant treatment) for locally advanced rectal cancer

I.D. PERROT ROSENBERG 1,2 , J.A. Solís Campos 1,2 , G. Lazcano Alvarez 1 , G. Veillon Contreras 1,2 , B. Tudela Staub 2,1 , J. Olivares Gonzalez 1 1 Universidad de Valparaiso, Radiotherapy, Valparaiso, Chile; 2 Hospital Carlos Van Buren, Radiation Oncology, Valparaiso, Chile Purpose or Objective A current management for locally advanced rectal cancer is neoadjuvant radio – chemotherapy and total neoadjuvant treatment (TNT) is one possible approach. The purpose of this study is to analyze the oncological outcomes in survival and the impact of pathologic response in TNT using the NAR Score Materials and Methods We performed a retrospective cohort study including all locally advanced rectal cancer patients treated with TNT with a curative intention between 2017-2019, receiving 25 Gy in 5 Gy daily fractions followed by FOLFOX Chemotherapy and surgery. Pre-operative and post-operative biopsies were analyzed calculating NAR score for each patient. Survival analysis was performed using the Kaplan Meier method. The study was approved by the local ethics committee. 49 patients were identified. 4 patients cT2 (8.2%); 34 cT3 (69.4%) and 11 cT4 (22.4%). All patients completed radiotherapy with a 7-day median duration (ICR 5-7). 98% received at least 1 cycle of chemotherapy, median of 3 cycles (ICR 3-4). Median interval between radiotherapy and surgery 115 days (ICR 99-144). 6 patients (10%) operated within 12 weeks. 34 surgical biopsies were retrieved. 10 patients ypT0 (29.4%); 3 ypT1 (8.8%); 7 ypT2 (20.6%); 11 ypT3 (32.4%); 3 ypT4 (8.8%); 27 ypN0 (79.4%); 4 ypN1 (11.8%) and 3 ypN2 (8.8%). 9 patients showed pathologic complete response (18.4%). Cohort Overall Survival 75.5% within a 32 month follow up period. Median NAR score was 8.4. Considering response to TNT patients with low NAR (<8.4) had 100% Overall survival, while high NAR patients (>8.4) showed 60% overall survival. (p=0.002). Conclusion In conclusion, our TNT results are comparable to the ones found in the international literature. Although initially validated in extended concomitant neo adjuvant radio chemotherapy trials, we demonstrated NAR score still shows prognostic significance in the context of TNT. Results A. Verrijssen 1 , C. Huibregtse Bimmel-Nagel 1 , J. Cnossen 1 , J. Theuws 1 , H. Peulen 1 , H. van den Berg 1 , D. Rijkaart 1 , E. Voogt 2 , P. Burger 2 , H. Rutten 2,3 , W. Dries 1 1 Catharina Hospital, Radiotherapy, Eindhoven, The Netherlands; 2 Catharina Hospital, Surgery, Eindhoven, The Netherlands; 3 GROW School for Oncology and Developmental Biology, Maastricht University, Surgery, Maastricht, The Netherlands Purpose or Objective Intraoperative radiotherapy (IORT) has been used as a tool to provide a high dose radiation boost to a limited volume in patients with locally advanced or recurrent rectal carcinoma who have fixed tumors with a likelihood of microscopically involved resection margins, in order to improve local control. The two main techniques to deliver IORT are through High Dose Rate (HDR) Brachytherapy, termed Intraoperative Brachytherapy (IOBT), and through electrons, termed Intraoperative Electron Radiotherapy (IOERT), both having very different dose distributions. A recent paper described an improved local recurrence-free survival favoring IOBT over IOERT for patients with locally advanced or recurrent rectal cancer and microscopically irradical resections. Although several factors may have contributed to this result, an important difference between the two techniques is the higher surface dose delivered by IOBT. This article describes an adaptation of the IOERT technique at the Catharina Cancer Institute (CCI) (Eindhoven, NL) to achieve a comparable surface dose as the dose delivered by IOBT. PO-1323 Narrowing the difference in dose delivery for IOERT and IOBT for rectal cancer