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Prostate HDR Brachytherapy Implant Tecnique
This page may be more technical
or graphic than some would like to see. However, many people ask us
for these details so we thought it would be beneficial to describe
on the webpage. Please be aware that other centers may have very different
techniques, and also that we may modify our own technique from time to
time.
The Implant Procedure
On the day before the implant, the patient will take a bowel-preparation drink to empty out their bowels. On the implant day, the anesthesiologist may place an epidural catheter.
The
patient is brought into the OR suite and usually placed under general
anesthetic. The legs are placed
up into stirrups, the skin is cleaned with an anti-septic solution, and
the legs are draped in sterile gowns.
Next,
we take our B&K rectal ultrasound probe, and insert it into the rectum.
It is attached to a "cradle" device so that we do not have
to hold the ultrasound during the procedure. A 3 inch square template
is attached to the ultrasound. This template has holes every 0.5 cm (~1/4
inch) through which we will place the needles.
The
rectal ultrasound is moved until we see a nice image of the prostate
gland on the monitor.
Then, under ultrasound visualization, we inject three non-radioactive
gold seeds into the the prostate gland. These
will
serve as reference markers when we do a CT scan later on, and they
will also be very helpful during the external beam radiation to ensure
daily set up accuracy. The
ultrasound will also guide us during the placement of catheters. As each
catheter is placed it shows up as a bright white spot on the ultrasound.
Now,
we begin inserting needles. We use "flexi-guide catheters" which
are hollow plastic needles with a removable metal insert. They are 23.5
cm long and 2 mm wide (9 inches long and ~1/16 inch wide). These are
placed through the template, through the skin, and into the prostate
gland. They enter the skin below the scrotum and above the rectum. As
these needles are being placed into the prostate gland, we are able to
see where they are going on the ultrasound monitor. Our goal is to generally
put two rows of needles along the sides and bottom of the prostate gland.
We do not place any needles in the center of the prostate, where the
urethra (urine passage) lies. We will use anywhere from 15 to 30 needles,
usually around 20, depending on how large the prostate is.
Next, we remove the rectal ultrasound and cradle, and separate the blue template from the cradle and suture it onto the skin.
The
urologist now inserts a flexible cystoscopy through the penis and into
the bladder. The legs
are lowered
down, so that they are level with the rest of the body. The radiation
oncologist pushes in each of the flexiguide catheters one by one, until
we can see "tenting" of the bladder lining through the cystoscopy.
This tells us that these plastic needles are pushed in all the way
through
the prostate gland, but not actually into the bladder.
The cystoscope is removed, and a foley urinary catheter is placed.
The patient is woken up, transferred to another bed and brought to
the recovery
room. He will stay there for about 1 1/2 hours until it is time to
go for the CT scan.
The CT scan and CT based dosimetry
The CT scan is critical for our dose planning. With the CT scan, we can see where every catheter is in relation to the prostate gland. The computer can then determine how much radiation each of the needles should receive. If a needle is too close to the urethra or the rectum, it may receive no radiation. If a needle passes directly through the center of the tumor, we will give that needle more radiation. This whole process is known as "optimization" of the dose distribution.
We
start in the CT scanner with a lateral scout view, which looks like a
regular x-ray. On this picture you can see the bladder, which looks white
because of contrast dye. You can also see all the flexiguide catheters
coming right up to the bladder. Next, the CT scanner will take a series
of "slices" through the prostate gland. At this step, we can
push some of the needles in, or pull them out a little if we are not
happy with their positioning. We can also add a needle if necessary.The radiation oncologist next outlines the prostate contour on each CT slice on the computer screen (red circle).
We
will add an extra margin on the left side or right side if we feel there
is a risk of extra-capsular spread there. If possible, we will outline
where we believe the tumor likely is in the prostate gland so that
extra dose can be given there (blue circle). Tumor location is estimated
based on MRI scan, biopsy, and physical exam. Our physicist or dosimetrist
next takes the films and digitizes all this information into the Nucletron
treatment
planning computer. The computer calculates how much radiation each catheter
should receive. We then manually "tweak" some of the catheter doses
to assure a low dose in the urethra and rectum, and a high dose in the
area
where
we feel the cancer is present.The catheters are hooked up to the brachytherapy machine three times over the following 24 hours,
for
a total of three treatment fractions. Our prescribed brachytherapy dose
is often 600-650 cGy per fraction, for a total of 1800-1950 cGy. However,
the peripheral zones of the prostate gland will receive a higher dose
that
this, and the area where
the tumor is will often get about 120% or more if possible. This radiation
dose is very powerful radiobiologically because it is given over treatments
of only a few minutes in duration.HDR Treatments
The
patient stays in a hospital bed during those 24 hours, but is brought
down to the radiation oncology department three times to have the catheters
connected to the HDR remote afterloading unit. The catheters are connected
to transfer cables, which plug into the HDR unit. Each treatment takes
about 10 minutes and is totally painless. The HDR unit
pushes
a single
radioactive
pellet into each catheter one by one, for a precisely controlled amount
of time. The pellet rests along those portions
of the catheters that are in the prostate gland. The only time there
is
any
radioactivity present is during those three 10 minute treatments. The
patient is not radioactive at anytime while in his hospital room, or
while at home. There is never any radiation exposure to family or to
hospital staff.
After the third treatment fraction, the catheters are pulled out. The
patient is discharged from hospital within a few hours, and can resume
normal activities very quickly. Generally, taking a couple days off work
is encouraged.
External beam radiation will begin 1 - 3 weeks later.
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