NIST Improves Accuracy of Radioactive Seeds Used to Treat Prostate Cancer

Men who opt to treat their prostate cancer with implanted radioactive seeds rather than surgery or external beam radiation now can be assured that their radiation dose is traceable to a new and improved standard at the National Institute of Standards and Technology.

Radioactive prostate seeds minimize the risk of incontinence and impotence, and, as recent hospital studies have shown, may be as effective as surgery or external beam radiation for men with localized prostate cancer. Aside from skin cancer, prostate cancer is the most common cancer in men. The American Cancer Society estimates more than 184,000 new cases are diagnosed yearly in the United States.

Beginning this month, NIST is offering a new calibration service to the manufacturers of radioactive seeds for prostate cancer. At this time, NIST is the only laboratory in the world that offers this service. The American Association of Physicists in Medicine, the Food and Drug Administration and the Nuclear Regulatory Commission require that manufacturers trace the accuracy of their prostate seeds to radiation standards at NIST.

The new and improved NIST standard is a radiation detector that is 100 times more sensitive than the previous detector. The previous standard was applicable only to radioactive seeds containing iodine-125 and of the designs available in 1984. The new detector can determine the radiation exposure from seeds of arbitrary design for either radioactive iodine-125 or palladium-103, both low-energy X-ray emitters.

To determine the exposure from a seed, NIST physicists place the seed right next to the opening of the detector. Radiation from the seed then knocks electrons out of atoms in the air inside the detector. This ionization creates an electrical current that is measured by the detector and then converted to air-kerma strength, a quantity related to X-ray exposure. The corresponding dose to tissue then will be proportional to this calibrated air-kerma strength.

Prostate seeds are about the size of a grain of rice and work by delivering radiation directly to a tumor. A doctor, guided by ultrasound imaging and taking into account the strength of the seeds, inserts the seeds into the tumor in a pattern designed to kill the cancer cells. Significant dose from the seeds extends only a short distance, so the implant pattern can be designed in a way that doesn’t affect tissue much beyond the tumor.

Recent clinical studies suggest that radiation from tiny seeds inserted directly into the prostate may equal the effectiveness of surgery or radiation from an external beam. Such studies have increased dramatically the demand for the radioactive seeds used in the treatment and for accurate dose calibrations of the seeds.

NIST’s new calibration service will help the growing number of prostate seed manufacturers in designing new seeds, meet the growing demand for seeds and give patients confidence in knowing that their radiation dose is accurate.

For more information on the new prostate seed calibration service, contact Paul Lamperti at (301) 975-5591 or paul.lamperti [at] nist.gov (paul[dot]lamperti[at]nist[dot]gov).

As a non-regulatory agency of the U.S. Department of Commerce's Technology Administration, NIST promotes economic growth by working with industry to develop and apply technology, measurements and standards through four partnerships: the Measurement and Standards Laboratories, the Advanced Technology Program, the Manufacturing Extension Partnership and the Baldrige National Quality Program.