PET scan Questions

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crikklekay
Posts: 142
Joined: Thu Feb 15, 2018 9:47 am
Location: Richmond, VA

PET scan Questions

Postby crikklekay » Fri May 14, 2021 6:50 am

John just left for his first PET scan, we should have the results on Thursday. I’m hoping and praying for a clear scan (man scanxiety is so much worse when his blood work isn’t in normal ranges), but I feel like I need to arm myself with some information just in case. His Onc is horrible about communication outside of office visits so if I have questions I won’t get any decent answers until his next appointment.

I’ve been reading some of the posts on here about PET scans and it sounds like SUV values are how much of the glucose based tracker has pooled in an area? And spots with a high value means there might be something going on? What sorts of questions should I be asking?
Caring for DH John
Stage IIIC, Lymph nodes: 6/22
Chemo: FOLFOX (6)
12/17 ER and emergency surgery
02/18 Hospital w/MSSA infected port, PICC line inserted, chest CT scan showed septic emboli & blood clots
03/18 Hospital w/CDIFF
08/18 CT Scan Clear, NEMD
2018/2019/2021 Colonoscopy Clear
2019/2020/2021/2022 CT Scan Clear
2021 PET scan & MRI show one spot on liver
08/21 Liver surgery to remove spot, confirmed mCRC. Now Stage IV
09/21 Start Folfiri + Avastin
03/22 CEA Rise, continuing chemo

catstaff
Posts: 177
Joined: Wed Mar 03, 2021 11:37 am

Re: PET scan Questions

Postby catstaff » Fri May 14, 2021 7:06 am

It's not exactly pooled, it's how much has been taken up into the cells. Some organs normally light up (e.g. the brain glows brightly since it uses an immense amount of glucose--so PET can't generally see brain mets). So they look for areas that should not be using a lot of glucose. Due to something called the Warburg effect, cancerous cells generally burn glucose more directly than normal cells since they prioritize growth and division over maintenance. So they will pull much more glucose out of the blood than nonmalignant areas.
D/H Dx 10/2019 RC age 61
Clinical T4bN2M1a (common iliac and para-aortic lymph nodes)
MSS KRAS G12D
CRT 11/19-1/20 FOLFOX 3/20-7/20
Pelvic exenteration w/LAR 8/20
ypT4bN0Mx G3 0/14 nodes LVI not seen PNI-
CEA 10/19:20, 1/20-11/20:1.6, 4.3, 3.4, 2.7, 2/21:9.0 3/21:18,40 4/21:28,19, 5/21:13.3,8.6
PET 3/21 recurrence in distal nodes, L5 vertebra, pelvis
FOLFIRI+bev 3/21-

User avatar
Green Tea
Posts: 451
Joined: Mon Oct 24, 2016 10:48 am

Re: PET scan Questions

Postby Green Tea » Fri May 14, 2021 9:52 am

crikklekay wrote:... I’ve been reading some of the posts on here about PET scans and it sounds like SUV values are how much of the glucose based tracker has pooled in an area? And spots with a high value means there might be something going on? What sorts of questions should I be asking?

You might want to ask about the possibility of false positives and false negatives in the scan. Sometimes the scans are not clear due to artifacts in the scanning process. The article below gives an idea of some of the problems that can be due to the scanning procedure itself or to the behavior of the patient during the scan, or due to the failure of the patient to follow the prep instructions properly.

https://tech.snmjournals.org/content/33/3/156

Interpreting PET/CT scans is a difficult process and requires a lot of training and experience on the part of the radiologist who is interpreting the scan. Sometimes what they say in the "Interpretation" part of the report is not really accurate.

A given PET/CT scan can be sent out to a different hospital for a second opinion if the interpretation appears to be ambiguous or uncertain. A second reading of the current PET/CT scan could conceivably come up with a different conclusion. That's what happened in one of my PET/CT scans a few years ago.

catstaff
Posts: 177
Joined: Wed Mar 03, 2021 11:37 am

Re: PET scan Questions

Postby catstaff » Fri May 14, 2021 12:08 pm

To add to Green Tea's warnings, there are also processes other than cancer which can cause excess uptake, particularly inflammation, though high uptake is rarely anything other than malignancy. Radiologists have some guidelines for this. But a lot of reading scans of all types is experience and judgement. There's a fair amount of art involved.
D/H Dx 10/2019 RC age 61
Clinical T4bN2M1a (common iliac and para-aortic lymph nodes)
MSS KRAS G12D
CRT 11/19-1/20 FOLFOX 3/20-7/20
Pelvic exenteration w/LAR 8/20
ypT4bN0Mx G3 0/14 nodes LVI not seen PNI-
CEA 10/19:20, 1/20-11/20:1.6, 4.3, 3.4, 2.7, 2/21:9.0 3/21:18,40 4/21:28,19, 5/21:13.3,8.6
PET 3/21 recurrence in distal nodes, L5 vertebra, pelvis
FOLFIRI+bev 3/21-

crikklekay
Posts: 142
Joined: Thu Feb 15, 2018 9:47 am
Location: Richmond, VA

Re: PET scan Questions

Postby crikklekay » Mon May 17, 2021 8:38 am

Thanks for your replies! Catstaff, you summed that up a lot better than what I have read so far so I appreciate it haha. And it's good to know that inflammation can cause the scan to light up too. Considering the whole reason we're doing this is a rise in CEA, maybe it will show where that inflammation is then?

