Predictors of radiation sensitivity and resistance

Local control of tumor is a very important predictor of outcome in all cancer patients, including quality of life and survival. Local tumor failure is the cause of 40-60% of cancer deaths, and may occur in 60-80% of cancer patients at the time of death. Any process that enhances tumor cell kill for a given radiation dose (sensitization) is important, and investigators have focused on three tumor parameters that are likely to influence local tumor control after radiotherapy: intrinsic radiosensitivity, the degree of tumor hypoxia, and the rate of repopulation of tumor cells. In this chapter, we will discuss these three parameters as well as modifiers of radiation effects. Any factor that decreases the relative amount of normal tissue injury is also important and can affect the therapeutic benefit of treatment. We will discuss these factors as well (Figure 17.1).