The Effects of Radiation Therapy on Bones

Radiation therapy is also called radiotherapy and it uses high-energy X-rays to keep cancer cells from growing. There are a number of different procedures that deliver this radiation to cancer cells. The most common of these is external radiation therapy, in which the X-rays are conducted through radioactive material outside the body and directed through a machine to the cancer site.

Makeup of Bones

• In order to understand the effects of radiation therapy on bones, you must understand the composition of bones. Bones comprise nongrowing, mineral bone and limited regions within which bone growth occurs. The growth region of bones consists of cavities of bone marrow that contain hematopoietic stem cells that form the blood cells. A typical bone contains a shaft of compact bone, or the diaphysis that surrounds a marrow cavity. The shaft end, or epiphysis, is made up of spongy bone covered with a layer of compact bone.

How Radiation Therapy Affects Bones

• The mineral bone is the largest component of the skeleton and not very sensitive to radiation. Even at the levels where environmental and occupational radiation exposure may be considered a risk to other systems of the body, the mineral bone component remains unaffected. The area of the bones that is at high risk from radiation is the active marrow, because this is the area where blood cells are formed. The blood cells during various stages of development are also found in the active marrow, hence this is the area that is at most risk during radiation.

  The other osteogenic, or bone-forming, cells are also at risk because they are not only responsible for the formation of new bone but also for bone resorption. So the nongrowing portions of the bone are resistant to radiation even at high radiation doses. However damage can occur to the cartilage of growing bones, particularly in children's bones or bones that are healing after fractures.

  Because radiation kills osteoblasts, or bone-building cells, women receiving radiation for breast cancer have an increased risk for vertebral fractures and people getting radiation in the abdominal area are at increased risk for hip and pelvic fractures.