Radiation therapy is used for treating cancer for the same basic reason as chemotherapy: the possibility (or probability ) that surgery has not been able to remove every last cancer cell. Unlike chemotherapy which travels through the body in the blood stream and supposedly gets to all cancer cells, radiation therapy must be aimed at likely sites of remaining disease. (It would be too toxic for radiation to be aimed at the whole body.) Radiation therapy for cancer is based on the principle that x-ray energy can damage cancer cells, which then die.
As with chemotherapy, normal cells are “innocent bystanders” when radiation is used because it is impossible to aim the radiation at only the cancer cells. It is believed that normal cells recover from radiation better than cancer cells, allowing normal cells to survive as nearby cancer cells die. Nevertheless, there are toxicities to radiation therapy which ultimately limit the dose which can be given. Just as with chemotherapy, there are years of experience treating childhood cancers with radiation, and this guides its use for PPB. Not every child with PPB will or should receive radiation therapy. Generally speaking, the older the child and the greater the amount of tumor cells left after surgery, the more likely will radiation be a part of the overall treatment recommendation.