Tissue response models

The risk of radiation effects to normal tissues is an important factor, both in the process of considering radiotherapy and in the optimization of personalized radiotherapy for individual patients. Severe toxicity may cause a lifelong reduction in quality of life and sometimes the risk of morbidity even limits dose and efficacy of the treatment. Developments in treatment technology have increased the possibilities to reduce dose to normal tissues. Moreover, the same developments have also increased the number of ways to influence numerous characteristics of the three-dimensional dose distribution. For example, multi-leaf collimators offer increased control of beam shapes. Increasing computation power improves the ability of treatment planning systems to handle an increasing number of beams, or even rotational techniques. Finally the availability of particle therapy offers beams with entirely new dose-depth curves and for heavier ions even variations in the biological effects of dose