The discovery of X-rays in 1895 by Wilhelm Conrad Röntgen paved the way to a new scientific epoch in the management of cancer. Today, with the XXI century in sight, radiotherapy has matured and has become one of the mainstays in the management of cancer. Although long-term success with the use of ionizing radiation in cancer treatment can be achieved in about half of our patients, significant improvements in tumor control rates and/or reduction in side effects (i.e. quality of life) are needed. As a future perspective, the authors highlight the gains that can be anticipated from research in the field of 3-D conformal radiotherapy, in particular with regard to sparing critical structures (e.g. parotid glands) in cancers of the head & neck.