Normal tissue tolerance

Normal tissue radiation tolerance refers to the response of previously unirradiated tissues to a variety of very different exposure scenarios: total or large partial body exposure with ‘high’ doses in an ‘acute’ manner, e.g., in radiation accidents, or in a more ‘chronic’ way, e.g., through close and permanent contact with radioactive sources. A more localized ‘high’ dose, conformed to specific target structures, is achieved with modern radiotherapy techniques. In contrast, concentration of ‘low’ radiation doses is usually induced with most diagnostic procedures that involve ionizing radiation; however, the latter is also imminent in radiotherapy outside the high-dose structures. The present overview will not include the response of highly sensitive tissues (e.g., the eye lens, gonads, embryo/fetus). Also, the tolerance of normal tissues to radiation induction or promotion of tumours will not be covered. This present review rather focuses on the standard OAR in radiotherapy