Apr. 11, 2005 SCOTTSDALE, Ariz. -- Patients with prostate cancer stand to benefit from new imaging techniques that ultimately allow for concentrated radiation therapy specific to the site of the cancer, part of a promising Mayo Clinic research study.
Administration of this targeted therapy means that healthy surrounding tissue could be spared - a technique called intensity-modulated radiation therapy (IMRT).
The new, cutting edge technique could underscore an evolution in targeting and treatment of prostate cancer, according to lead author of the study, Steven Schild, M.D., radiation oncologist, Mayo Clinic. Dr. Schild and his team of researchers in Arizona presented the study's findings at the recent 90th Scientific Assembly and Annual Meeting of the Radiological Society of North America in Chicago.
Mayo Clinic researchers use new scans, called ProstaScint, fused with CT images of the pelvic region, to target "hot spots" within the prostate. The rationale is to use the CT-derived data to localize the prostate and ProstaScint scan to localize the tumor cells within the prostate to better deliver concentrated radiotherapy to the tumor itself. According to Dr. Schild, as radiation therapy continues to progress, the new imaging techniques, such as ProstaScint and CT images, show promise in the development of more sophisticated pinpointing of prostate tumors.
Dr. Schild and colleagues worked with 43 patients with prostate cancer to administer radiation treatment doses to the entire prostate. A dose of 75.6 Gy over 42 fractions was administered to the entire prostate, using data from the CT images. (A Gy is a "gray," or a measure of the absorbed dose of radiation. One Gy is equivalent to 100 rads, or "radiation absorbed dose.") Strict limits were set for how much radiation could be given to the bladder and rectum in order to minimize side effects of treatment.
Because the ProtaScint scans were able to reveal the tumor location within the prostate gland, the dose of radiotherapy to the cancer could be boosted to 82 Gy - a stronger, more therapeutic dose.
Of the 43 patients, 38 were followed for at least one month after radiotherapy and showed promising results. Only one patient had complications that resulted in urinary frequency at one-hour intervals - a matter that was resolved within one month after completing the therapy. Sixty percent of the participants experienced mild genitourinary toxicity symptoms that could be successfully treated with drugs.
Prostate-specific antigen (PSA) levels (a tumor marker) of the study patients dropped from an average of 6.9 before treatment to 1.9 following therapy. This indicates a favorable initial response to therapy. Because the technology is new, long-term follo-up on patients is still limited. But Mayo Clinic researchers are encouraged by the results using the ProstaScint scans. The ProstaScint scans also appear to improve the accuracy of the staging process for prostate cancer. The integration of newer imaging techniques will be key to improving radiotherapy for many cancers.
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