Hi,

This is about a scan called PET (I'm not sure what it stands for) that is supposed to differentiate cancer cells from normal with an accuracy higher than any other scan system available (they say accuracy is higher than 95 percent). Have any of you used/heard of this being used? This just became available in India and we are thinking about using it if needed (for an 8-wk-post-rx scan to determine the nature of a lymph node that's still persisting).

Ashwin.

Ashwin,

I had a PET scan and an MRI to look at how I was doing three months after treatment. MY ENT made very clear to me that the PET scan, by itself, was likely to show a lot of "false positives" in terms of showing up spots that were still healing as being indistinguishable from spots where there could be cancer, which is why I also had the MRI. He also said three months after treatment was the earliest he would use a PET scan because it is very sensitive but also overly sensitive and picks up spots that are inflamed and irritated by treatment but not new cancer.

If this equipment is relatively new in India, I'd hope you could find someone familiar with these issues to interpret the PET scan for you so you don't get needlessly worried.

Nelie

PET scans are done by first giving an IV of glucose that has a radioactive marker. Cancer cells have a higher uptake of sugar than regular cells so it tends to concentrate the radiation which is then read by the scanner. It is a long scan and painless. The accuracy is enhanced if combined with CT. If you are healing from radiation and/or surgery there is a possibility of more false positives where healing is taking place. All scan modalities have a certain degree of false positives and are never used as a single diagnostic tool, merely an adjunct to the biopsy, palpation exam, nasolarynoscope, MRI, blood work, tumor markers, CT and mirrors.

PET/CT's have shown reading up to 98% accuracy. PET alone is a little lower.

Most of us have had PET scans for the original workup. Some have regular PET scans as part of their follow-up protocol.

The other important factor in PET/CT (positron emmission tomography) scans is that ongoing scans are always compared to a benchmark scan shortly after treatment to pinpoint areas that are increasing in size as well.

I saw a study in a 2004 Journal of Otolaryngology with results of 100% accuracy relative to false negatives.

Ed

I had a PET scan and it was good confirmation that my cancer did not spread and it was contained to my tonsils. Again as the others of said its a nother view of things that help determine the treatment or condition.

A test which finds all kinds of things, disease or not will have a very high number if you are looking at false negatives.... the problem is specificity. When you are looking for a particular "trait" of a disease and not the disease itself as in PET scans, the problem is not false negatives, it is a high degree of false positives. Gary has this right and it has been stated here before. Scanning technologies are only part of the puzzle when it comes to knowing what is going on for sure.

Just a note I would add in agreement with Ed's comment and in particular to head and neck cancer. When diagnosing, a PET scan does have issues with false positives because of the uniqueness of the way that the salivary and swallowing functions occur.

The doctor explained that unlike most any other part of the body, the functions that are happening in our mouths an throats cause the cells to burn more energy thereby uptaking a more significant amount of glucose than cells in other parts of the body. Because the PET scan is looking for the rapid uptake of glucose it will sometimes show bright areas in the head and neck region that are not cancerous but that appear on the scans because of the normal functions of this part of the body.

This goes in line with why the docs must wait for a significant period of time after treatment to do these tests since the treatments can also cause the cells to become hyperactive with glucose intake and the readings are not of much value.

Ultimately I must agree with Brian. There is not a single test or tool that can tell you everything you need to know. It is the old whole is the sum of its parts routine. By using multiple tests that have their individual advantages, the docs can get a fuller and clearer picture and that is the best way to tackle cancer in my opinion.

Harry is going for his second PET scan (first since completing treatment) and they will do a CTscan as well. They also do regular blood tests and then the doctor puts all of this information together to determine if things are rolling along fine or if something needs to be addressed.

Harry said once that while he hates doing so many tests he finds a peace of mind that they are getting the whole picture the more they do so he does them all.

Good Luck!

Cindy

I believe the true value of the PET is to screen for Mets to other areas. There is a lot going on in the H and N area.