Cancer is a major social problem, and it is the main cause of death between the ages 45-65 years. In the treatment of cancer, radio therapy (RT) plays an essential role. RT with hadrons (protons and light ions), due to their unique physical and radiobiological properties, offers several advantages over photons for specific cancer types. In particular, they penetrate the patient with minimal diffusion, they deposit maximum energy at the end of their range, and they can be shaped as narrow focused and scanned pencil beams of variable penetration depth. Although significant progress has been made in the use of particle beams for cancer treatment, an extensive research and development program is still needed to maximize the healthcare benefits from these therapies. The Optimization of Medical Accelerators (OMA) is the aim of the here-proposed European Training Network, in line with the requirements of the EC’s Medical Exposure Directive. OMA joins universities, research centers and clinical facilities with industry partners to address the challenges in treatment facility design and optimization, numerical simulations for the development of advanced treatment schemes, and in beam imaging and treatment monitoring. The proposed R&D program ranges from life sciences (oncology, cell and micro biology and medical imaging.), physics and accelerator sciences, mathematics and IT, to engineering. It is hence ideally suited for an innovative training of early stage researchers. By closely linking all above research areas, OMA will provide an interdisciplinary education to its Fellows. This will equip them with solid knowledge also in research areas adjacent to their core research field, as well as with business competences and hence give them a perfect basis for a career in research.