February 7, 2007. — More than ninety percent of men who receive appropriate radiation dose levels with permanent radiation seed implants to treat their early-stage prostate cancer remain recurrence-free eight years after diagnosis, according to a study released in the February 1 issue of the International Journal for Radiation Oncology*Biology*Physics, the official journal of ASTRO.
"The only controllable factor to impact on long-term outcome," the study states, "was the D90 which is a reflection of implant quality." Whether the isotope used to achieve adequate dose was iodine 125 (I-125) or palladium 103 (P-103) "was not significant," the study authors found.
Other, non-controllable factors that influenced treatment outcome after permanent brachytherapy for prostate cancer, the authors report, are tumor stage, Gleason score, pretreatment PSA, treatment year, and post-brachytherapy "dosimetric quality." PSA nadir below or equal to 0.5 ng/mL "was particularly associated with durable long-term PSA disease-free survival."
The importance of dose
D90 is the dose of radiation delivered to 90% of the prostate, measured in grays. The gray (Gy) is a unit used to measure a quantity called absorbed dose. Absorbed dose is the amount of energy actually taken in by tissue exposed to the radioactive energy put out, in the case of brachytherapy, by the seed implants.
"Among patients where the I-125 dose to 90% of the prostate (D90) was at or higher than 130 Gy," the study authors state, "the 8-year PSA relapse-free survival (PRFS) was 93% compared with 76% for those with lower D90 dose levels." Some radiation oncologists are equipped, trained, experienced and competent so as to make sure their patients' prostates are likely to receive the adequate, higher dose. Others are less so.
Results for the entire group of men treated in these eleven leading centers show a more shaded picture. Taking 8 year PSA relapse- free survival as the goal, and ranking the prostate cancer risk before treatment: :
- low risk prostate cancer, goal reached by 82%
- intermediate risk, by 70%
- high-risk prostate cancer, by 48%
Seed implants are now a widely-accepted treatment option for early stage prostate cancer. The method is less invasive than surgery and quicker than external beam radiation. The seeds, similar in size to a grain of rice, if properly implanted deliver concentrated radiation to the prostate while sparing surrounding organs and tissue.
Patients treated with seed implants may avoid immediate side effects common after surgical treatment. Urinary bother may occur and persist but risk of incontinence is lessened and impotence, if it occurs, may be delayed by years.
Doctors in this study evaluated the long-term results of permanent seed implants in men with early-stage, T1-T2 prostate cancer. Nearly 2,700 men were studied at 11 institutions in the United States over eight years. About two thirds of the men (68%) were treated with I-25 seeds ( median dose, 144 Gy) and the rest with Pd-103 seeds (median dose, 130 Gy) . The radioactive seeds were administered with the aid of ultrasound-guided techniques to accurately place the seeds in the prostate gland. The implant method applied is known as intraoperative real-time conformal planning technique with inverse planning optimization . All patients received the seed implants as the sole treatment for prostate cancer with no additional chemotherapy or radiation therapy.
"This study is exciting because it shows that brachytherapy alone without additional surgery, radiation or drugs can be effective at curing early-stage prostate cancer," said Michael J. Zelefsky, M.D., lead author of the study and Chief of Brachytherapy Services at Memorial Sloan-Kettering Cancer Center in New York. "These results also confirm other findings that the quality of the seed implant is a critical ingredient for achieving a better outcome."
Medical centers participating in the study were Memorial Sloan-Kettering Cancer in New York, M.D. Anderson Cancer Center in Houston, New York Prostate Institute in Oceanside, N.Y., Arizona Oncology Services in Scottsdale, Ariz., Seattle Prostate Institute in Seattle, Chicago Prostate Institute in Chicago, Cleveland Clinic Foundation in Cleveland, Massachusetts General Hospital in Boston, Mayo Clinic in Rochester, Minn., University of Michigan Medical School in Ann Arbor, Mich., and Fox Chase Cancer Center in Philadelphia.
Sources & Links
Multi-institutional analysis of long-term outcome for stages T1-T2 prostate cancer treated with permanent seed implantation.
Zelefsky MJ, Kuban DA, Levy LB, Potters L, Beyer DC, Blasko JC, Moran BJ, Ciezki JP, Zietman AL, Pisansky TM, Elshaikh M, Horwitz EM. Int J Radiat Oncol Biol Phys. 2007 Feb 1;67(2):327-33.
Radiation Related Terms Radiation Information Network, Idaho State University
For more information about prostate cancer treatment options, please visit http://www.rtanswers.org.
Pomegranate Juice Slows PSA Rise in men With Recurrent Prostate Cancer After Surgery, Radiation
