0:00

Hello and welcome to the PSMA PET Mastery course.

0:04

My name is Dr. Sally Aer and I'm a dual trained radiologist

0:08

and nuclear medicine specialist from Sydney, Australia.

0:11

We are going to start with some basics about PSMA pet,

0:13

talk about why the scans might be indicated

0:15

and how they are conducted

0:16

and then move on to imaging interpretation.

0:19

Okay, let's get started.

0:23

So, prostate cancer is the most common malignancy in men.

0:26

Um, if you discount skin cancers

0:28

and it is the most, the second most common cause

0:30

of cancer related death in men,

0:32

it is diagnosed following detection of a raised PSA

0:34

or prostate specific antigen

0:36

or an abnormal digital rectal examination.

0:39

These examinations are usually prompted when the man

0:42

presents with symptoms

0:44

and these symptoms can include urinary tract symptoms such

0:48

as increased urination overnight

0:49

or noria increased urinary frequency or difficulty emptying

0:54

or completely emptying the bladder.

0:56

Um, although this does have a broad differential including

0:58

benign prostatic hyperplasia, um,

1:01

or they may present with hematuria or blood in the urine.

1:04

And unfortunately in some cases, and we wanna try

1:06

and prevent this, the men can present with symptoms related

1:09

to metastasis such as bone pain in the setting

1:11

of skeletal metastasis to the spine.

1:15

Briefly, we're going to stop here at prostate anatomy

1:18

and we will revisit this later in the course.

1:21

So the prostate, we think about the base being up close

1:24

to the bladder and then the apex being um, more inferiorly.

1:27

So almost like an inverted kind of current or pyramid.

1:31

There are four specific zones,

1:33

but we can combine the central zone

1:35

and transition zone to give the central gland.

1:37

Moving from the base of the gland, we have the central zone,

1:40

which is marked in this kind of dark purple blue

1:43

and that's more posteriorly.

1:44

And at the front is the fibromuscular stroma.

1:46

Now this is important 'cause this doesn't

1:47

contain glandular tissue.

1:49

So invasion of this structure is important when you're

1:51

looking at MRI interpretation, which is well

1:54

outside the scope of this presentation today.

1:56

As we move more inferiorly

1:58

and we've gotten here at axial size two, we are seeing more

2:00

of the transition zone marked in green.

2:02

And then you'll also notice that the urethra starts more

2:04

anteriorly and then moves kind

2:05

of more centrally and posteriorly.

2:07

The more inferiorly you move through the gland relative

2:09

to the remainder of the tissue surrounding it.

2:12

Coming down at three, we've got that transition zone.

2:15

And also at two and three at that posterior

2:18

and lateral aspect of the prostate,

2:20

we have the peripheral zone.

2:23

And this is quite important

2:24

because of the fact that 70%

2:27

of prostate cancers will arise in this peripheral zone

2:30

or the peripheral gland.

2:32

Um, and then coming down towards the apex, you still have

2:34

that peripheral zone as well as more of the transition zone

2:37

and that anterior fibromuscular stroma coming all the way

2:39

down to the apex.

2:42

So 30% of cancers will arise in the central gland,

2:45

which is this blue and green area.

2:47

So we need to be aware that we are looking

2:49

for abnormal increased uptake

2:51

and we are talking about PET in this series,

2:54

abnormal increased uptake in different parts of the gland

2:57

and then considering that in the context

2:58

Of other imaging or the patient's presentation.

3:03

So coming back a section

3:05

and we're just going to think about

3:06

how prostate cancer spreads in the body.

3:09

And I believe that when I'm interpreting my images, one

3:11

of the most important things to do is

3:12

to think about the pathology of the tumor

3:15

and how it spreads through the lymphatics, how it interacts

3:18

with the structures around it.

3:20

And I really use that to hone my search patterns in imaging

3:23

interpretation and lymph nodes are no different.

3:26

So the first place that

3:27

that prostate cancer typically spreads

3:29

to is the pelvic lymph nodes

3:30

and these are the ones contained within the true pelvis.

3:32

And that kind of comes into staging that we'll see later.

3:36

That N one disease is nodes contained within the true pelvis

3:39

below the pelvic brim, but discounting common iliac

3:42

and inguinal lymph nodes, they're considered M1

3:45

or metastasis one or distant nodes.

3:48

Um, but once they have spread to the pelvis, they do tend

3:51

to follow those big vessels.

3:52

So following the iliac vessels

3:54

through the common iliacs into the

3:56

retroperitoneum around the aorta.

3:57

And that's really important when we think about metastasis

4:01

bone far and away, the most common, uh,

4:03

that has been reported, which comes into why traditionally

4:06

prostate cancer was staged with bone scans.

