Practice Updates in Prostate Cancer Imaging - Episode 14
A panel of experts review whether bone scans still have a place in prostate cancer imaging.
Neal Shore, MD, FACS: Is there any ongoing role for technetium-99m bone scan, Larry?
Lawrence Saperstein, MD: That’s a good question. We have the intermediate- and high-risk patients who are going to get the PSMA [prostate-specific membrane antigen] PET [positron emission tomography] scans. Where does that leave us? With the low-risk patients getting the bone scan? That doesn’t make sense. I’ll defer of my clinical colleagues; a bone scan historically probably was helpful in defining a baseline. Because it’s very insensitive. We see a lot of things on a bone scan. We see degenerative disease, as Steven said, we see old fractures, we see benign bone lesion. Establishing a baseline might be helpful, but I don’t really see much utility overall.
Steven Finkelstein, MD, DABR, FACRO: What I would say is, when we built towards our status, we were sometimes pushed towards the need to get the tests that we see on the screen today. “I want to order a sodium fluoride PET/CT bone scan. ‘Oh, you can’t do that until you get a tech-99 bone scan.’ OK. I guess I’ll order the tech-99 bone scan.” Now, that wasn’t every patient, that wasn’t every insurer, but there were those cases where you needed to get certain imaging to get to certain tests that we were doing. In 2022, the ability to say we don’t have to get certain tests, you can move directly to a PSMA PET is going to be very liberating for many of us in the ability to get that test and then say, “Oh, this is what it shows.” And if you want to get more detailed image, if you want to get that MRI to look more anatomically, because you have a need to build, say a radiation plan, and you’re worried about a specific aspect of the anatomy, it may make more sense. It’s going to be very liberating again, to be able to offer patients next-generation imaging in this setting.
Neal Shore, MD, FACS: OK. You ordered it, and here are your findings.
Steven Finkelstein, MD, DABR, FACRO: As you can see here there is a lesion in the prostate as was expected. The lesion on the rib is something that we would’ve called a false positive, correct, Lawrence?
Lawrence Saperstein, MD: It’s interesting. Yes. And putting it in perspective, let’s look at it. Going back, if I may, going back to the coronal, this sort of illustrates the coronal, the use of the coronal, that’s an unfused coronal image, not the MIP [maximum intensity projection] this time. It’s a little different. And you see that little spot next to this spleen there, that’s what we’re talking about. Then the fused PET/CT on the bottom. And this also puts it into a nice perspective, because look at the liver and look how this lesion compares to the liver, right? It’s less than the liver. And we were talking about how that’s an important comparison. Then finally, go to the bone scan. That’s a posterior view of a whole-body bone scan. We see that lesion on the rib is quite high, right? There’s some discordance here between what we’re seeing. And we know that that’s insensitive. Then we go up to the final CT image and that is a nonaggressive CT appearing lesion to me. We talk about reticular density on CT. And this is diagnostic of a benign fibrous dysplasia spectrum lesion. And I would feel comfortable with that.
Michael Gorin, MD: I completely agree Dr Saperstein. That was my interpretation of the case as well. And we see this with different benign bony lesions. One that’s classically noted as Paget’s disease. You commonly see low levels of uptake of PSMA radiotracer in those as well. The important thing is that you have an anatomical correlate that basically demonstrates you that it is benign. And so, you know how to better interpret that finding. The real challenge is that when you look at the CT scan and it looks normal, you don’t see anything that convinces you that it’s a benign lesion or metastatic lesion either way and you have PSMA uptake, then the question is, is this prostate cancer or not? We have a paper where we took lesions like that where in the PSMA-RADS [reporting and data system], which we developed, these would be called 3C lesions. Lesions that are in-bone but do not have an anatomic correlate and then we followed those patients and we found that many of them will blossom to have conventional imaging findings consistent with prostate cancer.
Lawrence Saperstein, MD: Just 1 point getting back to that as for the audience, it’s important to understand this is a new modality and as we said there is a learning curve, and we want to be careful about overcalling things. These false positives or these normal variants are important to keep in mind and this is just an example of that.
Michael Gorin, MD: Another classic area where you could see such false positives is in celiac ganglia next to the spinal column because PSMA expression is found in neuronal tissue. PSMA was first discovered as an enzyme that catalyzes what is it N-acetyl-L-aspartyl-L-glutamate in the CNS [central nervous system]. We see low levels of PSMA expression and this ganglia look just like lymph nodes, but you will typically see low levels of expression and you will see them paired on either side of the spine.
Steven Finkelstein, MD, DABR, FACRO: I want to highlight 1 aspect, which is as radiation oncologist, as urologic oncologist, as a nuclear medicine physician, we are all going to look at these pictures for ourselves. We are all going to look at these pictures. It’s when you read the piece of paper and it says there is a mildly radiotracer lesion in the lateral 9th rib and when that happens if you just take that at face value and you don’t do more investigation, that’s when people can get into trouble. This is where the importance of multidisciplinary team, where even if you are medical oncologist and you might not be as used to or comfortable at looking at the pictures yourself, then within your team you have a person who is used to looking at those images and say, “Hey, this might not actually be disease, maybe this guy is an M1. Maybe this guy doesn’t need systemic therapy at this point.”
Michael Gorin, MD: Lantheus has done a very nice job of educating nuclear medicine physicians and radiologist alike about pearls and pitfalls of reading these scans and the SNMMI [Society of Nuclear Medicine and Molecular Imaging] has also taken a real leadership role in providing cases and instruction to their membership to teach them about these sorts of pitfalls that you could see in reading these scans. That effort is going to be well worth it and probably translate to better outcomes for patients.
Lawrence Saperstein, MD: That’s a great point. There are super modules on SNMMI website, so those will be worth looking at.
Transcript edited for clarity.