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ct vs. pet scan measurements


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Does anyone know if CT and pet scan measurements are comparable? My dad had ct 10/14, PET 10/31 and another CT 12/13. He has had two treatments of carboplatin/taxol. His oncologist is wanting to switch out chemo drugs based on measurements between ct #1 and CT #2 where a tumor on his liver is larger - but if you consider the Pet measurement vs ct #2 - the liver tumor is smaller (liver biopsy is non small cell adenocarcinoma). Of course we are not thinking fast enough in the doctor's office to consider this - today was a frustrating day it seemed like the oncologists office wasn't quite together. It was very busy maybe they were trying to see everyone before the holidays.

Thanks for any input.

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the PET is not an accurate measurement of size. there is a CT component to the PET, but it is not the same as the regular CT you get. just speaking from work experience where i know we would not look at a PET/CT as proof of change in a tumor size, we would require a dedicated CT to monitor tumor change/shrinkage/progression. you may want to ask dr west, but my work experience agrees with your drs take, that the information from the CTs are the more accurate measures. also, i would recommend you calling the dr and asking them, they should be happy to explain to you their thought process so you can decide for yourself if it seems acceptable.

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I have no firsthand knowledge, but can give you my Dad's Oncologist's opinion. I asked her if Dad's 1st follow-up would be PET or CT. She said CT as it gives her better data to use to track response. She uses PET to determine spread/activity not tumor size.

Sorry to hear that your Dad's initial response wasn't what you had hoped for. Hang in there!!


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CT is for measuring size and how it looks. A PET measures the metabolic activity.

In the past PET was not used to determine if tumor was responding to chemo. Recently I believe there has been studies that indicate PET can be used to measure response to chemo.

PET uses a measurement called SUV (Standardized uptake value). This measures the amount of uptake by tissue of the sugar.

A SUV of greater than 4 (may indicate a tumor)

I don't think you can compare CT to PET. It is like comparing apples to oranges.

You could compare PET#1 vs PET#2.

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