Abstract Introduction Adjuvant radiation therapy (RT) following primary surgery in women affected by early breast cancer (EBC) plays a central role in reducing local recurrences and overall mortality. The FAST‐FORWARD trial recently demonstrated that 1‐week hypofractionated adjuvant RT is not inferior to the standard schedule in terms of local relapse, cosmetic outcomes and toxicity. The aim of this in silico study was to evaluate the dosimetric aspects of a 1‐week RT course, administered through volumetric modulated arc therapy (VMAT), compared with traditional three‐dimensional conformal radiation therapy (3D‐CRT) with tangential fields. Methods Patients affected by left‐side EBC undergoing adjuvant RT were selected. ESTRO guidelines for the clinical target volume (CTV) delineation and FAST‐FORWARD protocol for CTV to planning target volume (PTV) margin definition were followed. Total prescribed dose was 26 Gy in five fractions. The homogeneity index (HI) and the global conformity index (GCI) were taken into account for planning and dose distribution optimisation purposes. Both 3D‐CRT tangential fields and VMAT plans were generated for each patient. Results The analysis included 21 patients. PTV coverage comparison between 3D‐CRT and VMAT plans showed significant increases for GCI (P