Alternatively, with adjustment of radiation dose, if necessary an improved therapeutic index requires that there be increased anti-tumor effects for equivalent toxic side effects. Some drugs used to enhance radiation effects are called radiation sensitizers. These sensitizers mimic what oxygen does in the tumor cells, to increase the radiation damage and therefore improve outcome. Drugs like Mitomycin are toxic to cells in low oxygen conditions - an interesting possibility to help eradicate tumors often present at less than optimal oxygen concentrations. Most oncologists believe that oxygen must be within a tumor for radiation to effectively kill cancers.
Radiation is given in fractions or intervals.
Cells that survive these intervals and repopulate are called repopulated cells. Normal cells repair damage caused by radiation while repopulation of cancer cells is often manifested as resistance to treatment. Exactly how drugs and radiation are given together is a subject of much study. Its goal is to diminish the scope of surgery or radiation necessary. Sites where combined modality therapy are commonly administered have been outlined.