Although three-dimensional conformal radiotherapy (3D-CRT) remains the gold standard as a curative treatment for NSCLC when surgery is not possible, intensity modulated radiotherapy (IMRT) is increasingly used routinely. The purpose of this study was to assess the clinical (immediate toxicities) and dosimetric impact of IMRT compared to 3D-CRT in the treatment of locally advanced (stages IIIA to IIIC) non-small cell lung cancer (NSCLC) treated with concomitant radiochemotherapy, while IMRT in lung cancer was implemented in the radiotherapy department of the Jean-Perrin Center. Between March 2015 and October 2019, 64 patients treated with concomitant radiochemotherapy were retrospectively included. Thirty-two received 3D-CRT and 32 IMRT. The radiotherapy prescription was 66Gy in 33 fractions of 2Gy. IMRT has improved coverage of target volumes (V95 increased by 14.81% in IMRT; P<0.001) without increasing doses to OARs and reducing dysphagia (RR=0.67; P=0.027). Low doses to the lung were not significantly increased in IMRT (pulmonary V5 increased by 7.46% in IMRT). Intensity modulated radiotherapy, compared with the standard RC3D technique, improve the coverage of target volumes without increasing the dose to the OARs. It also improves the immediate tolerance of the treatment by reducing the number of dysphagia. Copyright © 2021. Published by Elsevier Masson SAS.