How is radiation therapy used in prostate cancer
treatment?
Radiation therapy is widely used in definitive (curative), adjuvant, and
palliative treatment of prostate cancer. In radiation therapy (also called
radiotherapy), high-energy X-rays are used to damage cancer cells and stop them
from growing and dividing. Like surgery, radiation therapy is local therapy; it
can affect cancer cells only in the treated area. In early stage prostate
cancer, radiation can be used instead of surgery, or it may be used after
surgery to destroy any cancer cells that may remain in the area. In metastatic
diseases, it may be given to relieve pain or other problems.
Radiation may be directed at the body by a machine (external beam irradiation),
or it may come from a small container of radioactive material placed directly
into or near the tumor (radioactive seed implant, or brachytherapy). Some
patients receive both kinds of radiation therapy.
For external radiation therapy for prostate cancer, the patient is treated in an
outpatient department of a hospital or clinic. Treatment generally is given 5
days a week for about 6 weeks. This schedule helps protect healthy tissues by
spreading out the total dose of radiation. The rays are aimed at the pelvis. At
the end of treatment, an extra "boost" of radiation is often directed
at a smaller area, where the tumor developed.
Studies have shown that prophylactic irradiation of clinically or pathologically
uninvolved pelvic lymph nodes does not appear to improve overall survival or
prostate cancer-specific survival. However, pelvic irradiation may significantly
decrease the local recurrence in the pelvis in some patients.
Long-term results with radiation therapy are dependent on stage. A review of 999
patients treated with irradiation showed cause-specific survival rates to be
significantly different at 10 years by T-stage: T1 (80%), T2 (65%), T3 (55%),
and T4 (20%). An initial serum prostate-specific antigen (PSA) level of greater
than 15 ng/mL is a predictor of probable failure with conventional radiation
therapy.
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