What Medical, Urologic, and Radiation Oncologists Want from Molecular Imaging of Prostate Cancer

Tracking Docetaxel-Induced Cellular Proliferation Changes in Prostate Tumor-Bearing Mice with 18F-FMAU PET

OBJECTIVES

The aim of this exploratory preclinical study was to evaluate the efficacy of 18F-FMAU PET in quantitatively measuring cellular proliferation changes in response to a chemotherapeutic agent in experimental prostate cancer models.

METHODS AND MATERIALS

Docetaxel (DTX) ‒ a standard therapy agent in castrate-resistant metastatic prostate cancer was used as the chemotherapy drug. Athymic male nu/nu mice were inoculated with PC-3 cells in the right flank. After the tumor diameter reached 5 mm, DTX (24 mg/kg) was injected intravenously twice a week, whereas the control group was intravenously administered with saline. The tumor size and body weight were monitored, and longitudinal PET scans were acquired with 18F-FMAU to evaluate tumor cellular proliferation. 18F-FMAU PET scans were performed at 2 hours post-injection of 18F-FMAU on days 0, 11, 18, and 22. Biodistribution studies were carried out after the PET scan on day 22.

RESULTS

Consecutive administrations of DTX were effective in inhibiting PC-3 tumor growth compared to the control group. For PET imaging, PC-3 tumor uptake of 18F-FMAU in the DTX group was increased significantly from 3.09 ± 0.60 %ID/g (day 0) to 5.32 ± 0.37 %ID/g (day 22), whereas the 18F-FMAU tumor update in the control group remained relatively stable on day 0 (2.37 ± 0.51 %ID/g) vs. day 22 (1.83 ± 0.22 %ID/g). The tumor-to-muscle uptake ratio of 18F-FMAU was increased from 2.63 ± 0.20 (day 0) to 5.91 ± 1.1 (day 22) in the DTX group. On day 22, no statistical significance was observed in the tumor-to-muscle uptake ratio of 18F-FMAU in the DTX group vs. the control group. The tumor-to-liver uptake ratio of 18F-FMAU was also similar on day 22 in the DTX group (4.29 ± 0.09) vs. the control group (3.83 ± 0.59).

CONCLUSION

18F-FMAU uptake in implanted PC-3 tumors increases with DTX despite inhibiting tumor growth. Further investigation is needed to decipher the underlying biological mechanism of this apparent flare effect and its relation to the predictability of tumor response to DTX.

Imaging Recommendations for Theranostic PET-CT in Oncology

We in this article have presented a review of the guideline recommendations on theranostic positron emission tomography-computed tomography (PET-CT) imaging which will be helpful to assist practitioners in providing appropriate patient care. Multiple guidelines by different societies and medical associations provide standards for diagnosis, imaging, and treatment of cancer patients. They have generated a number of recommendations related to 68Ga-DOTATATE and 68Ga-PSMA-11 PET-CT, which are the classical examples of theranostic PET-CT imaging in current practice.

Theranostics in Nuclear Medicine: Emerging and Re-emerging Integrated Imaging and Therapies in the Era of Precision Oncology

Theranostics refers to the pairing of diagnostic biomarkers with therapeutic agents that share a specific target in diseased cells or tissues. Nuclear medicine, particularly with regard to applications in oncology, is currently one of the greatest components of the theranostic concept in clinical and research scenarios. Theranostics in nuclear medicine, or nuclear theranostics, refers to the use of radioactive compounds to image biologic phenomena by means of expression of specific disease targets such as cell surface receptors or membrane transporters, and then to use specifically designed agents to deliver ionizing radiation to the tissues that express these targets. The nuclear theranostic approach has sparked increasing interest and gained importance in parallel to the growth in molecular imaging and personalized medicine, helping to provide customized management for various diseases; improving patient selection, prediction of response and toxicity, and determination of prognosis; and avoiding futile and costly diagnostic examinations and treatment of many diseases. The authors provide an overview of theranostic approaches in nuclear medicine, starting with a review of the main concepts and unique features of nuclear theranostics and aided by a retrospective discussion of the progress of theranostic agents since early applications, with illustrative cases emphasizing the imaging features. Advanced concepts regarding the role of fluorine 18-fluorodeoxyglucose PET in theranostics, as well as developments in and future directions of theranostics, are discussed. ^©RSNA, 2020 See discussion on this article by Greenspan and Jadvar.

General Concepts in Theranostics

Theranostics describes the pairing of diagnostic biomarkers and therapeutic agents with common specific targets. Nuclear medicine is the greatest theranostics protagonist, relying on radioactive tracers for imaging biologic phenomena and delivering ionizing radiation to the tissues that take up those tracers. The concept has gained importance with the growth of personalized medicine, allowing customized management for diseases, refining patient selection, better predicting responses, reducing toxicity, and estimating prognosis. This work provides an overview of the general concepts of the theranostics approach in nuclear medicine discussing its background, features, and future directions in imaging and therapy.

