How Accurate is a PET Scan?

NewHere said:

No Idea

I had a bone scan the day before the MRI that showed I was probably lit up with our buddy.

The bone scan was clear and I was psyched.

Whoops.

And the other scans were off.

PET scans are suppossed to be good.  But I am in a bit of a cynical mood right now.  Waiting for my scan results.  And thinking about kicking my Oncologist to the curb becuase of the staff and the response I had about 9 months ago where they treated me like s--t.  And realized the oncologist was phoning this in also.  It was obvious he was not paying jack all to the report.  There was no way he could come in and say what he did.

Bottom line JJ, get your answers and do not let people mess with you.  I truly think, sometimes, that we all care a ton more.  Grill them until you get the answers.  If they do not answer to get you to the point where you are happy with them being precise and answering you.  Press them more.

I am really kind of mad tonight realizing some things, so take my points right now with that in mind.  

I got s---ed on the colonscopy the other week, should not have been released and got messed up.

Get your answers.

Again I apologize for being kind of cranky.  But we all need to get the answers and treatment we deserve.  Everyone here is tough and no whining or complaining.  Do not let them do this to you.  (Or us.)

xoxo

I had a real jerk for an oncologist initially.  The hospital just assigned him to me. I ultimately fired him and got the onc of my choice.  She was a real gem.  Since you pay the bills, you are hiring these people.  If you don't like someone, or feel they are not doing what's best for you, replace them!!  Best of luck to you!

John23 said:

Pets and cats

Pets and cats

The PET was originally designed as a way to better outline a tumor for surgical needs. The principal is simple: An active cancer tumor will generally use more glucose than surrounding good, healthy cells. By using radioactive glucose, the active cancer cell should theoretically uptake more radioactive glucose and "light up" on the scanned area while the healthy normal cells remain dark(er).

Of course, using the PET for a "treasure hunt" has become the norm, with the dialog indicating that "if it lights up, it's cancer" and the need for chemical therapy.

What they don't tell you, is that any cell that is in the process of repair, in the healing process, or in the new growth process will light up. Anything that will cause a good cell to use more glucose than normal will show up on the scan.

If a cancer cell is among cells that are growing faster than it, it will not "light up", and is one reason that metastases is a problem; a slow growing cancer cell cluster that settles in a faster cell growing area won't be detected until it's a good sized tumor.

While the PET is a fine invention, it is not the answer to much. False readings are frequent. But most Oncologists and physicians seem to feel that regardless of a false positive it's better to be "safe that sorry" and load the toxins in "just to be safe". (and at 10~20 grand a shot, why not?) (</cynicism>).

Even without a scan or indication of cancer, there lately seems to be a major push to administer Chemicals and radiation regardless. The PET can bolster their argument, but a clean report never seems to detract from their argument.

We should always be aware of our options and the pitfalls of bad therapy and always, always, always, be our own advocate. Learn as much as you can; know some of the answers before you ask the questions and judge your physician based on factual information.

They're only human, you know......

Be well,

John

While the general message of your post is correct, it's an over simplification of one of the tools used by doctors to determine if a particular spot is cancer or not.  PETs are done with CT and the two are usually compared with each other.  There's a also person's medical history which factors in to whether one would think a spot is cancer or even if a scan would be ordered.  The lit up of regions is correct in terms of the concentration of radioactivity from the radioactive glucose injected into one's body.  This light up can be quantified and is measured in SUV.  The higher the SUV the higher the concentration of radioactive glucose.  The concentration of radioactive glucose is a function of cellular metabolism.

A radiologist would look at the shape of any lesion or spot on the CT in comparison with the lit up areas of a PET scan.  Tumors do have a particular shape which a radiologist can pick up on; along with how dark or light a region is on a CT indicating hypo/hyper density.  In addition, there are other diagnostic tools such as MRIs which can be used depending on the situation.  And trending of a particular lesion or spot is usually done along with blood work such as CEA.  This is why some cancer patients have scans done at certain intervals to see if there is growth (or shrinkage in the case of if someone is under active chemo treatment).  Plus a biopsy can be ordered to be more definitive.

In my case, I had two 3 cm sized lesions in my liver at diagnosis.  The radiology report did not state whether these were metastasis or hemangiomas.  The radiologist just suggested further investigation due to my prior history which was a large growth (tumor) found in my colon during a colonoscopy the day prior.  This is why you fill out on the form why you're getting a scan so the radiologist has a frame of reference on how to react to certain things he/she sees on your scans.  It's also part of the doctor's scan orders as to why the scan was ordered.  Because of the tumor in my colon, a PET/CT was ordered to see if the two regions would light up.  They didn't.  But the liver specialist I consulted still wanted to be sure as there can be false positives and negatives.  So he was there the day I had my colon resection.  He performed a biopsy of the two lesions which were quickly processed by the pathology lab to determine if he had to do a liver resection before my CRC surgeon did his work.  The results of the biopsy were negative for cancer so these spots were deemed hemangiomas.  Since then, each subsequent scan I've had has shown no significant change in those two lesions which further reinforces the diagnosis of hemangiomas.

So it's an over simplification to say if you have a spot which lights up on a PET, SUV uptake greater than about 3, your doctors are going to automatically order (more) chemo.  

Jan, my second Pet scan, in the middle of the chemo regime, lit up a node under each armpit, and one on my neck. As I had said in a previous thread, the Onc was bewildered [muttering "two cancers?"], and I was just scared. He was a nice old guy who told great stories, but he didn't mention that PET's have a fair amount of false positives. I had to go home, get online, and read about them to get some kind of reassurance, thank's for nothing Doc............................Dave

Jan,

When my wife was ill i got copies of the PET/CT scans on CD and poured over them at home along with copies of the reports.  The reports didn't match what I saw - spots in the lungs were not mentioned.    I asked a second radiologist to review the images and his report suggested possible lung mets as well as a tumor in the spleen, which was not mentioned in the first report.   I talked to both of them, the first was an oncologists turned radiologist and he assured me that the the lung nodules were likely not cancer.  Later he was proven wrong.  There is a real issue about  certainty in reading the scans and experienced radiologists will have different opinions.  And by the way, your family doctor probably just read the report, which is why he agreed.   A regular phycision has zero experience in interepreting a PET scan, and I doubt he look at it.  Also, my wife always got a combination PET/CT scan as they provide more information than a CT or PET scan on their own - something you might discuss with your oncologist.  You might also consider having a second radiologist render a second opinion on all of your scans.  It gets more complicated this way but if differences in opinions crop up they can be focused on and hopfully resolved, and where they agree you can have more certainty.

Peter