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| Fig. 1: Modern Day PET Scanner. (Source: Wikimedia Commons) |
Positron Emission Tomography (PET) scanning (see Fig. 1) was first developed at Washington University in the 1970s. Since then, PET scans have been widely used as diagnostic tools for cardiology and neurology. Only recently have PET scans become used in the field of oncology. [1] Unlike MRI (magnetic resonance imaging) scans, x-rays, or CT (computerized tomography) scans that provide a single snapshot of an area of the body, PET scans can detect biological function. This is why PET scans are more effective as an oncologic diagnostic tool compared to the other methods of imaging. To study the biological function of malignant cells, patients are injected with a positron-emitting radionucleotide attached to a glucose analog. [1] Because cancer cells require much more energy than normal cells in order to divide uncontrollably, malignant cells are characterized by high levels of metabolism; therefore, the changing distributions of the labeled glucose analogs can identify areas of abnormally high levels of metabolism. [1.2] When the radionucleotide decays, it releases a positron which then undergoes an annihilation reaction with an electron, yielding two 511-keV photons. When patients receive a PET scan, they are placed through a collection of 18-24 rings of specific detector crystals that detect the release of these photons. [1,3] One of the drawbacks of using PET scans was its low resolution; however, a PET/CT scan hybrid was created to ensure high resolution imaging of biological processes.
Prostate cancer (shown in Fig. 2) is the third leading cause of oncologic death and is often found in industrialized nations, such as the United States. The age-standardized mortality rate of prostate cancer in the United States is 15.8 per 100,000 people. [4] One of the causes of high mortality rates is due to the inadequacies of current diagnostic techniques in determining the level of metastasis and invasion of the cancer.
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| Fig. 2: PET/CT Scan Images of Prostate Cancer (Source: Wikimedia Commons) |
In the early 2000s, PET scans emerged as effective diagnostic tools for detecting lung, lymphoma, and melanoma cancer; however, PET scans were not used for detecting prostate cancer until nearly two decades later with the development of PET/CT hybrid scans. [2] Loyola University Chicago Stritch School of Medicine Hospital was one of the first hospitals in the Midwest to use this tool for detecting recurring tumors in patients who received treatment for their prostate cancer. The PET/CT scan they use requires the administration of Fluciclovine F-18, a radioactive tracer, which is taken up by malignant prostate cells. The scan then detects the photons released from the decay of Fluciclovine F-18. [5]
Novel research on PET scans and prostate cancer includes the use of Carbon-11-Choline, a radioactive tracer, as a potential replacement for the commonly used radioactive tracer, 18F-fluorodeoxyglucose, which is a radioactive tracer similar to but chemically different from Flucicovine F-18. In clinical trials, 370 MBq of Carbon-11-Choline was intravenously administered to 10 patients, and PET scans were taken 5-10 minutes after the injection. The same patients were also administered 18F-fluorodeoxyglucose on a separate day. When 18F-fluorodeoxyglucose was used, the levels of metastasis and invasion of the malignant cells in the prostate was difficult to determine due to the high amounts of radioactivity in the urine that masked the results; however, when Carbon-11-Choline was used, radioactivity in the urine was nearly negligible, allowing for an accurate image of malignant cell activity in the prostate. [6]
One future application would be the expansion of PET/CT scans to detect levels of metastasis and invasion of malignant tissues in organs other than the prostate (e.g. kidneys, ovaries, etc.) by developing tissue-specific radioactive tracers. Another application of PET/CT scans would be creating affordable, portable machines that can be used during surgery, radiation therapy, or chemotherapy to accurately map out the excision or eradication of malignant tissue. With the advent of technological innovation and research in nuclear medicine, PET/CT scans will play a crucial role in tackling prostate cancer.
© Michelle Bach. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] L. K. Griffeth, "Use of PET/CT Scanning in Cancer Patients: Technical and Practical Considerations," BMUC Proc. 18, 321 (2005).
[2] R. Bar-Shalom, A. Y. Valdiva, and M. D. Blaufox, "PET Imaging in Oncology," Semin. Nucl. Med. 30, 150 (2000).
[3] C. L. Melcher, "Scintillation Crystals for PET," J. Nucl. Med. 41, 1051 (2000).
[4] G.P. Haas et al., "The Worldwide Epidemiology of Prostate Cancer: Perspectives from Autopsy Studies," Can. J. Urol. 15, 3866 (2008).
[5] O.A. Odewole et al., "Recurrent Prostate Cancer Detection with Anti-3-[18F]FACBC PET/CT: Comparison with CT," Eur. J. Nucl. Med. Mol. Imaging 43, 1773 (2016)
[6] T. Hara, N. Kosaka, and H. Kishi, "PET Imaging of Prostate Cancer Using Carbon-11-Choline," J. Nucl. Med. 39, 990 (1998).
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