Green Tea, I had read about the false positives but not the false negatives. No matter the outcome, I'll make sure to ask if anything in the interpretation seems less than absolutely certain and if we need to get a second reading of the scan. That never would have occurred to me, so thank you!

From what I've read, if something shows up then the next step is biopsies or more testing of some kind. Since this test just shows what areas are using a lot of glucose it's not like they will know exactly why it's lighting up right?
Caring for DH John
Stage IIIC, Lymph nodes: 6/22
Chemo: FOLFOX (6)
12/17 ER and emergency surgery
02/18 Hospital w/MSSA infected port, PICC line inserted, chest CT scan showed septic emboli & blood clots
03/18 Hospital w/CDIFF
08/18 CT Scan Clear, NEMD
2018/2019/2021 Colonoscopy Clear
2019/2020/2021/2022 CT Scan Clear
2021 PET scan & MRI show one spot on liver
08/21 Liver surgery to remove spot, confirmed mCRC. Now Stage IV
09/21 Start Folfiri + Avastin
03/22 CEA Rise, continuing chemo

catstaff
Posts: 177
Joined: Wed Mar 03, 2021 11:37 am

Re: PET scan Questions

Postby catstaff » Mon May 17, 2021 10:47 am

*No* imaging can definitively say something is malignant, only a biopsy can do that. It's just that in many cases the probability that what is seen on the scan is cancer is overwhelming.

The type of inflammation that causes a CEA rise may or may not show up on the PET. Also as I said, the level of uptake can be ambiguous. So in many cases a PET will lead to something like a biopsy. In our case, we didn't doubt that what lit up abnormally was cancer, but they wanted a biopsy of the largest (non-bone) met "just to be sure." (The lymph nodes were too small to biopsy.)
D/H Dx 10/2019 RC age 61
Clinical T4bN2M1a (common iliac and para-aortic lymph nodes)
MSS KRAS G12D
CRT 11/19-1/20 FOLFOX 3/20-7/20
Pelvic exenteration w/LAR 8/20
ypT4bN0Mx G3 0/14 nodes LVI not seen PNI-
CEA 10/19:20, 1/20-11/20:1.6, 4.3, 3.4, 2.7, 2/21:9.0 3/21:18,40 4/21:28,19, 5/21:13.3,8.6
PET 3/21 recurrence in distal nodes, L5 vertebra, pelvis
FOLFIRI+bev 3/21-

crikklekay
Posts: 142
Joined: Thu Feb 15, 2018 9:47 am
Location: Richmond, VA

Re: PET scan Questions

Postby crikklekay » Fri May 21, 2021 8:54 am

We got our results back and unfortunately it wasn't the free and clear I was hoping for as a "hypermetabolic lesion" was found on his liver where it is covered by the diaphragm with a SUV value of 15.3. I'm guessing that's why it didn't show on the CTscan? The Onc let us know it is possible it could be something else, though my mind was in a panic so I can't remember the medical term, but with the CEA increase she is concerned it may be cancer. He has an MRI scheduled for next Friday and then we'll get the results the following Tuesday. Based off those results she'll let us know the next step, though it sounds like biopsy is going to be difficult because of the location. She made it sound like if that's the only spot and they aren't 100% sure it isn't cancer she may just have it removed in some fashion since the biopsy would be so hard anyway.

I'm so thankful for this forum, while the possibility the cancer may be back sends me into a panic at least I have a lot of knowledge here from everyone sharing their experiences so I don't feel quite as lost.
Caring for DH John
Stage IIIC, Lymph nodes: 6/22
Chemo: FOLFOX (6)
12/17 ER and emergency surgery
02/18 Hospital w/MSSA infected port, PICC line inserted, chest CT scan showed septic emboli & blood clots
03/18 Hospital w/CDIFF
08/18 CT Scan Clear, NEMD
2018/2019/2021 Colonoscopy Clear
2019/2020/2021/2022 CT Scan Clear
2021 PET scan & MRI show one spot on liver
08/21 Liver surgery to remove spot, confirmed mCRC. Now Stage IV
09/21 Start Folfiri + Avastin
03/22 CEA Rise, continuing chemo

catstaff
Posts: 177
Joined: Wed Mar 03, 2021 11:37 am

Re: PET scan Questions

Postby catstaff » Fri May 21, 2021 5:55 pm

The liver is notoriously difficult to visualize on CT. My DH has simple cysts that appear and disappear on CT. MRI is pretty definitive for the liver, however.
D/H Dx 10/2019 RC age 61
Clinical T4bN2M1a (common iliac and para-aortic lymph nodes)
MSS KRAS G12D
CRT 11/19-1/20 FOLFOX 3/20-7/20
Pelvic exenteration w/LAR 8/20
ypT4bN0Mx G3 0/14 nodes LVI not seen PNI-
CEA 10/19:20, 1/20-11/20:1.6, 4.3, 3.4, 2.7, 2/21:9.0 3/21:18,40 4/21:28,19, 5/21:13.3,8.6
PET 3/21 recurrence in distal nodes, L5 vertebra, pelvis
FOLFIRI+bev 3/21-


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