Brachytherapy treats prostate cancer interstitially by delivering concentrated doses of radiation within the tissue. There are two types of brachytherapy: low dose radiation (LDR) which is permanent and high dose radiation (HDR) which is temporary. There are currently no studies that can conclude that one type of brachytherapy is more effective than the other, nor are the side effects of either treatment radically different. The tools for temporary brachytherapy require that the prostate cancer patient stay over night in the hospital. Permanent brachytherapy requires an overnight stay only if the stay will benefit the patient's recovery.
The Tools of Permanent Brachytherapy
LDR Brachytherapy seeds are about a quarter of an inch long and only as thick as the lead of a mechanical pencil. The radioactive seeds are actually titanium pellets filled with radioactive material. The body does not reject titanium, which is also used for joint replacements. The cases are either stranded seeds or free seeds, which are not attached to any other seed. Many researchers believe that using stranded seeds, which are brachytherapy seeds tied together with a suture, have a lower occurrence of migration out of the body or into the lungs.
The insides of the titanium casings are filled with one of two types of radioactive material: palladium-103 or iodine-125. Both materials emit low-energy x-rays that travel only a short distance, which keeps the radiation away from the prostate gland’s surrounding organs. While the low dose brachytherapy seed implants are permanent, their radioactivity is not. The seeds emit radiation continuously, usually over the period of a year.
Once the radioactive material has decayed, the seeds are no longer radioactive. Radioactivity is measured through half-life. Half-life indicates the amount of time it takes for half of the radioactive material to decay. Iodine-125, for example has a half life of 60 days. Sixty days after the seed implantation, only 1/2 of the original iodine is left. After 120 days, only 1/4 of the original amount is left. Once the radioactive
material has decayed, patients have only titanium casings in their prostate and their therapy has ended.
- Iodine – 125
Iodine-125 is a radioisotope that emits a low energy x-ray. Iodine-125 gives off energy at a slow and continuous rate. The half life of iodine is 60 days. The side effects of brachytherapy with iodine are less intense than those associated with use of palladium, however, these symptoms usually last longer. The energy of iodine also travels farther than the energy of palladium. Iodine therefore may pose a greater risk in irradiating surrounding healthy tissue, but a lower chance of cold spots, which are areas of insufficient radiation treatment.
- Palladium – 103
Palladium-103 is a radioisotope which emits very low-energy x-rays. Palladium gives off energy more quickly than iodine. The radioactive half-life of palladium is 17 days. Some patients as a result will experience more intense side effects that onset more quickly but that also go away faster. The radiation from palladium also does not travel as far as the energy from iodine. The result may be that the organs surrounding the prostate are less likely to be irradiated during treatment. Palladium, however, may result in more cold spots during treatment.
The Tools of Temporary Brachytherapy
HDR brachytherapy uses a seed that is sometimes called an iridium wire. In LDR brachytherapy, hollow needles plant the seeds. In HDR brachytherapy, thin plastic catheters, with diameters of about 1.9 millimeters are inserted into the prostate through a template. The iridium wire is inserted into these catheters one at a time then left in place for a few seconds.
Iridium-195 is a radioisotope which emits a slightly higher-energy x-ray than palladium or iodine. Iridium-195 has a half-life of 72 days. The iridium is left in the body for only a short time. Patients who undergo HDR brachytherapy will receive treatment with the iridium over a two day period. Radiation may be administered two to three times.