Prostate Cancer Treatment Comparison: Seed Implantation Shows More Side Effects than External Radiation
Nov. 6, 2001 – Treating prostate cancer with implanted radioactive "seeds" may yield more side effects than previously thought. Researchers at Washington University School of Medicine in St. Louis found that patients treated with seed implants report more disruptions in their quality of life for the first year following treatment than those treated with modern external beam radiation therapy.
Jeff M. Michalski, M.D., assistant professor of radiation oncology, presented the findings today at the 43rd annual meeting of the American Society for Therapeutic Radiology and Oncology in San Francisco.
According to Michalski, most physicians believe seed implantation, known as brachytherapy, is a better treatment option than high quality conformal external-beam radiation therapy.
"Without question, brachytherapy is an effective treatment for eradicating cancer, and I think the long-term complication rate is acceptable," he says. "But brachytherapy doesn't appear to be the definitive, better treatment of the two. Physicians should caution their patients that it may cause more side effects than modern external-beam radiation therapy."
Three-dimensional conformal radiation therapy, an advanced form of external-beam radiation therapy, delivers a beam of radiation to a tumor while preserving as much healthy tissue as possible. It is a daily 20-minute outpatient procedure that requires treatment five days a week for seven and a half weeks followed by routine quarterly check-ups.
Prostate brachytherapy is an invasive outpatient procedure that requires either general or spinal anesthesia. Physicians permanently implant 75 to 125 tiny radioactive pellets, or seeds, into the prostate gland, depending on the gland's size and shape. Patients return for a follow-up exam three weeks after implantation, and then quarterly check-ups. Seeds made of palladium remain radioactive for six to nine weeks; iodine seeds remain radioactive for six to nine months.
Michalski and his colleagues administered brachytherapy to 182 men and three-dimensional conformal radiation therapy to 87 men. Each participant chose his own type of therapy. Participants' average age was 70.
During follow-up visits over slightly more than 2 years, patients were asked to fill out several standard questionnaires including: the International Prostate Symptom Score, a measure of difficulty emptying the bladder; the FACT-P, a measure of a patient's sense of well-being following cancer therapy; and the Sexual Adjustment Questionnaire.
Patients who underwent brachytherapy reported significantly more urinary, sexual and bowel problems than men treated with external-beam radiation. For example, the mean cumulative International Prostate Symptom Score for brachytherapy patients was 12.5 compared to 8.3 for men who received external-beam radiation.
Differences between the two groups were most dramatic in the first six to nine months following treatment, with some differences persisting for a year or more. Men who received brachytherapy had greater urinary complications. They also were less likely to resume sexual activity within six months of treatment and engaged in sexual activity less often than participants who received external-beam radiation therapy.
Michalski suggests two reasons why brachytherapy may lower quality of life more than conformal-beam radiation therapy. Because the procedure is invasive it causes the gland to swell. Swollen glands can cause discomfort and may take several months to recover.
Second, the urethra, the tube that channels urine and semen outside the body, passes through the prostate gland and may therefore get a higher dose of radiation from brachytherapy than from external-beam radiation therapy. Higher levels of radiation to the urethra may be responsible for the subsequent urinary problems.
But according to Michalski, "most patients choose brachytherapy because it is a one-day treatment while external-beam therapy requires seven and a half weeks of daily treatments." Many also prefer brachytherapy based on what they hear from friends or relatives and learn from the Internet, he says.
"When patients are convinced they want brachytherapy, I don't try to talk them out it," says Michalski. "But I do explain that they might experience some acute, short-term side effects with brachytherapy that may affect their sense of well-being. I also tell them that those side effects may disappear within a year."
Michalski's team next plans to examine whether differences in factors such as radiation dose distribution, type of isotope and strength of isotope might influence the occurrence of side effects.
Washington University School of Medicine, Office of Medical Public Affairs,
Washington University School of Medicine at Washington University Medical
Center, Campus Box 8508, 4444 Forest Park Ave., St. Louis MO 63108-2259,
(314) 286-0100 FAX: (314) 286-0199
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