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.