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PET Scan Versus CT Scan

PET Scan Versus CT Scan

Posted By
4/10/2019 11:48am
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Replies: 10

can anyone tell me the difference between a pet scan and a CT scan.  Which is best to use to detect Melanoma.

During my treatments I have had three of each in the last year.  all were neg. 

Just courious why some go pet and some to ct.



mrsaxde - (4/10/2019 - 12:26pm)

A PET detects radioactive decay from the radioactive sugar they inject you with. Cancer cells use sugar at a much greater rate than regular cells, and the scanner picks that up. A CT is at the basic level a very detailed x-ray.

PETs are good at identifying areas of increased metabolic activity. Many times that will be cancer, but there are also false positives from PET scans, in the case of things like infections and injuries, where metabolism is also increased. PETs are also not so good at picking out very small areas of concern -- there's simply not enough metabolic activity there for them to pick up.

CTs don't identify hypermetabolic activity but they provide very detailed images. In my experience I got PETs early on, but once my cancer was definitely diagnosed I have gotten mostly CT scans, as well as MRIs.

I hope that helps.


Raco - (4/10/2019 - 12:58pm)

Thank you for your reply. I see where alot of people get CT Scans more often than PET.  I got diagnosed with Melanoma on left flank and two lymphnodes with metastatic cancer.  everything removed with clear margins but I was now listed as stage 3. 

I started Opdivo April 5 th 2018 and finished March 21st 2019 (26 total) during that time, I have had 3 Brain MRI and 3 PET Scans. All came back clear. So I guess my Dr will have a plan for future visits scan etc for X amount of years........   THis is going to be so weird not going for treatment everyother Thursday for the last year.  Crazy

ed williams - (4/10/2019 - 1:02pm)

Hi Raco, sound like your medical team is managing your situation nicely!!! Nice job with the difference between scans Bill!!!!

mrsaxde - (4/11/2019 - 11:04am)

Thanks Ed! It's my background as an educator. I'm just programmed to explain things and to tell the truth. Gets me into trouble on Facebook sometimes. LOL


gopher38 - (4/10/2019 - 1:00pm)

I'm not the op, but thanks for the comments.  Very helpful. 

mandyjill - (4/10/2019 - 1:50pm)

The only PET scan I have had was right after cancer was found from my SLNB.  That was almost 2 years ago.  Every since then I have had a CAT scan evey 3 months (as required as part of the clinical trial I was in).

KellyH - (4/10/2019 - 2:01pm)

Hi Raco. 

My son was also Stage 3...positive sentinel node, no other positive nodes. He will be finishing his year of Opdivo treatment the end of May, only 3 more to go!!! I agree it will be very weird to not be going for treatment every other Thursday....bittersweet. We saw the PA with every treatment, it was a little sense of comfort for me knowing someone from his medical team was looking at him every 2 weeks....

On diagnosis my son had a PET scan. And then halfway through his treatments he had CT scans of his brain, his neck, and his chest, all negative.  His primary tumor was on his scalp. We are scheduled for the same scans following treatment. We just discussed a follow up plan at last treatment. Looks like we will be doing CT scans every 4 months for the first year.  I have read people who went every 3 months and I have read people have done every 6 months. My son is only 18 and the doctors are concerned about the radiation exposure every 3 months, so we are thinking about compromising on every 4 months...3 scans instead of  only 2 with the every 6 month plan or 4 with the every 3 month plan for  the first year. 

I think that every doctor has their preference...but I have read a lot of  folks say their follow up is just CT scans. My son prefers the CT scans as well, less preparation but unfortunately you do what you gotta do to keep this monster away!!! 

Good luck to you!!!  Best wishes always!! 

Kelly :) 


A Melanoma mom ❤️

stevek1959x - (4/10/2019 - 2:59pm)

I've had a total of 3 PET/CT scans since my diagnosis.  The first one was right after my biopsy and diagnosis and the next two were after 3 months of Nivo.  They scheduled  a 3rd one because the second one showed some activity where I had a clnd and they wanted to rule out any uptake( cancer).  The 3rd one revealed even less SUV so they kind of suspect this is from the surgery but they said they will continue to watch it.  I've just finished my 24th and final treatment of Nivo (every two weeks) and have another PET/CT scheduled for mid June (fingers crossed as usual).  So I get both a PET and CT in one pass.

Johnjk04 - (4/10/2019 - 3:06pm)

Yale - New Haven (Smilow Cancer Hospital) does't use PET scans. All of the imaginings that I have received in the past eleven years have been CT and brain MRI.

John J Kissane

Raco - (4/16/2019 - 10:34am)

Thank you all for your input. So, my Dr. is only talking PET scans every 4 to 5 months and My nuro dr wants a brain MRI done once a year.

I still wounder why some use PET and others use CT.   does not seem to be a pattern.