Cancer cells reproduce faster than normal cells in the body. Radiation therapy targets these rapidly dividing cells. The radiation reacts with water in the cells and this reaction damages the DNA or genetic material in the cell that controls cell growth.
Normally, cells can repair themselves and continue growing. But since cancer cells can't repair themselves as easily, they die. Although normal cells are also affected, they repair themselves more effectively.
Radiation therapy has undergone major advances in recent years. The use of computers, highly sophisticated equipment and new understandings of how cancer cells work have made radiation safer than ever.
Doctors are extremely careful to limit damage to healthy tissue by:
Precisely targeting radiation beams directly at the cancerous area
Dividing treatments into several small sessions, called fractions
Making sure equipment is in top working order
Using the minimal effective dose
Patients usually receive external beam therapy for five days in a row, with a rest over the weekend. Receiving small frequent doses with brief rests limits damage to healthy cells, while effectively destroying cancer cells.