PET Scan Shows Growing But Focused Tumor

Posted 25 March 2016

Yesterday was a big day for me and radiation. I had a PET/CT scan in the morning, and my first radiation treatment in the afternoon.

I already have the PET/CT results, so this post will focus on those. I’ll describe the radiation experience next.

First, what is a PET scan? It stands for Positron Emission Tomography. Unlike a CT, which generates X-ray radiation and detects physical structures, the PET scan uses positrons coming from a tracer that is injected into the patient, and it detects metabolic activity.

(Just in case you aren’t entirely clear on positrons, a positron is also called an antielectron; it is the antiparticle or the antimatter counterpart of the electron. The PET scanner counts the matched pairs of photons that are emitted when a positron and an electron collide. Is that clear now?)

The PET/CT scanner is a multi-million-dollar device. Sutter doesn’t have its own PET scanner, so there’s one provided by Alliance Imaging that sits outside a Sutter facility part-time. The same trailer covers other hospitals as well.

The machine looks like a CT scanner from the front, but it has a roughly 3-foot-deep tunnel. Behind the donut that is the usual CT mechanism there is the much larger tunnel that is the PET sensor.

The PET scanner is more like a camera than like an X-ray machine; it does not create radiation, but rather detects the positrons emitted by the decaying radioisotope in the FDG that is injected into the patient.

Even more expensive than the PET/CT scanner itself is the cyclotron that is used to create the radioactive tracer isotopes. With a half-life of 110 minutes, the F-18 FDG needs to be created nearby, since there is little time to transport it. The supplier, based in Sacramento, delivers twice a day to Santa Rosa. To account for the travel time and the differing appointment times, they make each dose “hotter” than it will be when it is used.

The images from the PET and CT are combined, since the PET image doesn’t provide any landmarks. The CT shows the structure, and the PET shows where there is high metabolic activity.

Prep and Scan

There’s more prep for a PET scan, compared with a CT scan. They inject a bit of radioactively tagged glucose (FDG), and then they have you rest for 30 minutes.

Then you’re on the machine for about 30 minutes, much longer than a CT. Along the way, they are also capturing CT images, so they can line everything up between the two image sets.

Results

Here’s the radiologist’s write-up of the results, with my explanatory comments inserted.

A total of 16.30 mCi of F-18 FDG was injected intravenously. The blood glucose level was measured at 82 mg/dl. After a 45 minute delay, imaging was performed utilizing a dedicated PET/CT scanner. CT Scanning was done concurrently for attenuation correction and anatomical localization.

Findings

The heterogeneous mass in the region of the transverse duodenum measures approximately 5.4 x 4.6 cm, somewhat increased from prior measurement on the most recent CT as 4.6 x 3.4 cm. This is FDG positive with maximum SUV of 8.7.

MS: This is the bad news. The mass has increased in area by 60%. This is presumably the source of my pain in recent weeks. The SUV (Standardized Uptake Value) of 8.7 shows that the tumor is malignant; the cutoff for benign is 2 to 2.5. The good news is that this is what the radiation is targeting.

There are several closely adjacent smaller masses versus lobulations of the larger mass and on the CT portion of this exam these may have also increased in size including the 2.4 cm lobulation just lateral to the larger mass (maximum SUV 8.3) and a lobulation inferiorly which has a maximum SUV of 13.5.

MS: A “lobulation” is a section divided into lobes. These are the additional parts of the tumor. I’m not clear on whether these lobulations represent additional tumor growth or if they were there before but just not called out in this way.

No abnormal activity is present within the liver.

MS: That is good news! There’s a good-sized spot on my liver in the CTs that they weren’t sure about; it could have been a cyst or a tumor. This result suggests that it is a cyst.

The 0.8 cm nodule at the left lung base is FDG negative.

MS: More good news! There is only one spot that still shows in the CT of my lungs, and it doesn’t light up with the FGD, which suggests (means?) that it is not cancerous.

There is mild dilatation of the left renal pelvis, without any obstructing lesion or stone, and this appears relatively stable. No osseous activity or osseous lesions. Mild degenerative disc disease is present at L5-S1. No pelvic mass to account for patient’s sciatica.

MS: No surprises here. I have had sciatic pain the past month or so, and they wanted to check to be sure there wasn’t any bone disease. There isn’t.

There is mural thickening of the descending and transverse/distal duodenum and proximal jejunum, appearing somewhat more prominent than on the prior exam. This is not FDG positive, however.

MS: I think “not FDG positive” means that this isn’t a major concern.

Biliary stent is noted with pneumobilia, an expected finding. The biliary stent appears to have been exchanged since the prior CT scan.

MS: Pneumobilia means air in the biliary tree, which is expected because of the stent.

Liver cysts are noted.

MS: Yes! Cysts, not tumors.

Conclusion

Patient’s duodenal mass as well as the adjacent smaller masses/lobulations are significantly FDG positive. There appears to have been slight increase in size since the prior CT scan dated 3/3/2016.

MS: As expected, the tumors are malignant. The radiologist calls the size increase “slight”, but it looks pretty substantial to me.

No activity to suggest distant metastases.

MS: Excellent news!