Part
of IPCSG presentation by OB-Ron, April 21, 2012
Tidbits
about C11-Acetate PET/CT and Clinical Trial in Phoenix
Dr.
Almeida, at the May 2012 IPCSG meeting, will cover the details of the
C11-Acetate PET/CT scanning and imaging technology for prostate cancer, and the clinical
trial. Here are some tidbits that I have learned:
The
clinical-trial (http://clinicaltrials.gov/ct2/show/NCT01304485)
started in April, 2011, and expects to run for a few years.
The
PET scans detect the unusual cellular metabolic activity
characteristic of cancer, providing superior selectivity than many
other scans (a low false positive rate).
They
can even detect early metabolic activity of cancer in bone,
providing detection much sooner than a conventional bone scan.
C11-Acetate
is a radioisotope tagged nutrient that prostate cancer cells take up
to feed their growth. The PET scanner detects the positron
emissions from it. The CT scan, done in tandem to the PET scan,
provides the anatomical information, so that when the two images are
fused together, you can see where the PET detections are located in
the body. Dr. Almeida told me he's getting better images than the
University of Kansas because of better technology – a recent model
machine that allows both lower CT radiation and lower amounts of the
radioactive tracers than used with some other studies.
The
scan covers from just below the pelvis up to just below the eye
sockets. With the larger scan area, no evidence of wide-spread
metastasis can give confidence to do focal treatment. Special
Prostate MRI scans usually only cover a much smaller region, perhaps
just the pelvis, and some special portions of the scan may be only a
small targeted region within the pelvis.
Some
organs and parts of the body concentrate the C11-Acetate naturally,
making tumor detection difficult in those regions, but prostate
cancer occurring in those areas is rare.
An
important early statistic from the trial is that about 70% of the
time, they are finding PCa disease beyond what conventional
prostate-bed salvage radiation treats. I think that explains why
the current standard-of-care fails so often.
The
tumors or lesions need to be of sufficient size and activity for the
PET scanner to show abnormal activity, which is why a PSA of greater
than 0.5 and rising is suggested, but I believe this is similarly
true for other advanced scans. This, of course, means small
colonies of cancer won't show up.
This
is a big question with recurrent prostate cancer. How often does it
stay in one location, not spread to many? It's a hope of the
clinical trial to get results from men who choose focal treatments,
to see how often PSA goes negligible and perhaps stays in remission
for a long time.
Short
PSA doubling time, indicating high activity, may enhance the
probability of detection. Studying how PSA kinetics relates to
probability of detection, when to pull the trigger on doing a scan,
is part of the study's goals.
Dr.
Almeida can give you probability of detection under various
conditions, but for me in December, he estimated an 80% chance of
detecting something when my PSA was 1.17 and rising rapidly. The
results might be better now.
Carbon
11 has only a 20 minute half-life, in contrast to a 110 minute
half-life of Flourine 18 used in a common FDG PET scan for many
other kinds of cancer. Thus C11 is safer for patients, causing
less total radiation load, estimated to be equivalent to about 1/3
of the CT scan.
The
20 minute half-life of C11 makes the scan much more difficult to
provide. The scanning center in Phoenix has a cyclotron in the
building next door so that they can produce the C11-Acetate shortly
before the scan, and quickly infuse it into you. The scan commences
after just a five minute wait for the cancer to ingest and
concentrate the C11-Acetate. The scan period, when you need to lie
still, takes about twenty minutes to complete. The radiation
diminishes so fast that there isn't time to transport the
C11-Acetate any significant distance to other PET centers.
Most
prostate cancer doesn't take up FDG (a type of glucose) as much as
most other kinds of cancer. Also, the FDG shows up more in the
urinary tract and might mask detections. For those reasons, the
conventional FDG PET scan doesn't work well with prostate cancer.
C11-Acetate or Choline do work well, and have been researched and
used in parts of Europe for many years.
The
clinical trial isn't free. The price is $3,000 because the scan is
very expensive to do and everyone in the trial is getting the same
scan and receiving significant benefit. The Mayo Clinic's price for
their C11-Choline PET scan is more than $7,000.
Dr
Almeida's goal is not only to get the PET scan FDA approved, but
also to convince Medicare and insurance companies that this should
be a new covered standard-of-care.
Recently,
Dr. Almeida has started a new clinical trial
(http://clinicaltrials.gov/ct2/show/NCT01530269) that includes newly
diagnosed men deemed to be at intermediate to high risk of
recurrence or metastatic disease. PSA above 10, or Gleason 7 or
above, or evidence of possible spread beyond the prostate qualifies.
This could be very valuable to guide treatment planning for these
men -- maybe avoiding recurrence or long term testosterone
deprivation therapy.
One
very important thing to know is that for a PET scan to work, since
it's reading the unusual metabolic activity of cancer, your cancer
needs to be active, growing, producing a rising PSA. That means you
usually can't be on a hormonal blockade like Lupron. When advanced
cases are diagnosed, doctors will often recommend some form of
hormonal blockade immediately. We need to teach these doctors that
they need to think differently, and suggest considering a scan
first.
If
you are on intermittent hormonal blockade (androgen deprivation)
therapy, you may be able to delay your next drug injection until the
PSA is rising some, then get the scan, and go back on the drug
afterward. Dr. Almeida told me that he has already tested
a few men in exactly that way. Imagine, if the scan finds specific
targets that can be treated, you might be able to get off androgen
deprivation, anti-hormonal, or other systemic treatment that is
giving you a lot of side effects. Isn't that worth thinking about?
The
Arizona Molecular Imaging Center is in an industrial park just a
couple blocks from the freeway. There are many nearby hotels. It
might be necessary to be there more than one day if your C11-Acetate
doesn't pass quality control tests, and they have to try again.