4:08

Um, as we knew that a good proportion

4:10

of metastatic disease did affect the bones

4:13

that said metastasis can go

4:15

to other organs including the lung, the liver,

4:17

pleura, adrenal glands.

4:18

And I have seen some cases that have gone to the brain.

4:22

So thinking about the imaging modalities

4:23

with prostate cancer as well.

4:26

So if we look at diagnostic radiology, we have MRI

4:29

and here's a tumor here at the anterior aspect.

4:32

And then we also have ct, which is really the mainstay

4:35

for imaging of a lot of other tumor modalities.

4:39

And I do a lot of lung cancer as well in addition

4:41

to my general um, PET and PSMA work.

4:44

And I know that for our lung cancer patients diagnostic CT

4:48

so far and away the most um, common investigation

4:51

that we use in radiology, but it's less

4:53

useful in prostate cancer.

4:55

Um, this she case with the blue ring shows

4:57

that the patient does have an enhancing lesion in the

5:00

prostate, but this isn't the norm.

5:01

Often the lesions you cannot see

5:03

and often the lymph nodes that are involved are small

5:06

and with CT we have our size criteria that we use

5:08

for interpretation, but if they are less than a centimeter,

5:13

we may not detect them

5:14

and that's where other modalities really come in handy.

5:17

Um, also with ct it's great for looking at bone lesions, um,

5:20

but if they are not developing a sclerotic

5:23

or a lytic response within the bone, then we may miss them.

5:28

So with as, just to summarize, those limitations of ct um,

5:31

include um, that we have limited assessment

5:34

of the primary tumor in many cases

5:36

and also that there can be a size assessment

5:38

of the node limitation.

5:40

And so we may Ms. Small volume local recurrence,

5:42

which often happens when we have just a small elevation in

5:45

PSA in a previously treated patient.

5:49

In terms of thinking about nuclear medicine,

5:51

we have traditionally relied on technician 99

5:53

and bone scans which use a bisphosphonate

5:55

analog. And so we're looking at

5:56

Osteoblastic activity.

5:57

So the osteoblast takes out the tracer

6:00

for the radiopharmaceutical from the blood

6:01

and deposits it into bone.

6:03

So we have a surrogate measure of bone turnover.

6:06

Um, but this relies on a few things that the fact

6:09

that we need to have bone metastases

6:10

and that those bone metastases are osteoblastic.

6:13

The majority are, but not all are.

6:16

And we don't really get a good sense of the soft tissues,

6:19

particularly the lymph nodes.

6:21

But of course bone scans aren't our only option

6:23

and we now have A-P-S-M-A PET CT

6:25

to help stage these patients

6:28

and that is what this whole mastery course is about today.

6:30

And here's an example. We not only are able

6:33

to image the skeleton in this case,

6:34

which does have quite widespread skeletal metastases,

6:37

but the primary tumor, the soft tissues

6:39

and metastases affecting other organs besides the skeleton.

6:42

So in summary, the limitations of bone scans,

6:45

which have meant that it is less useful compared

6:47

to PSMA PET include that it gives assessment

6:50

of the skeleton only.

6:52

It only also images osteoblast metastases.

6:55

And I do put an asterisk here as we can sometimes see

6:58

NIA in regions of lytic metastases.

7:00

And we do have SPECT cts,

7:02

so the functional plus the low dose CT imaging

7:04

that we confuse together for increasing that interpretation.

7:08

Um, but typically osteoblastic lesions is

7:10

where bone scans shine, which isn't always the case.

7:14

We image, um, patients for bone scans four hours

7:16

after injection of tracer compared to gallium,

7:19

which is we image them an hour after injection.

7:21

So we've got a shorter access, shorter time.

7:24

Um, and then there's also inherent limitations in spatial

7:27

resolution and that we are looking at a scan which is

7:31

sensitive but not necessarily specific.

7:33

And what do I mean by that?

7:34

I mean that a bone scan will pick up any cause

7:36

of increased bone turnover, whether that be infection

7:39

or arthritis or um, even a healing fracture.

7:42

So there's a huge differential

7:44

and sometimes even though it's really useful in detecting

7:47

and very sensitive for osteoblastic metastases,

7:49

there can still be some diagnostic uncertainty with that.

7:54

And just to close off this first section,

7:56

I just thought I would showcase one example of

7:59

how we can use diagnostic radiology with that MRI

8:02

or the multiparametric MRI of the prostate in conjunction

8:06

with our PSMA pets.

8:07

And here is a lesion anteriorly within the gland at the

8:10

base, and corresponding to that focal increased uptake

8:15

of the PSMA ligand tracer,

8:17

which we'll learn about a little bit more in the upcoming

8:19

modules.