Are Bone Scans Obsolete? Evolving Imaging Techniques in Prostate Cancer

In the second segment of this roundtable, the panelists discuss the evolving role of imaging techniques in managing prostate cancer. They debate the use of bone scans versus the newer PSMA PET scans, which have revolutionized prostate cancer detection and treatment strategies. The panel explores when to use each imaging method and how PSMA PET scans have changed their clinical practice, particularly in cases of metastatic hormone-sensitive and castration-resistant prostate cancer. They also touch on the challenges of interpreting scan results, especially in differentiating high-volume versus low-volume metastatic disease, and the limitations of older imaging methods.

Watch the third segment of this roundtable: Prognostic Factors in Prostate Cancer: Gleason Scores, PSA Levels, and Genomic Testing

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Dr. Mehta:
Doctor Chablani, one question I have in community is do we think bone scans are obsolete? Do we need to use bone scan as a treatment even just on somebody who is a metastatic, you know, hormone sensitive or castrate resistant prostate cancer? Do you use that for periodic imaging response on a CT or a bone or you usually just do CT scan and only use bone scan as needed?

Dr. Chablani:
I mean, that’s a great question. As we’ve been talking about, PSMA PET has completely revolutionized the field in every stage of prostate cancer from localized to metastatic castrate sensitive to metastatic castrate resistant. I do think there’s this gray area that Doctor Kelly and Doctor Wong have alluded to where a patient is presenting with a PSMA PET scan and there’s disease in a lot of different bones.

So I think when there are these mets everywhere, but they’re low SUVs and I’m worried about false positives, Then I do go ahead and order a regular CTM and CT chest, pelvis, and a nuclear medicine bone scan because from our trials, that’s where we have the data for how to treat low volume versus high volume disease.

On the other hand, if patients present to me with a PSMA PET scan that’s showing clear liver mets or lung mets and visceral disease, then I’m not going to bother to put them through additional testing. And at that point, I’m thinking, you know, probably like triplets versus doublets versus not on the backbone of ADT plus RSI because you know, a lot of these patients are also coming to us. They’ve been seeing many different providers and it’s like 3 months in and they’re like, “I just want to start on a treatment now. Do I have to get more imaging?” So really it’s the nuanced cases where I’m like, is this high volume or is this low volume? Should I be radiating the prostate as well? Or should I not or where I’m ordering the like the CTHS at my polypsis and the bone scan.

And then after patients have had their initial treatment after three to six months and their PSA has gone down and it’s nice and low, that’s when I feel comfortable. Let’s just get the restaging CT test, abdomen, pelvis and bone scan. Let’s get a new baseline. Insurance isn’t going to argue with me. And then we have this new baseline that we can continue to follow. As long as their PSA is staying nice and low like every 6 months or 6 to 12 months, I’ll just keep ordering that CT test, abdomen, pelvis and bone scan.

But then if the PSA starts to rise again and I’m worried about castration resistant disease, I go ahead and order the PSMA PET because as Doctor Wang was talking about, now we have a chance for SBRT or metastasis directed therapy. And if this PSA rises just being driven by one or two spots, then we can maybe keep the patient on the ADT plus ARSA backbone and radiate one or two spots.

So I think yes, PSMA PET has revolutionized the field, but we still need to be using CT and bone scans in some scenarios because that’s what our trials that tell us how to treat patients have done in the past. But in the future, I think bone scans will probably become obsolete years like a few years from now.

Dr. Appleman:
I think the thing I really hate with bone scans is trying to use them to assess response and looking at serial ones because you have flare. If you look at the prostate cancer working group criteria, you wither have a complete response or you have this progression and there’s flare. And PSMA PET, even we know from the Australian study with cabazitaxel versus lutetium PSMA, that it proved that the PSMA PETs are very good for predicting survival with the cabazitaxel group. So even for a non-mechanism based therapy and just eyeballing those scans, maybe I’m wrong, but I just, I feel much more comfortable. I know what’s going on looking at them and once I get a PSMA PET then I can compare apples to apples by ordering them. And thankfully insurance hasn’t caught on to me yet, but maybe they will soon. So I think that it covers the imaging issue again kind of in the background as we hear the data from these trials.

Dr. Mehta:
Are these trials now using PSMA PET as a future marker for response, or they are still struggling to decide what is the right end point for the trial?

Dr. Appleman:
I think they’re still wrestling. I know that there are trials ongoing now where radiographic PFS by CTM bone scan is one of the primary endpoints. I know there are trials that are including PSMA PET, including I believe some registration trials, but has it become part of an accepted endpoint for let’s say a surrogate for survival? Even I would say in my understanding it’s not yet by the FDA and we don’t really have the data yet to value that.