Dr. Eric Rohren is the chair of the department of radiology at Baylor College of Medicine.
Prostatepedia spoke with him about imaging metastatic prostate cancer.
Subscribe to read Dr. Rohren’s comments on radium therapy + imaging. Members can read the interview in their March 2018 issue of Prostatepedia.
In terms of imaging, what kinds of scans can determine if a man has metastases (mets) anywhere in his body?
Dr. Eric Rohren: X-ray has been around for a long time and still has a role to play. It’s easy to obtain, it’s cheap, and it has low radiation exposure. We still rely on a good old-fashioned chest or bone X-ray, depending on the patient’s symptoms.
These days, most patients with any type of malignancy, and specifically prostate cancer, are managed in a couple of ways.
One way is a CAT scan. CAT scan is a 3-D imaging technique that uses X-rays that can take images of the body, chest, abdomen, and pelvis. Most patients with newly diagnosed prostate cancer or treated prostate carcinoma have undergone a CAT scan at some point in the course of their disease. CAT scans can show us the prostate gland, lymph nodes, liver, and many of the different organs where cancer may be hidden.
To supplement that, patients with prostate cancer often get a bone scan, which is a nuclear medicine technique. In a bone scan, we inject radioactive material that goes to the skeleton, and most strongly so in areas where there’s increased skeletal turnover, where something in the bone is inciting a reaction. It may go to benign things like healing fractures, arthritis, and various areas of injury. But the radioactive material also goes to areas of metastatic disease in the skeleton, and it localizes most particularly in those areas, lighting up on these bone scans.
Rather than just a particular region of the body, a bone scan shows us from the top of the head all the way down to the feet, which is nice. We get a look at the entire skeleton, and we can look for the little spots that are lighting up that may indicate the presence of metastatic disease in the skeleton.
CAT scans and bone scans are very widely used. A bone scan is a little bit better than a CAT scan in looking for these bone metastases, so the two really augment each other in detection of the disease.
Beyond these, we do have some newer imaging techniques coming into play. There’s a way of doing a bone scan with PET scanner. A PET scanner is another nuclear medicine technique that is more sensitive than a standard nuclear medicine camera, and it acquires a CAT scan at the same time. You can look at the images on the nuclear medicine technique overlaid on the CT scan to see where exactly the activity is and what it’s due to.
We can also use some agents with PET scanning to look at the skeleton. A so-called fluoride PET/CT bone scan seems to have many advantages over a conventional bone scan in terms of detecting smaller disease, more sites of disease, and things like that. MRI is also used in some cases.
Traditionally, MRI is used to evaluate specific areas, so if there’s pain in a particular area such as the skeleton,
MRI is a great way to do that. MRI is also used to look directly at the prostate gland and at the prostate bed after prostate surgery or after other therapy in the pelvis. It can be very good at detecting small volumes of disease. The problem with PET scanning and MRI scanning is that they are less accessible, although MRI is in most places now, and most major areas have access to a PET scanner.
Then there’s the issue of cost. Both techniques are costly. We need to determine if the added cost is justified by the additional information that those scans provide.
Beyond these techniques, the exciting thing for nuclear medicine is the new developments on the horizon. As we discover more about the molecular nature of disease, why cancer forms, and what makes and defines a cancer cell, those molecular discoveries can be translated into imaging studies that we can then use with PET scanning to be even more sensitive for detection of disease.
For example, there are several new molecular tracers in the United States that are approved for imaging of prostate cancer. Choline and Axumin (FACBC) are both agents approved in the United States for use with PET/CT.
Internationally, people are moving to a compound called prostate surface membrane antigen (PSMA) that can image prostate carcinoma. It seems to be even better than Choline or Axumin. The data is still a little bit undetermined at this point, but there’s a lot of excitement around these newer agents being able to seek out cancer in very small volumes anywhere it occurs in the body.
Then I guess the question becomes: when do you treat?
Dr. Rohren: Yes. That is very much the question. As we discover more and more sites of disease and smaller sites of disease, the question becomes: do we need to treat those aggressively or conservatively? We’re discovering new things about tumor biology, and we need to understand how that gets translated into the best appropriate therapy for patients.