Hallmarks in prostate cancer imaging with Ga68-PSMA-11-PET/CT with reference to detection limits and quantitative properties

Assessment of volumetric parameters derived from 68Ga-PSMA PET/CT in prostate cancer patients with biochemical recurrence: an institutional experience

OBJECTIVE

The aim of this study was to evaluate the relationship between volumetric parameters calculated using semiautomatic quantification of lesions detected in 68Ga-labeled prostate-specific membrane antigen PET-computed tomography (68Ga-PSMA PET/CT) and clinical characteristics in prostate cancer (PCa) patients with biochemical recurrence.

METHODS

A total of 85 consecutive PCa patients with biochemical recurrence who underwent 68Ga-PSMA PET/CT at our institution from January 2019 to March 2020 were retrospectively assessed. 68Ga-PSMA PET/CT-derived volumetric parameters, including whole-body PSMA tumor volume (wbPSMA-TV) and whole-body total lesion PSMA (wbTL-PSMA), as well as the established maximum and mean standardized uptake value (SUVmax and SUVmean), were calculated for each patient. All PET-derived parameters were analyzed for correlation with prostate-specific antigen (PSA) levels and for association with Gleason scores.

RESULTS

Eighty-five patients with a mean age of 68.9 ± 7.8 years (range, 47-83 years) and a mean PSA level of 40.9 ± 92.1 ng/ml (range, 0.2-533.2 ng/ml) were analyzed. Volumetric parameters, that is, wbPSMA-TV and wbTL-PSMA, demonstrated a statistically significant correlation with PSA levels (r = 0.403 and r = 0.556, respectively, all at P < 0.001) and only the means of wbTL-PSMA were significantly different between the Gleason score groups (P < 0.05).

CONCLUSIONS

The results of our study indicate that 68Ga-PSMA PET/CT might be a valuable tool for the detection and follow-up of recurrence in PCa patients. 68Ga-PSMA PET/CT-derived quantitative volumetric parameters demonstrated a highly significant correlation with changes in PSA levels. Larger prospective studies are needed to help reveal the full potential of parameters such as PSMA-TV and TL-PSMA derived from PET imaging with 68Ga-PSMA.

Clinically Applicable Cyclotron-Produced Gallium-68 Gives High-Yield Radiolabeling of DOTA-Based Tracers

By using solid targets in medical cyclotrons, it is possible to produce large amounts of ⁶⁸GaCl₃. Purification of Ga³⁺ from metal ion impurities is a critical step, as these metals compete with Ga³⁺ in the complexation with different chelators, which negatively affects the radiolabeling yields. In this work, we significantly lowered the level of iron (Fe) impurities by adding ascorbate in the purification, and the resulting ⁶⁸GaCl₃ could be utilized for high-yield radiolabeling of clinically relevant DOTA-based tracers. ⁶⁸GaCl₃ was cyclotron-produced and purified with ascorbate added in the wash solutions through the UTEVA resins. The ⁶⁸Ga eluate was analyzed for radionuclidic purity (RNP) by gamma spectroscopy, metal content by ICP-MS, and by titrations with the chelators DOTA, NOTA, and HBED. The ⁶⁸GaCl₃ eluate was utilized for GMP-radiolabeling of the DOTA-based tracers DOTATOC and FAPI-46 using an automated synthesis module. DOTA chelator titrations gave an apparent molar activity (AMA) of 491 ± 204 GBq/µmol. GMP-compliant syntheses yielded up to 7 GBq/batch [⁶⁸Ga]Ga-DOTATOC and [⁶⁸Ga]Ga-FAPI-46 (radiochemical yield, RCY ~ 60%, corresponding to ten times higher compared to generator-based productions). Full quality control (QC) of ⁶⁸Ga-labelled tracers showed radiochemically pure and stable products at least four hours from end-of-synthesis.

Comparison of the diagnostic utility of 99mTc-PSMA scintigraphy versus 68Ga-PSMA-11 PET/CT in the detection of metastatic prostate cancer and dosimetry analysis: a gamma-camera-based alternate prostate-specific membrane antigen imaging modality

OBJECTIVE

The present study was performed for head-to-head comparison between 68Ga-prostate-specific membrane antigen (PSMA) PET/computed tomography (CT) and 99mTc-PSMA whole-body and regional single-photon emission computed tomography (SPECT)/CT for the detection of prostate cancer metastases.

METHODS

Ten patients with metastatic prostate cancer underwent 99mTc-PSMA whole-body scan after intravenous injection of 230-330 MBq 99mTc-PSMA. Anterior and posterior whole-body images were acquired at 10 min, 2, 4 and/or 5/6 h post-injection. Additional SPECT/CT images were acquired for the involved sites, where planar images did not clearly identify the metastatic sites. All patients also underwent whole-body 68Ga-PSMA PET/CT and the results between the two techniques were compared for the detection of the metastatic lesions. Dosimetry analysis of the 99mTc-PSMA studies was performed using the MIRD-OLINDA approach.

