Frequently Asked Questions
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Q. How many other doctors have you trained in the seed implant
A. The Seattle Prostate Institute implant team now consists of 25 urologists and radiation oncologists trained here at the Institute in prostate seed implantation. The team meets monthly to discuss cases, improve the technique and improve our understanding of prostate cancer. The Seattle Prostate Institute (SPI) began a state-of-the-art training program here at Swedish Medical Center in March 1997 and have since trained over an additional 750 physicians, physicists and nurses. We are currently training physicians, physicists, dosimetrists, and nurses from the U.S. as well as around the world. In addition, SPI has hosted an annual Advanced Prostate Brachytherapy Symposium for experienced brachytherapists.
Q. What is Pubic Arch Interference and how do you test for
A. One important determination in deciding whether seed implantation can be technically performed is to evaluate the position and shape of the pubic arch. If the pubic bone, which is shaped like an upside down V or arch, is too narrow, it can be difficult or impossible to place needle in the prostate accurately and completely. SPI has developed an ultrasound pubic arch study that evaluates the position of the pubic bone at the time of the volume study. Occasionally we will also order a CT, which can also do this evaluation. Determining whether the pubic arch will prevent a good implant is obviously valuable. For those patients who have large glands and arch interference, shrinking the gland with hormonal therapy can often make the patient an implant candidate.
Q. Why will the patient have a CT scan soon after the
A. The CT scan is performed to confirm the placement of the seeds. The CT allows the implant team to do a post-treatment dose determination. The post implant dosimetry acts as a permanent record of the implant. It also gives the implant team another means of evaluating the quality of the implant. On very rare occasions, additional therapy may be suggested.
Q. What medications do you prescribe before and after the
A. Typically, an alpha-blocker (Flomax, Cardura or Hytrin) is prescribed prior to the procedure. These are medications that relax the internal urethral sphincter muscle, allowing for improved urination. Because it can take a few days with Cardura or Hytrin to reach a proper dose, it may be started several days prior to the procedure. After the procedure, patients typically continue the alpha-blocker for four weeks, longer if necessary. In addition, patients are given an antibiotic and an anti-inflammatory drug such as Aleve. The Aleve helps to reduce the normal swelling, improving the urine flow.
Q. What is the difference between palladium and iodine
A. Iodine and palladium seeds are nearly identical in their appearance. Both are 0.45 cm long (about the size of a grain of rice) and are implanted in the same way. Both emit low energy radiation. The primary difference between these two isotopes is the rate at which they give off their energy. Palladium gives up 90% of its energy within two months, while it takes approximately six months for iodine to release 90% of its energy. There are advantages to using both isotopes, which is described below in a related question. There is no proof that one seed is better or stronger than another. The doses and seed strengths, in fact, are prescribed to produce the same biologic effect. Often the choice will relate more to the physician’s preference and how they were trained and developed their clinical experience.
Q. What dose of radiation will each kind of seed give during its
A. It depends on whether the seed is used as implant alone or in conjunction with external beam. For an implant alone, Iodine delivers 145 Gray (14,500 rads) and Palladium 115 Gy (11,500 rads). When combined with external beam radiation, we can safely give a bit more than ½ the dose for each modality, yielding a very high anti-cancer dose of radiation. Iodine will deliver 110 Gy in this setting and Palladium 90 Gy. The exact definition of how dose is defined has evolved over the years, however this is essentially the same biologic dose we have delivered throughout our brachytherapy experience.
Q. What is half-life? How long will each kind of seed be radioactive
A. Half-life describes the time in which an isotope loses half of its strength. For example, iodine, which has a half-life of 60 days, will be half of its strength at 60 days. 60 days later it will be half of this strength. It takes about six months for iodine to be at about 10% of its original strength, and a year to lose effectively all of it. Palladium has a half-life of 17 days. Within two months it has given up 90% of its energy and has lost almost all of it by six months. Again, there are advantages to both isotopes. Palladium gives up its energy quicker but this does not mean that it is necessarily better or stronger.
Q. How does radiation from seed implantation kill cancer cells? Are
there forms of prostate cancer cells that will not be affected by seed
implantation radiation? How will the radiation from seed implantation affect
healthy cells in the patient's prostate?
A. There are entire books written on radiation biology and why radiation works. Briefly though, Radiation damages DNA, RNA, and proteins of cells but primarily causes cancer cell death through direct DNA damage. DNA is the instruction manual for a cell to replicate. Cancer cells don't die immediately after radiation. When the cell initiates a replication cycle and tries to divide into two cells, the DNA breaks prevents the cancer cell from dividing properly. The cell ultimately dies. Since prostate cancer cells often divide slowly, the cancer cell may not die for months after the implant. This is why it sometimes takes a long time for the PSA to drop to low levels. Since the cancer cells are most sensitive to radiation at the time of division, it is necessary for cure to have radiation present when this occurs. This is one of the reasons why ‘fractionating’ external beam radiation is advantageous (the other reason is that it allows normal cells to repair). All cells are sensitive to radiation. Because of the high dose, some normal prostate cells die as result of the implant radiation. Some normal cells remain however, which explains why PSA is still present years later. Normal cells can repair the DNA damage caused by radiation due to specific repair enzymes often lacking in cancer cells. The result of the healthy cells dying is that the prostate function of producing prostatic fluid for ejaculation may be substantially reduced. The presence or absence of an ejaculate, however, does not reflect whether the cancer is cured or not.
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