Brachytherapy delivers radiation internally by implanting radioactive "seeds" about the size of a small grain of rice. The radiation damages the cell's DNA, triggering cell death. According to the American Cancer Society, there are two types of prostate brachytherapy: Low-dose rate brachytherapy permanently implants the radioactive seeds into the prostate. High-dose rate brachytherapy places tiny catheters into the prostate surrounding the tumor. High-intensity radiation seeds are inserted into the catheters for a few minutes and then removed. The procedure is repeated over a few days to deliver a much higher overall dose than the low-dose method.
Low-Dose Rate Brachytherapy
According to the Seattle Prostate Treatment Center, where prostate brachytherapy was pioneered in the United States, in the low-dose rate brachytherapy method, the doctor inserts a needle through the perineum into the prostate. The perineum is the area between the scrotum and anus. Using imaging guidance, the doctor deposits a string of radioactive seeds in precise rows according to the map developed during a previous imaging study of the tumor. The doctor repeats this procedure several times until 40 to 100 seeds are placed in a grid pattern surrounding the tumor to ensure the optimum radiation dose. The seeds remain permanently in place, slowly irradiating the tumor over several weeks or months until the radiation is used up.
High-Dose Rate Brachytherapy
According to the Prostate Cancer Research Institute, the high-dose procedure involves the insertion of tiny hollow tubes, or catheters, into the prostate in a grid pattern surrounding the tumor. Once in place, a single high-intensity radiation seed is inserted into each catheter for a predetermined amount of time and then removed. The catheters remain in place over the course of treatment, which usually takes a couple of days. Once complete, the catheters are removed.
Imaging and Mapping
Before either type of brachytherapy procedure, the American Cancer Society states that the doctor performs an image study using one or a combination of imaging methods including ultra sound, computed tomography, or CT scan, and magnetic resonance imaging, or MRI. The images show the exact location of the tumor or tumors within the prostate. They also allow the doctor to measure the volume of the prostate and tumors. The doctor enters this data into treatment planning software to develop a precise map for placing the radiation seeds, and calculates the precise dose needed for the size of the tumor or tumors. This ensures delivery of the optimal radiation dose to eradicate the tumor while minimizing the damage to normal tissues.
