Treatment planning begins with a series of CT images that give enough cross-section views of the prostate, seminal vesicles, and surrounding terrain (including the bladder wall, rectal wall, small bowel, bony structures and skin) to create a three-dimensional reconstruction. Dosage, and the area over which it will be distributed, can be calculated plane by plane, millimeter by millimeter. Each radiation beam—the 3-D approach allows more segments of treatment than traditional therapy—is automatically shaped by the computer so the energy focuses on the tumor alone (in the prostate as well as in tissue outside the gland where cancer has spread), rather than its entire neighborhood. A special body cast is custom-built for each patient to minimize movement during a treatment session, and also to make sure that a man’s exact position can be reproduced every time. Several quality-control mechanisms are built into this approach; after-the-fact or instantaneous means of verifying that the radiation went to the right spot for the right length of time help guarantee the most successful treatment possible.
Right now, it’s impossible to predict how well these techniques will work. There’s just not enough information yet to give meaningful results on PSA levels after treatment or to predict long-term survival rates; however, this information should be available within a few years. At eighteen months after treatment in one study, only 3 percent of the men had a local recurrence of cancer (two of these were men with stage T2C, or B2, cancer; and five had stage T3 or T4, or C, disease. The best we can say right now is that early results suggest an excellent potential for 3-D conformal therapy.
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