By Eric M. Rohren
The field of medicine is undergoing phenomenal changes in parallel with exciting developments in the fields of genetics, chemistry, and computer science.
Increasingly, the formulaic patterns that guided medical decision-making in the past are being adjusted and refined by empirical data derived from human biology and pathophysiology, not only at a population level, but at a very personal level. In fact, the term “personalized care” is taking on new meaning with the advent of technologies capable of interrogating the fundamental biological machinery of disease within an individual patient, and in a short enough span of time to allow for specific and targeted actions to be taken based on that knowledge.
In the field of imaging, this is illustrated by the remarkable advances being made in molecularly-targeted diagnostics and therapeutics. For many years, imaging physicians have had the ability to employ medical imaging in the care of the patient, including X-rays, CT scans and MR scans. Most imaging techniques give information about structure, such as whether a patient’s bone is fractured. However, there exists a specific subset of imaging, Nuclear Medicine, which is based on function rather than structure. In this field, various compounds are attached to small amounts of radioactive materials. When these radioactive compounds, termed radiotracers, are injected into the body, they target various tissues or organs based on the biological behavior of the particular compound used. By using a sensitive camera, such as Positron Emission Tomography (PET), images are then obtained that show the distribution of the radiotracer. These images are often supplemented with additional imaging, such as a CT scan, to precisely show the location of the radiotracer inside the body.
The ability to target specific tissues in the body with nuclear medicine has opened up new possibilities in many medical fields, particularly in the field of Oncology. With regard to men’s health, new agents are being developed for the detection of prostate cancer. One of the latest to be approved for medical use is 18F-fluciclovine, marketed under the name Axumin. When injected into the bloodstream, this radiotracer localizes to many tissues in the body, but is targeted particularly strongly to prostate cancer cells. A PET/CT scan performed with 18F-fluciclovine can detect very small deposits of prostate cancer cells, allowing for the design of the best therapy for a patient, such as surgery, radiation therapy, or chemotherapy. Such an approach can be very helpful in the scenario of rising serum PSA (an indicator of recurrent cancer), identifying sites of disease which may be undetected by other imaging tests.
Other imaging compounds are being developed for prostate cancer, such as radiotracers targeting prostate serum membrane antigen (PSMA), a molecule present in high quantities on the surface of many prostate cancer cells. Early studies suggest that PSMA-targeting compounds may also be very accurate for the detection of prostate cancer. Furthermore, investigations are underway to determine whether some of these compounds could be modified to become very effective therapies. By connecting the compound to a therapeutic radioisotope rather than a diagnostic one, the targeting of the compound to cancer cells could result in the delivery of localized radiation therapy inside the body, directed specifically at the tumor.
Many further clinical trials are needed to explore the full potential of these combined therapeutic/diagnostic (so-called “theranostic”) radioactive compounds. In the meantime, the use of approved imaging compounds such as Axumin continues to expand. One of the primary barriers to the use of these agents is reimbursement. Although the Food and Drug Administration has determined that Axumin is safe, and is an effective imaging agent for the detection of prostate carcinoma, many insurance companies and third-party payers do not cover its use, considering it and others in its class to be investigational rather than part of standard medical practice. This is not unusual for any new class of diagnostic or therapeutic compound, and it is the responsibility of the medical community to demonstrate through clinical trials and peer-reviewed publication that medical management and patient outcomes are improved with the incorporation of these new agents. In the meantime, however, patients often are given a choice of paying the cost of the procedure themselves or not having the test at all and relying on conventional diagnostic procedures.
Locally, we have found that molecular imaging techniques have enhanced our ability to treat patients with a higher degree of confidence and precision at Baylor College of Medicine. Whereas previously the approaches to patients with suspected recurrent prostate cancer were often based on assumptions and probabilities, we are now able to treat our patients with targeted and customized therapies designed specifically to treat their cancer. Combining the imaging power of PET radiotracers such as Axumin with other advanced imaging methods, such as high-strength parametric MR and image-guided minimally-invasive biopsy techniques, the team at Baylor College of Medicine is at the forefront of the fight against prostate cancer.
In the near future, we hope to take these practices beyond the Texas Medical Center and deliver cutting-edge care to patients closer to home. To achieve this vision, Baylor College of Medicine and Radiology Partners are working together to bring the most advanced diagnostic and therapeutic medical technologies out of the academic center and into our large network of community hospitals throughout the U.S. A prostate cancer imaging program, led by Axumin PET scanning, is an example of the type of game-changing innovation that can arise out of an academic-private partnership such as that between Baylor College of Medicine and Radiology Partners.
About the author: Dr. Eric M. Rohren is professor and chair of Radiology at Baylor College of Medicine in Houston, TX. His clinical and research expertise is in molecular and functional imaging, with nearly two decades of experience in the performance and interpretation of PET/CT studies and general nuclear medicine procedures, including oncologic, neurologic, and cardiac applications. He has published more than 100 articles in peer-reviewed journals, and lectures nationally and internationally on PET/CT. He has previously been a director on the American Board of Nuclear Medicine, including serving as chair of the board. He has led and participated in numerous research studies on diagnostic and therapeutic uses of radiopharmaceuticals, with research interests in targeted radionuclide therapy, volumetric parameters in PET/CT, and combined-modality imaging with PET and MR.