Radiation treatment more than once?

(CNN) - Asked by Charlotte, Southport, Connecticut:

Is it possible -- in some cases -- to get a second round of radiation? When I had it 25 years ago I was told that this is once-in-a-lifetime treatment, yet a friend of mine is scheduled for a second round.

Expert answer:

Dear Charlotte:  X-ray radiation like that used to take a chest X-ray is used in very high doses by a radiation oncologist to treat cancer. What's important is how it is aimed from the radiation therapy machine and what dose of radiation is given. The dose of absorbed radiation is calculated in units called centigray.

Radiation therapy is a wonderful tool used to treat and often cure many cancers when the cancer is localized to one place in the body. In select cases, radiation therapy can be used a second time in the same patient. If cancer is being treated in a different area of the body, this is an easy question. Each organ can receive a limited amount of radiation before it is permanently damaged by radiation, and each type of cancer needs a certain amount of radiation for cure.

Questions that must be asked by the radiation oncologist planning the therapy include: "Is the same area of the body being irradiated as was irradiated before?" "How much radiation was given to that site before and how much radiation is needed to kill this second particular cancer?" The physician will want to get records of the previous radiation, and the decision to radiate a second time frequently requires computer simulation (radiation planning).

Dr. Otis Brawley
Chief Medical Officer,
American Cancer Society