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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 only if the stay will benefit
the patients 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. 60 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
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.
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