Radiosensitivity defines the sensitivity level of each patient to the radiation used in radiation therapy.

More precisely, radiosensitivity defines the sensitivity level of a cell, organ, tissue, or tumor to irradiation: the part of cells, tissue or tumor that will die in response to irradiation. 

Each patient and each tumor will react differently to the same dose of radiotherapy. This individual sensitivity is related to genetic variations among individuals and among tumors. 


Some environmental factors also can influence the radiosensitivity of tissues. For example, smoking increases the sensitivity of healthy tissues to radiation, and consequently also the risk of toxicity.