RADIATION THERAPY FOR PROSTATE CANCER: EXTERNAL-BEAM THERAPY
How does an X-ray machine work? The simplest way to think of it is to imagine yourself getting a suntan. The difference here is that you can’t feel or see the X-ray energy hitting your body, and the “tan” occurs internally. (What happens is that the radiation particles destroy DNA, causing targeted cells to die.) The best way to get a good, even tan is in increments, not all at once. Similarly, the most effective radiation doses are spread out over several weeks, with each treatment lasting only a few minutes at a time. (The goal here, besides killing the prostate cancer, is to do as little harm as possible to the surrounding tissue—the rectum, bowel, bladder, bone, and skin.)
To help your radiation oncologists get a good picture of the terrain of the targeted area—the prostate and surrounding organs—you will probably be given a “treatment-planning” CT scan. Some doctors also use computer simulators to fine-tune the dose of radiation and fields of treatment for you—these can vary, depending on factors such as the stage and grade of your tumor, the contour of your pelvis, and your size (for some large or heavyset men, a different degree of energy works better).
For high-grade tumors (Gleason score 7 or higher) or malignancies greater than clinical stage T2b (B1), doctors make sure the field of treatment covers the prostate, seminal vesicles and surrounding tissue, including nearby lymph nodes, where the cancer may have spread after penetrating the prostate wall. Radiation is delivered to the front, back and each side of the patient. (The specific map of treatment can vary from man to man.) A major goal here is to safeguard as much of the surrounding territory—the cancer-free organs and tissue—as possible. Doctors particularly want to shield bone from radiation, to avoid harming key blood-forming cells that reside in the bone marrow. One way to protect cancer-free areas is to shield them with blocks of lead, which the radiation can’t penetrate. Other steps can also be taken—one way to protect the bowel, for instance, is for the patient to have a full bladder during treatment; this pushes the bowel away from the pelvis. Another technique is to have the patient lie on a hard pillow that pushes the bowel out of the way, into the upper abdomen.
To make treatment easier to tolerate (and thus minimize side effects), a “sandwich” approach—in which the radiation dose is split in two, with a break in between—may become more common. The purpose of this technique is to give the bowel and part of the bladder a “breather,” a window of opportunity to recover from the shock of the treatment. In men who have small (stage T1 or T2, or A and B), low-grade tumors—where the risk of cancer having spread beyond the prostate is minuscule—radiation is limited to the prostate alone.
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