Therapeutic radiation physics primer.

Radiation biology is the discipline of radiation oncology that studies the effects of radiation on cells, tissues, and organisms. Over the past decades, insights into radiobiologic mechanisms have provided rational bases for the use of increased radiation doses and fractionated treatment regimens to maximize the effect on cancers while limiting radiation injury to the surrounding normal tissues. In this article, the authors discuss the terminology of radiosensitivity and some of the factors that determine the radiation response of malignant tumors and normal tissues. Although the field of radiation biology is rapidly evolving, a thorough understanding of the established factors that determine radiation responses will remain an important prerequisite for the successful application of multimodality cancer therapies and molecularly targeted approaches.