ESTRO 2020 Abstract book

S317 ESTRO 2020

LARC in terms of ypCR with tolerable toxicity, using IMRT (concomitant boost technique), resulting therapeutic gain. Material and Methods RTRC-001 (ClinicalTrials.gov Identifier: NCT02964468) is a collaborative (GICOR and SEOR) prospective multicenter randomized phase III trial testing dose escalation radiation in LARC. Patients with LARC were randomized 1:1 to either a standard treatment arm consisting in preoperative chemoradiation (45Gy in 25 fractions to the pelvis with a sequential 5,4Gy in three fractions to the gross tumour administered with 3D-conventional radiotherapy, or to experimental arm including neoadjuvant chemoradiation (2,15Gy x 25 sessions using IMRT with simultaneous integrated boost). Fluoropyrimidine-based chemotherapy regimens were administered concomitantly, surgery was performed according to TME principles in both study arms and postoperative chemotherapy was optional and could be omitted by participating institutions. Dual primary endpoints were ypCR defined as ypT0 ypN0 and acute gastrointestinal (GI) toxicity evaluated according to CTCAE.4 criteria. Secondary endpoints included disease- free survival (DFS) at 3 years, overall survival, local control, tumour regression grade using Mandard-scoring- system (TRG), toxicity profile and quality of life. Results From January 2017 to August 2019, 125 patients from 7 Spanish centers were randomized with a total of 108 patients evaluable for ypCR analysis at this time (Standard arm: 56, Experimental arm: 52). Radiation therapy dose escalation arm showed a statistically significant improvement in ypCR vs standard arm: 34,6% vs 16,4%, p = 0,03 on univariate analysis. TRG1-3 occurred in 18 patients (34,6%) in experimental arm and in 9 patients (16,4%) in standard arm (p= 0,044). Predictive factors for ypCR were identified: time to surgery > 10weeks (p=0,06) and upper rectal tumours (p=0,015) were associated to higher ypCR by univariate analysis. With a median follow- up after surgery of months 12 months (range 0–28 months). 1-year DFS rate was 90,8% for experimental arm and 88,6 % for standard arm; hazard ratio (HR) 0,69 (95% CI 0,17– 2,8), stratified log-rank p = 0,61. Acute GI toxicity grade I and II were 48,1% vs 53,6% and 23,1% vs 23,1% respectively favoring experimental arm. Acute GU toxicity grade I and II were 30,8% vs 39,3% and 1,9% vs 1,8% respectively favoring experimental arm. None developed acute GU or GI toxicity grade III or IV. Major surgical complication rates were 23,2% for standard treatment vs 15,3% for experimental arm.

Results The detection sensitivity, specificity and accuracy of the model on previously unseen data was 97%, 93% and 96% respectively. 36/39 patients had all fiducial markers correctly identified with clinically acceptable accuracy. 22/39 patients had intra-prostatic calcifications ≥ 2 mm. The mean absolute difference between the detected fiducial and ground truth CoM was 0.9 ± 0.9 mm [0 3.2].

Conclusion A deep learning method for automatic fiducial identification in MEGRE MR images was developed and evaluated, demonstrating state of the art detection metrics. The performance of the model is expected to be further improved with additional training data and we are aiming to implement it as a clinical decision support software.

Poster discussion: CL: Upper and Lower GI 2

PD-0534 Dose-escalation phase III trial of preoperative chemoradiotherapy in rectal cancer. First results F. Lopez Campos 1 , M. Martín Martín 2 , R. Isabel 3 , B. Belinchon 3 , V. Morillo 4 , E. Jorda 5 , P. Peleteiro 6 , F.J. Fuertes 7 , R. Matute 3 , M.D. De las Peñas Cabrera 8 , A. Hervás 9 , V. Duque 2 , A. Caminoa-Lizarralbe 10 , J. Die 11 , J.C. García Pérez 11 , V. Pachón 12 , R. Ferreiro 12 , R. García Latorre 13 , E. Canales 13 , I. Moreno 11 , E. Torabuela 11 , J.D. Pina 11 , P. Abadia 11 , R. Morera 3 , S. Sancho 2 1 Hospital Universitario Ramon y Cajal, Radiation Oncology, Madrid, Spain ; 2 Hospital Universitario Ramón y Cajal, Radiation Oncology, Madrid, Spain ; 3 Hospital Universitario La Paz, Radiation Oncology, Madrid, Spain ; 4 Hospital Provincial de Castellón, Radiation Oncology, Castellón, Spain ; 5 Hospital Clínico Universitario de Valencia, Radiation Oncology, Valencia, Spain ; 6 Hospital Clínico Universitario de Santiago de Compostela, Radiation Oncology, Santiago de Compostela, Spain ; 7 Hospital Universitario de Basurto, Radiation Oncology, Bilbao, Spain ; 8 Hospital Rey Juan Carlos, Radiation Oncology, Móstoles, Spain ; 9 Hospital Universitario Ramón y Cajal, Radiation Oncology, Madrid, Spain ; 10 Hospital Universitario Ramón y Cajal, Anatomical Pathology, Madrid, Spain ; 11 Hospital Universitario Ramón y Cajal, Surgery, Madrid, Spain ; 12 Hospital Universitario Ramón y Cajal, Medical Oncology, Madrid, Spain ; 13 Hospital Universitario Ramón y Cajal, Radiology, Madrid, Spain Purpose or Objective Neoadjuvant chemoradiation followed by surgery is the standard of care for locally advanced rectal cancer (LARC). Dose-response curves suggest that higher doses of radiotherapy improve the complete response rate in LARC. The aim of this study is to evaluate the increase of radiation dose administered in patients diagnosed with