1. What is the extent of the dosimetric benefit of DIBH compared to free-breathing radiotherapy? For adult patients with breast cancer, malignant lymphoma, and lung cancer, radiotherapy delivered in DIBH compared to free-breathing significantly lowers the dose to the heart, lungs, and stomach. However, for very young patients the anatomical changes (i.e. inflation of the lungs, increased separation of the heart and the tumor) might be less pronounced than for adults hampering the dosimetric advantage of DIBH.