Home Forums Melanoma Diagnosis: Stage IV CT vs PETct

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    Me again :)

    My wife’s on her 3rd month of the BRAF/MEK combi and in the beginning of Octover she will get her 3rd CT scan (first was on June 3rd, second on August 1st).

    We also see a doctor in Brussels who has access to Pembo (only 5 locations in Belgium at the moment) and he would like to perform a PET CT scan because he can get more info (I forgot what exactly) from a PET scan.

    For continuity of the scans our primary doctor still wants to run the 3rd regular CT scan.

    Couple of questions….

    – Does it make sense to do both (in October as planned) – what extra info will we get from the PET-CT? So is it worth doing it? Or the other way around, if we only do the PET scan, do we need the regular CT scan?

    – What’s the impact on the body? We’re aiming to boost my wife’s immune system through healthy eating and supplements – will we undo this via all the scans and fluids she needs to take?

    Thanks for your advice,



    I think you just need to decide with your oncologist what the plan is.

    Due to my active tumor growth, at one time I was getting 4 (body) PET CTs per year. At this point we do 2 per year. So over the course now of several years I can see why diagnostically, a PET CT is superior. My oncologist always goes over the path report, and compares it that to the actual images from whatever scan is current, and the previous scan. You always want to know what has changed from one scan to the next. I like looking at the images…

    With my 4th Brain MET, that MET did show up in the Brain CT. They did a Brain MRI anyway.

    On my 5th Brain MET it would NOT have showed up on a Brain CT, just too small is what I was told.

    Guess I don’t have a straight up answer.



    Hey Rick,

    My understanding of CT vs. Pets is that CTs have better resolution. It seems to be the standard for all trials since the doctors can get a more precise measurement of the disease and therefore track the progress of the disease better. Even though CT’s have better resolution, it seems Pets can sometimes be better at finding disease. This was true for me when I had disease in my small intestines and the CT did not find it but the Pet did. For the Pet scans, as you probably know, they inject you with some nuclear type glucose. Cancer seems to really “suck” up the glucose which causes a “glow” to appear on the pet scan images. I think one thing you can discern from Pets that you can’t from CTs is the metabolic activity of the disease. I had a Pet scan several months ago which revealed that my stable tumors had no FDG uptake (they weren’t “sucking” up the glucose). They could see the tumors on the pet image but they weren’t glowing. This was obviously great news and something I would not have known with just a CT.

    As far as doing both and the toxicities involved that is something I would talk to my doctors about. Personally I’d be reluctant to do both without at least 2 or 3 weeks between them or maybe even 4 weeks. I would think that the Pets would be a little more toxic than the CTs but I don’t know that for sure. It just makes sense to me that they would be. Also I’ve heard Pets are more expensive and sometimes harder to get insurance to approve them.



    Brian pretty much summed it up, but I had this mostly written already when I saw his post, so figured I’d and my own two cents…

    CT scans use a computer to combine multiple x-ray “slices” into sort of a 3D x-ray, showing the shape and structure of organs, bones, tumors, etc. More accurate CT scans use narrower slices and higher power x-rays. The key about the diagnostic capability of a CT scan is that it shows structure.

    A PET scan uses a radioactive glucose, injected about an hour before the scan, that shows metabolic activity, with the understanding that cancer cells consume glucose (sugar) more quickly than most normal cells. More active areas will “light up” more brightly than less active areas. A PET scan alone would show a collection of colored “blobs” with some difficulty correlating a bright spot to a specific body part. For this reason, a PET scan is done with a low-power CT scan with the images then merged via computer to map the PET results onto an image of the underlying body structures.

    There is no perfect type of scan and often a positive finding on one scan will result in a follow-up with another kind of scan. For example, PET is notorious for false positives and certain organs, like the brain, naturally consume more glucose, so will always light up brightly, with only larger tumors being seen by a trained radiologist. Also, inflammation or injury unrelated to cancer will often light up on a PET scan. On every PET/CT I’ve had, it always notes that the CT portion is low power and should not be used alone for diagnostic purposes (although there have been instances where we’ve seen obvious things on the CT portion that my doctors have used diagnostically).

    From others’ posts, I’ve seen that some facilities rely on PET/CT for regular monitoring and others rely on CT, then using the other scans, also including MRI, for follow-up. My original monitoring protocol was a neck-to-pelvis CT every three months, along with a shoulder MRI of a specific bone lesion. However, after finding a new bone lesion on my shin bone (well below the scanned area for the CT), I now have a full-body PET/CT every three months with a handful of CT scans or MRIs as follow-ups. I also had an annual brain MRI, until I had a brain tumor, and now it’s every three months, too. As a matter of comparison, a full-body PET/CT for me takes about 40 minutes (plus an hour beforehand while the glucose is allowed to be taken up), a chest-to-pelvis CT in only a couple of minutes, and an MRI for a specific body part (brain, knee, or shoulder) can take 45-60


    Comparing the radiation dosage of each is a challenge and can depend on the machine being used, how large an area is being scanned, among other factors. If you search the Internet, you should be able to find some approximate comparisons, though, and as Brian said, worthy of a discussion with your doctor.

    I hope that helps,



    Thanks for all the info, greatly appreciated!

    For now we’ve decided to go for the PET as we’ve never had one and our oncologist does value the extra reads it give. We won’t do the CT at the same time for toxicity reasons but will probably fall back on this apparently more accurate analysis, to track progress (or better: reduction) over time, from now on.

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