Higher Radiation Doses Cure More Patients with Prostate Cancer
Cancer of the prostate, a male sex gland located near the bladder and rectum, is a type of cancer that occurs commonly in older men. Treatment for prostate cancer depends on the stage of disease (extent of disease at the time of diagnosis), and may include surgery, radiation therapy, hormone therapy, chemotherapy, and/or biologic therapy to help the immune system fight the cancer.
Two of the most common treatments for localized prostate cancer are radiation therapy and a surgical procedure, called a radical prostatectomy. Radiation therapy and radical prostatectomy are equally effective treatments against localized prostate cancer and the choice of treatment often depends on the personal preferences of the patient and his physician.
Radiation therapy involves the directing of high-energy X-rays to the affected area of the body, to kill cancer cells. If radiation is selected as the form of treatment for prostate cancer it is important to know that there are variations in the manner in which radiation is delivered which can affect outcomes of treatment.
Doctors at the Cleveland Clinic Foundation evaluated 1041 consecutive patients with localized prostate cancer who were treated with external beam radiation therapy. They divided up the patients into those who received a below average or above average radiation dose of 72Gy. Patients receiving radiation doses above the average had a five year survival of 87% compared to 55% for patients receiving below average radiation doses. Clinical relapses occurred in 5% of patients receiving higher than average radiation doses compared to 12% of patients receiving lower than average radiation doses.
Based on these results these doctors were able to recommend radiation doses based on risk of relapse for 6 subgroups of patients with the lowest risk patients receiving 70-73 Gy and the highest risk groups receiving 80-90 Gy with an intermediate risk group receiving 75-85 Gy. These risk groups are determined by the level of PSA and the Gleason score obtained by looking at the cancer under the microscope.
In order to deliver high doses of radiation therapy without excessive toxicities a technique called three-dimensional conformal radiation therapy is used. This allows radiation to be delivered more accurately to the cancer while sparing normal tissue. It is estimated that less than half the patients receiving radiation therapy for prostate cancer are treated with three-dimensional conformal radiation therapy. (International Journal of Raniation Oncology Biology and Physics, vol 46, Issue No 3 pages 567-574, 2000)
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