Radiation Therapy: Radiation therapy uses high-energy ionizing radiation to destroy cancer cells and treat or control cancer. Radiation therapy's cancer-causing potential was recognized many years ago. In fact, much of our knowledge about ionizing radiation has come from studying the survivors of the atomic bombs and their radiation in Japan, from workers' occupational exposure to radiation, and from patients treated with radiation therapy for malignant and nonmalignant disease. Despite being relatively rare, the development of a second cancer is more common among those who receive radiation therapy than those who do not.

It's a fine balance. You have to weigh the risk against the medical benefit. If you have a cancer and you're going to be treated with radiation, you should be concerned about the risk of developing a second cancer, but not to the extent that you turn down possible treatment. On the other hand, you should certainly discuss the treatment options fully with your doctor.

Most cases of leukemia related to radiation exposure develop within a few years of exposure, peaking at five to nine years then slowly declining. Most other forms of cancer do not occur until ten years after radiation exposure, and some cancers are diagnosed even fifteen or more years later. Radiation-related leukemia risk depends on a number of factors, such as the amount of radiation received, the percentage of bone marrow exposed to radiation, and whether the patient was also treated with chemotherapy.

Studies of radiation-related breast cancer have found the greatest risk in women who were irradiated as children and adolescents for other conditions. (The most common reason for adolescents to have chest radiation is Hodgkin's disease, a type of lymphoma.) Oncologists (doctors specializing in cancer treatment) know about the increased risk of breast cancer in these women and generally recommend that they have vigilant lifetime screening for breast cancer. However, most studies of individuals with Hodgkin's disease have found no increased breast cancer risk among women who receive radiation at 30 years and older.

X-rays and Mammography: Many people are concerned about their exposure to x-rays. X-rays (including mammograms, x-rays of the breast) use doses of radiation that are many times lower than those used in radiation therapy. As with radiation therapy, studies in the past have shown that there appears to be some risk in receiving many x-ray examinations, particularly for children who have multiple x-rays. The level of radiation in modern x-rays is much lower than that used even 25 years ago and poses much less of a risk. While it's a good idea to minimize repeat exposures whenever possible, especially in children, it's important not to avoid necessary x-rays.

CT Scans: Computed tomography (CT) scans use larger doses of radiation than those found in conventional x-rays. Again, concern has been raised over the possibility of an increased cancer risk in children who receive multiple CT scans. Ways to lower radiation doses without compromising medical value are encouraged.

Another potential source of exposure to radiation are whole-body CT scans, which some people are now requesting as part of a regular health checkup as a way to screen for cancer and other diseases. Many groups, including the PDA, have expressed concern over this practice because there is little evidence of its usefulness, and it exposes people to unnecessary radiation. Sometimes CT scans are available in shopping malls. They are advertising for healthy people to come in and get whole-body scans. This is unnecessary and inappropriate.

However, whole-body CT scans do have their place. They can save the lives of accident victims who need quick evaluation to determine if they have a ruptured spleen or punctured lung. They are also effective in diagnosing some chronic conditions.