I wasn't sure where to ask this question but I decided to write it under Treatment. What is the difference of the 2 types of test? What can a pet scan see that the CT Scan could not see? A pet scan is about Php150,000 or $3,750. For checking the spread or mets of the cancer, what is more exact?

Note: Joyce never had a Pet Scan due to cost. Would there be a huge impact on her treatment and diagnosis in the past? present?

Ina, Im sorry but I dont know the exact differences between the PET and CT scans. But I do know a little about them and will attempt to help you with some info. PET scans are known to give false positives and are very expensive. From what I understand a CT scan is a good alternative to the PET without the false positives (much less cost too).

Hi Ina,
I am not a doctor, so please take this with a grain of salt, but I am a scientist who does imaging for living (in my case MRI), so I am a bit informed about the topic.

CT/CAT scans are basically fancy versions of X-ray imaging. CT stands for computed tomography. X-rays are used to make a three-dimensional anatomical image of the body area in question. Cancers can be detected by the swelling and anatomical distortion they cause, or by surrounding edema.

PET( positron emission tomography)is based on detecting pairs of gamma rays emitted indirectly by a radioactive biologically active contrast agent introduced into a body.
**( Technically, the contrast agent/tracer is unstable, decays by emitting a positron, which happens to be a particle that is anti-electron. When positron meets an electron in the tissue after traveling a little they annihilate emitting a pair of gamma rays, and an 3-D image can me made to show the origin of where those gamma-rays)**.
PET is used to detect areas of high metabolic activity in the body. It typically uses a molecule called FDG, an analogue of glucose. All the cells in our body use glucose for their metabolism, but some use more than normal. This can be perfectly normal, for example, our brain, which constantly uses a lot of energy. Also, cancers use more energy then normal cells, so this is how they are detected.
The radioactive dose one receives is very small so there is no need to worry. PET is pretty good at detecting metastases around the body, as well as primary cancers. It can not detect very small cancers.
PET suffers from poor resolution so sometimes when they do PET they will do a PET/CT, use CT images for anatomy and overlay PET ones on the top to show activity.

So, to summarize, CT will show if something looks bigger/has swollen etc (anatomy). PET will show if it has a high metabolic activity (function). The can be complimentary. Either of those can be indication of cancer, but doesn't have to be, things can be swollen/have higher activity and not be cancer. Biopsy is the only way to tell if something is cancer or not. Images tell us where to look.

In my case, I had both CT and PET/CT done. CT has detected my primary tumor but nothing in the lymph nodes in the neck as they were all the normal size/not swollen. PET, on the other hand, has in addition to the primary tumor, also detected activity in the lymph node area. After surgery, one of the removed nodes, pretty small one, 7mm, was positive for cancer.

Amazing info. Thanks for sharing it.
Prayers for you as you begin your journey with radiation. No chemo?
Kathy

You are very welcome Kathy, hope it is helpful and not too technical.
Thank you for your prayers. No chemo indeed, my RO said no MO would ever even touch me at this point. Here is to hoping they are right and I will never need it.

Ina,
in my husband's case, the CT did not pick up the primary, only the enlarged lymph node. The PET/CT did pick up the primary, as well a little activity in a second lymph node. So in our case, the CT was a false negative for the primary.

I think the question to as in Joyce's case, is what would the doctors do with the additional information, and would it lead to an improved chance of cure or better quality of life. Of course, Joyce and the family would need to ask themselves a similar questions - for some, having a more definitive result (good or bad) is better than having less information.

I just lost my dad to congestive heart failure this spring, and my thoughts are with you and yours in this difficult time. Please remember that, as much as we wish, we cannot always give health and youth back to our parents. We can give love and care, and you are doing this as much as is humanly possible.

Maria