Radiation Oncology in Florida

Three-Dimensional Conformal Radiation Therapy (3-D CRT) at Mayo Clinic Jacksonville

Three-dimensional conformal radiation therapy is particularly useful in treating prostate cancer.

Enlarge

Cancer cells grow and divide more rapidly than the normal cells around them. In radiation therapy, high-energy X-rays are directed at a tumor to kill or damage cancer cells so they cannot grow or spread. Unlike chemotherapy, which exposes the entire body to cancer-fighting chemicals, radiation therapy affects only the tumor and surrounding area. The challenge is to deliver the radiation so it effectively targets the tumor without damaging normal tissue.

Three-dimensional conformal radiation therapy (3-D CRT) combines digital diagnostic imaging, powerful computers and specialized software to conform the radiation beam to the shape of the tumor. This technique is commonly used to treat cancers in most parts of the body but is particularly useful in treating prostate cancer, lung cancer and certain brain tumors.

Treatment planning begins with CT or MR images that show the anatomy of the tumor and surrounding normal structures. These images are put into a special treatment planning computer that produces an accurate three dimensional image of the tumor and surrounding organs so that multiple radiation beams can be aimed at the tumor from different directions, matching the contour of the treatment area. This delivers a prescribed dose across all three dimensions (height, width and depth) of the tumor and allows the dose to be spread around the surrounding normal tissue, minimizing the dose to any one area and sparing nearby healthy tissue.

Dosimetrists use the computer to model the effect of a predetermined treatment on a patient. They select beam angles and intensity, put them into the computer and observe the virtual outcome. By trying different combinations on the computer, the best dose distribution is determined.

Further advancements of 3-D therapy have led to the development of intensity modulated radiation therapy (IMRT), also available at Mayo Clinic. With IMRT, not only are beams aimed from several directions, the intensity or strength of the beams can be adjusted to minimize the dose reaching healthy tissue.

For most types of cancer, radiation therapy usually is given five days a week for six or seven weeks. (When radiation is used for palliative care, not for cure, the course of treatment is shorter, usually two to three weeks.) The total radiation dose and number of treatments varies with each patient and depends on the size, location and type of tumor, as well as the patient's general health and other medical treatments he or she is receiving.