The recent EORTC 10981-22023 AMAROS trial showed that axillary radiotherapy and axillary lymph node dissection provide comparable local control and reduced lymphoedema in the irradiated group. However, no significant differences between the two groups in range of motion and quality of life were reported. It has been acknowledged that axillary irradiation could have induced some toxicity, particularly shoulder function impairment. In fact, conventional breast irradiation by tangential beams has to be modified to achieve full-dose coverage of the axillary nodes, including in the treatment field a larger portion of the shoulder structures. In this scenario, alternative irradiation techniques were discussed. Compared with modern photon techniques, axillary irradiation by proton therapy has the potential for sparing the shoulder without detrimental increase of the medium-to-low doses to the other normal tissues.