Real-Time Dosimetry

Physicians at Virginia Mason use an advanced technique known as real-time dosimetry prostate seed brachytherapy implant. This technique allows the most precise placement of radioactive seeds into the prostate with millimeter accuracy. The traditional pre-plan method requires a preoperative ultrasound study in which the patient's position must be matched exactly at the time of the implant. Matching this position in the operating room is often difficult and can result in inaccurate placement of seeds. The real-time technique avoids this problem by using a computer system in the operating room to map the prostate gland. In addition, it also gives the physician the ability to precisely track the position of each seed as it is placed, ensuring proper radiation dose within the prostate. Equally important, this technique helps physicians avoid the placement of seeds near normal tissues such as the bladder, urethra, and rectum, thus minimizing toxicity.

Patients undergo either general or spinal anesthesia. Needles are placed through the skin of the perineum (the space between the anus and scrotum) and into the prostate. An ultrasound probe in the rectum helps guide the needles into their proper position. The seeds are then placed into the prostate through each needle. As each needle is withdrawn, it leaves behind a row of seeds.

The radioactive isotopes used include iodine-125 and palladium-103, which have a half-life of 60 and 17 days, respectively. The newest isotope, called cesium-131, is also available at Virginia Mason, and has a half-life of 9 days. The amount of radioactivity that escapes the body is exceedingly small. As a safety precaution, however, we recommend that small children and pregnant women do not sit on or next to the patient for 1-2 months.