18F-Fluciclovine PET/CT Detection of Recurrent Prostate Carcinoma in Patients With Serum PSA ≤ 1 ng/mL After Definitive Primary Treatment

PURPOSE

The aims of this study were to report on our initial experience using F-fluciclovine PET/CT to detect recurrent prostate carcinoma in patients with low serum prostate-specific antigen (PSA) after definitive treatment of primary disease and to conduct a preliminary investigation for factors associated with positive scan findings.

PATIENTS AND METHODS

In this retrospective study, F-fluciclovine PET/CT scans from 28 men with suspected recurrence of prostate carcinoma and PSA values of 1 ng/mL or less were examined to identify the site(s) of disease recurrence. Differences in detection rate for Gleason scores of 7 and greater than 7, T2 and T3 disease, negative and positive surgical margins, and negative and positive seminal vesicle invasion were compared using the Fisher exact test. Mean PSA and mean PSA doubling time of patients with positive scans and negative scans were compared using the independent 2-group t test.

RESULTS

At least one site of disease recurrence was identified in 13 (46.4%) of 28 patients. Disease detection rate was significantly higher in patients with history of Gleason score greater than 7 (Fisher exact test, P = 0.004). Mean PSA and PSA doubling time were not significantly different between patients with positive and negative F-fluciclovine PET/CT scans (P = 0.29 and 0.70, respectively).

CONCLUSIONS

Detection of recurrent prostate cancer using F-fluciclovine PET/CT is possible in patients with low but rising PSA levels of 1 ng/mL or less. In such patients, local and nodal recurrences are more common than distant metastasis, and Gleason score greater than 7 is associated with positive scan results.

Clinical perspectives of PSMA PET/MRI for prostate cancer

Prostate cancer imaging has become an important diagnostic modality for tumor evaluation. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) has been extensively studied, and the results are robust and promising. The advent of the PET/magnetic resonance imaging (MRI) has added morphofunctional information from the standard of reference MRI to highly accurate molecular information from PET. Different PSMA ligands have been used for this purpose including 68gallium and 18fluorine-labeled PET probes, which have particular features including spatial resolution, imaging quality and tracer biodistribution. The use of PSMA PET imaging is well established for evaluating biochemical recurrence, even at low prostate-specific antigen (PSA) levels, but has also shown interesting applications for tumor detection, primary staging, assessment of therapeutic responses and treatment planning. This review will outline the potential role of PSMA PET/MRI for the clinical assessment of PCa.

Diagnostic sensitivity of Tc-99m HYNIC PSMA SPECT/CT in prostate carcinoma: A comparative analysis with Ga-68 PSMA PET/CT

BACKGROUND

Emerging data from published studies are demonstrating the superiority of Ga-68 PSMA PET/CT imaging in prostate cancer. However, the low yield of the Ge-68/Ga-68 from which Gallium-68 is obtained and fewer installed PET/CT systems compared to the SPECT imaging systems may limit its availability. We, therefore, evaluated in a head-to-head comparison, the diagnostic sensitivity of Ga-68 PSMA PET/CT and Tc-99m PSMA SPECT/CT in patients with prostate cancer.

METHODS

A total of 14 patients with histologically confirmed prostate cancer were prospectively recruited to undergo Ga-68 PSMA PET/CT and Tc-99m HYNIC PSMA SPECT/CT. The mean age of patients was 67.21 ± 8.15 years and the median PSA level was 45.18 ng/mL (range = 1.51-687 ng/mL). SUVmax of all lesions and the size of lymph nodes with PSMA avidity on Ga-68 PSMA PET/CT were determined. Proportions of these lesions detected on Tc-99m HYNIC PSMA SPECT/CT read independent of PET/CT findings were determined.

RESULTS

A total of 46 lesions were seen on Ga-68 PSMA PET/CT localized to the prostate (n = 10), lymph nodes (n = 24), and bones (n = 12). Of these, Tc-99m HYNIC PSMA SPECT/CT detected 36 lesions: Prostate = 10/10 (100%), lymph nodes = 15/24 (62.5%), and bones = 11/12 (91.7%) with an overall sensitivity of 78.3%. Lesions detected on Tc-99m HYNIC PSMA SPECT/CT were bigger in size (P < 0.001) and had higher SUVmax (P < 0.001) as measured on Ga-68 PSMA PET/CT compared to those lesions that were not detected. All lymph nodes greater than 10 mm in size were detected while only 28% of nodes less than 10 mm were detected by Tc-99m HYNIC PSMA SPECT/CT. In a univariate analysis, Lymph node size (P = 0.033) and the SUVmax of all lesions (P = 0.007) were significant predictors of lesion detection on Tc-99m HYNIC PSMA SPECT/CT.

CONCLUSION

Tc-99m HYNIC PSMA may be a useful in imaging of prostate cancer although with a lower sensitivity for lesion detection compared to Ga-68 PSMA PET/CT. Its use is recommended when Ga-68 PSMA is not readily available, in planning radio-guided surgery or the patient is being considered for radio-ligand therapy with Lu-177 PSMA. It performs poorly in detecting small-sized lesions hence its use is not recommended in patients with small volume disease.