PET scanning in stomach cancer patients is used to detect secondary tumors in people who are thought to have, but not confirmed, disseminated disease.
It can also be used to check for response to treatment.
Often abnormalities are picked up on CT staging scans that can’t be confirmed as a tumor due to size or perhaps a non-diagnostic appearance.
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This is a nuclear medicine scan that involves the injection of FDG or Flurodeoxyglucose, a sugar derivative that is taken up by cells as an energy requirement.
Whilst it is taken up by all cells, tumor cells divide faster and require larger amounts as a consequence.
As the cells use up the FDG, it is fixed in the cell by a process called phosphorylation which in turn fixes it within the cells.
Because it is radioactively labelled, radioactive decay occurs and emits radiation. It is this radiation that is measured and displayed as an image.
The time it takes to do you scan varies, but can be anything from 20 minutes to 2 hours.
The results of the scan are compared to images already taken with CT imaging.
Sometimes, PET-CT imaging is used, where a CT scan is taken at the same time.
This has the advantage of allowing the radiologist to concentrate on abnormal areas picked up by the scan imaging.
You will get your results once the scans have been reported by the radiologist and sent to your doctor.
Like any test there are always limitations. These include:
1) False positive results – misinterpretation of an abnormal area by the radiologist
2) Some stomach tumors don’t take up FDG well therefore providing falsely negative results (particularly poorly differentiated adenocarcinomas, mucinous and signet-ring carcinomas).
3) Difficulty distinguishing a primary malignancy from a primary with local lymph node mass if in close proximity
The amount of radiation exposure you get from a scan is about 8 millisieverts or approximately 400 chest x-rays worth of radiation.
This may sound a lot, but is very small in comparison to the amount of radiation you might have to treat this disease.
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