0:01

In this video, we are going to briefly discuss the role

0:04

of FDG PET CT in brain tumors.

0:07

There are several clinical applications

0:11

for performing an FDG PET ct.

0:13

However, PET is not the main modality

0:17

to evaluate these tumors.

0:19

There is still a role

0:22

and sometimes in differentiating primary brain tumors into a

0:26

low grade versus high grade.

0:29

We could help guide stereotactic biopsies.

0:33

The degree of FDG uptake has been correlated

0:37

with prognostic value, as well as, um,

0:42

there is a role in following lesions

0:46

after therapy to evaluate for viable tumor.

0:51

So in this image, I'm showing you the normal distribution

0:53

of FDG in the brain.

0:55

As we have discussed previously,

0:59

FDG is a glucose analog

1:01

and it will be trapped in the cells

1:04

that are metabolically active.

1:06

And in the brain there is physiologically intense trace

1:10

or uptake, particularly at the great matter.

1:14

So along the, the cortex in the, both in the brain

1:19

and also cerebellum as well as in subcortical grade matter,

1:24

which is in the basal ganglia.

1:26

So as you can imagine, this presents a limitation

1:31

or the evaluation of other lesions

1:34

because there's intrinsically intense background.

1:39

This intense background is

1:41

because neurons, uh, normally use glucose almost exclusively

1:46

to meet its metabolic energy requirements.

1:49

It has been reported in the literature that the ratio of

1:54

great matter uptake

1:55

to white matter uptake is 2.5 to one.

2:00

So that would give you an idea, uh, when you're evaluating

2:04

patients with brain lesions, the same way

2:07

that other malignant tumors elsewhere in the body

2:11

could show different degrees of epi g optic.

2:15

That is also true for brain lesions.

2:19

And the key would be to try to differentiate first

2:24

the presence of a lesion

2:25

and second, try to characterize this lesion better.

2:30

A precise atomic localization

2:32

for these intracranial lesions is very important.

2:36

So having access to the CT on the pet, on the PET C

2:41

or being able to coregister

2:44

with a separate MRI is crucial in these cases.

2:49

And there are softwares that allow you to do correlation

2:53

and co-registration with, uh, separate studies.

2:58

The role of pettine in primary brain tumors

3:02

has been studied, but it's not widely used.

3:06

I'm showing you here a graphic from a nice article published

3:10

in which they studied the differences of

3:14

uptick in three scenarios.

3:17

Uh, metastasis, glioblastoma, multiforme and lymphoma.

3:22

And they compare the uptake of the cortex,

3:27

so tumor to background ratios in the lesion

3:31

and the white matter to try to separate the lesions.

3:36

As you can see, there is in significantly higher tumor

3:39

to background activity ratios

3:41

for lymphoma compared to others.

3:44

There isn't a specific SUV max cutoff,

3:48

but, um, many articles suggest that around

3:53

SUV max 15 one could suggest that the lesion

3:58

could be lymphoma.

4:00

As I said, there's no validation for this,

4:03

and PET CT in these cases is only a modality

4:07

that could help MRI try to narrow down the diagnosis.

4:13

This is an image from the same article

4:16

that shows on the top is the pet,

4:19

and on the bottom we have the fused images

4:22

and the SUV max value values of each.

4:26

The first one corresponds with lymphoma

4:28

with an SUV max of 18.

4:31

The second example, it's a rim like lesion

4:34

with peripheral FDG uptake

4:36

and correspondent to glioblastoma multiforme.

4:40

And the third case is, uh, metastasis.

4:44

So people have used this UV max values as well

4:47

as tumor two background activity ratios

4:51

regarding tumor viability after therapy.

4:54

People have investigated the role

4:58

of dual phase FDG in this article

5:02

that I have listed here,

5:04

and you will have in your references.

5:06

They studied an FDG pit done at 30 minutes

5:11

as a first time point,

5:13

and at three hours as a second time point.

5:16

And they say that

5:19

performing pets in these two time points was helpful

5:23

in evaluated lesions.

5:25

They also explain in the, in their methodology

5:29

how they did the ratios

5:31

of the calculating SUV max within the lesion

5:35

and then the contralateral white matter.

5:38

They also use contralateral coded head

5:41

and ipsilateral cvor cortex.

5:44

And they found ultimately that these values

5:47

that I'm listed here are helpful

5:51

and those would be the recommended values in assessment

5:55

of viability

5:56

After treatment.

5:58

These studies lack validation, so ultimately

6:03

for tumor viability, serial of MRIs as well

6:07

as FDG would probably be done in these patients.

6:13

These is one of the cases

6:16

that was listed in this article,

6:19

and this patient had metastatic breast cancer

6:23

that had been treated

6:25

and patient received whole brain radiation

6:28

and stereotactic radiosurgery

6:29

to treat a lesion in the corpus call.

6:32

And then on the three month follow up,

6:34

the lesion was smaller,

6:37

but later showed that the lesion was enlarging.

6:42

And because it was the treatment side, the question was

6:45

was this radiation necrosis

6:47

or is this recurrence or viable tumor?

6:50

So they perform an earthly pit ct,

6:54

which is shown in the middle, and then a delayed image.

6:58

And as you can see, it's pointing an area

7:00

of progressive increase of tracer uptake.

7:04

The tumor to background ratios suggested that these

7:09

correspondent to viable tumor and

7:12

therefore patient underwent, uh, subsequent therapy.