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Prostate disease and the
pharmaceutical industry
Prostate Cancer
Radioactive seed implants for prostate-confined disease
Brachytherapy will be considered in more detail, because
although it is a form of radiation therapy, the radioactive
‘seeds’ are more akin to a medicine and do not depend on large
machines to administer the radiation. Here, the radiation
is permanently placed inside the prostate, rather than applied
by an external machine.
The insertion of radioactive seeds of iodine (Iodine125)
seeds was first done by hand about 20 years ago and required
an operation to expose the prostate gland. The surgeon would
feel the gland with his fingers and decide where to place
the seeds. This was an inaccurate method and the seeds were
often not placed in the best position, resulting in some cancer
cells surviving and regrowing in later years.
This has now changed and new technology has taken over. Today,
the first step in this treatment is to make a very accurate
map of the shape of the prostate (a volume study). This is
done with a special ultrasound probe inserted into the rectum
which provides several pictures of the gland in cross section.
When reassembled, they give a picture of the prostate as a
whole and the position and shape of the tumour. The study
takes place under a short-acting anaesthetic in about 30 minutes
and is painless. From this map, the radiotherapist calculates
the number and position of seeds required, and the radiation
strength of each one. In this way, treatment is tailored to
the individual patient. The radioactive seeds themselves (Nycomed
Amersham) are made to order for each patient.
Customised seeds are necessary because the radioactivity
of the Iodine125 halves in intensity
every 59 days (the half-life), so the seeds cannot be stored.
Once made, the seeds are linked together into short strands
which are mounted into special hollow needles. The seeds are
then inserted by the surgeon under ultrasound guidance through
a special template. In this way, rows of radioactive seeds
(80-100 in total) can be placed very precisely into the prostate.
Within three or four days, people are ready to return to their
regular activities. Iodine125 is a very appropriate isotope,
because the radiation given out does not penetrate far into
the tissues surrounding the prostate, so there is minimal
damage to surrounding healthy organs. Also, the radiation
from the seeds rapidly declines and less than two per cent
of it will remain at the end of the first year. The ‘decayed’
seeds are left in permanently and cause no harm.
Experience with this method now extends to a follow-up after
treatment of up to 12 years. Some recent clinical trials show
that a higher percentage of people getting brachytherapy remain
free from disease than with either external beam radiotherapy
or radical prostatectomy. Also, the complication rates and
side effects are less severe in most people than with the
other two methods and there is less incontinence and impotence.
Several hospitals in the UK have now developed expertise in
this area.
Patient selection is quite important in brachytherapy and
the gland itself has to be reasonably small. If the prostate
is too large, medicines (LHRH agonists and/or antiandrogens)
can be used to cut off the supply of testosterone, which shrinks
the gland. This is successful in 90 to 95 per cent of people,
who can then undergo brachytherapy. This is very promising
data, but the method is not suitable for everyone, especially
men whose tumour has spread from the prostate and invaded
nearby organs. However, in a few such ‘at risk’ men, brachytherapy
can be combined with low-dose external beam radiotherapy,
with added beneficial results. If more distant metastases
are present, then neither brachytherapy nor surgery are appropriate
and anti-cancer medicines become the treatment of choice.
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