Medical imaging progressed to a standard undreamt of not very many years ago. The advances are due to continuous development of radiological techniques and the introduction of magnetic resonance imaging. With the improved and new methods three-dimensional target volumes for radiation therapy can be defined with hitherto unknown precision. This leads to an improvement in irradiation techniques and, as a consequence, to a higher likelihood of tumor control and a lower risk of normal tissue complications. Besides the improvement in irradiation techniques the new imaging methods may enable great strides in tumor response monitoring, not only in the detection of morphological alterations but also by showing physiological changes in the tumor during and after treatment by means of MRI and PET. This not only leads to better prognostic information but may also allow early evaluation of the response to treatment. It may then be possible to individualize the radiation dose but also the alternative-treatment for non-responders. This is certainly a future direction for radiation oncology.