Facts about Radioactive Seed Implants (Prostate
brachytherapy)
The purpose of this web page is to explain the details of radioactive
seed implants for prostate cancer.
 Prostate Brachytherapy or Radioactive Seed Implants consist of a radioactive
source inside a with titanium shell. One seed is about the size of a grain
of rice (see photo). One of two radioactive sources is used - Iodine (I-125)
or Palladium (Pd-103). Both radioisotopes emit very low energy radiation,
which is primarily absorbed in the treatment area or "target"
tissue immediately surrounding the seed.
Anywhere from 40 to 130 seeds may be implanted throughout the entire
prostate. The calculated volume of the prostate determines the exact number.
The seeds remain permanently in place. However, they gradually lose their
radioactivity over a period of time - Iodine seeds over a period of about
six months and Palladium seeds over a period of about three months. The
following graphs illustrate this process.
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Percentage of Radioactivity Remaining After Time
For a larger view, Click Here |
The appropriate treatment for prostate cancer depends upon whether: 1)
it is localized to the gland, 2) locally advanced, or 3) spread beyond the
gland. Once a diagnosis has been made (usually by transrectal ultrasound
guided biopsy), the presence or absence of cancer elsewhere in the body
must be established.
Other features of the cancer such as the appearance under the microscope
(e.g., grade and Gleason score), prostate specific antigen (PSA) level and
the physical examination, can play a role and help to predict the likelihood
that the cancer is indeed confined to the gland. Organ-confined prostate
cancer can be effectively treated with surgery, 3-dimensional conformal
radiation therapy or prostate brachytherapy (radioactive seed implant).
These are general guidelines and each treatment is individualized to each
patient.
History of prostate brachytherapy (radioactive seed
implant)
The use of radioactive seed implants for prostate cancer is not new.
This technique has long held promise as a method of delivering a very high
dose of radiation to the prostate while simultaneously reducing the amount
of radiation to the adjacent organs such as the bladder or the rectum. Early
efforts in the 1970s and 80s were limited by a lack of effective technology
to place seeds in the prostate. As a result, the distribution of seeds in
the prostate was inadequate to provide an even dosage of radiation to the
entire gland. The results were suboptimal and this method was largely abandoned
in this country.
As the technology for medical imaging improved, efficient and effective
means of planning and monitoring the placement of seeds were developed.
The most widely used have been transrectal ultrasound guidance and CAT Scan
(Computerized Axial Tomography) planning. The ability to accurately plan
seed placement and verify seed position has led to a renaissance of the
implant technique. Another advantage of modern implant techniques is the
avoidance of surgery: the seeds are placed in the prostate by needles through
the perineal skin (the area of the body between the scrotum and the rectum
between the legs) under anesthesia in an operating room environment.
For more information, please refer to our Frequently
Asked Questions
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