RESULTS

68Ga-PSMA PET/CT detected lesions in all 10 patients, whereas 99mTc-PSMA imaging detected lesions in 9/10 patients. 68Ga-PSMA PET/CT imaging identified a total of 112 PSMA avid metastatic lesions compared to 57 (51%) lesions on 99mTc-PSMA imaging. Eighteen out of 57 lesions were detected only on delayed 99mTc-PSMA imaging at 4 h and/or 6 h. The regional 99mTc-PSMA SPECT detected 51/83 (61.0%) lesions seen on 68Ga-PSMA PET/CT. The dosimetry results demonstrated that 99mTc-PSMA provided organs' radiation absorbed/effective doses comparable with 99mTc-PSMA imaging.

CONCLUSION

Whole-body 99mTc-PSMA combined with regional SPECT/CT could be a potential alternative to 68Ga-PSMA PET for the detection of the advanced stage metastatic prostate cancer and for response evaluation to PSMA-based targeted therapies.

Intra-individual dynamic comparison of 18F-PSMA-11 and 68Ga-PSMA-11 in LNCaP xenograft bearing mice

Recently, a ¹⁸F-labeled derivative of the widely used ⁶⁸Ga-PSMA-11 was developed for PET imaging of prostate cancer. Although ¹⁸F-PSMA-11 has already been evaluated in a Phase I and Phase II clinical trial, preclinical evaluation of this radiotracer is important for further understanding its dynamic behavior. Saturation binding experiments were conducted by incubation of LNCaP cells with ¹⁸F-PSMA-11 or ⁶⁸Ga-PSMA-11 for 1 h, followed by determination of the specific and aspecific binding. Mice bearing LNCaP or PC-3 xenografts each received ± 3.7 MBq ¹⁸F-PSMA-11 and ⁶⁸Ga-PSMA-11 followed by dynamic acquisition of 2.5 h as well as ± 15 MBq ¹⁸F-FDG followed by static acquisition at 1 h post injection (p.i.). Uptake was evaluated by comparison of uptake parameters (SUV_mean, SUV_max, TBR_mean and TBR_max). Mice underwent ex vivo biodistribution where ¹⁸F-PSMA-11 activity was measures in excretory organs (kidneys, bladder and liver) as well as bone fragments (femur, humerus, sternum and skull) to evaluate bone uptake. The dissociation constant (K_d) of ¹⁸F-PSMA-11 and ⁶⁸Ga-PSMA-11 was 2.95 ± 0.87 nM and 0.49 ± 0.20 nM, respectively. Uptake parameters were significantly higher in LNCaP compared to PC-3 xenografts for both ¹⁸F-PSMA-11 and ⁶⁸Ga-PSMA-11, while no difference was found for ¹⁸F-FDG uptake (except for SUV_max). Tumor uptake of ¹⁸F-PSMA-11 showed a similar trend over time as ⁶⁸Ga-PSMA-11, although all uptake parameter curves of the latter were considerably lower. When comparing early (60 min p.i.) to delayed (150 min p.i.) imaging for both radiotracers individually, TBR_mean and TBR_max were significantly higher at the later timepoint, as well as the SUV_max of ⁶⁸Ga-PSMA-11. The highest %ID/g was determined in the kidneys (94.0 ± 13.6%ID/g 1 h p.i.) and the bladder (6.48 ± 2.18%ID/g 1 h p.i.). No significant increase in bone uptake was seen between 1 and 2 h p.i. Both radiotracers showed high affinity for the PSMA receptor. Over time, all uptake parameters were higher for ¹⁸F-PSMA-11 compared to ⁶⁸Ga-PSMA-11. Delayed imaging with the latter may improve tumor visualization, while no additional benefits could be found for late ¹⁸F-PSMA-11 imaging. Ex vivo biodistribution demonstrated fast renal clearance of ¹⁸F-PSMA-11 as well as no significant increase in bone uptake.

Detection limit of 89Zr-labeled T cells for cellular tracking: an in vitro imaging approach using clinical PET/CT and PET/MRI

PURPOSE

Tracking cells in vivo using imaging can provide non-invasive information to understand the pharmacology, efficacy, and safety of novel cell therapies. Zirconium-89 (t1/2 = 78.4 h) has recently been used to synthesize [89Zr]Zr(oxinate)4 for cell tracking using positron emission tomography (PET). This work presents an in vitro approach to estimate the detection limit for in vivo PET imaging of Jurkat T cells directly labeled with [89Zr]Zr(oxinate)4 utilizing clinical PET/CT and PET/MRI.

METHODS

Jurkat T cells were labeled with varying concentrations of [89Zr]Zr(oxinate)4 to generate different cell-specific activities (0.43-31.91 kBq/106 cells). Different concentrations of labeled cell suspensions (104, 105, and 106 cells) were seeded on 6-well plates and into a 3 × 3 cubic-well plate with 1 cm3 cubic wells as a gel matrix. Plates were imaged on clinical PET/CT and PET/MRI scanners for 30 min. The total activity in each well was determined by drawing volumes of interest over each well on PET images. The total cell-associated activity was measured using a well counter and correlated with imaging data. Simulations for non-specific signal were performed to model the effect of non-specific radioactivity on detection.

RESULTS

Using this in vitro model, the lowest cell number that could be visualized on 6-well plate images was 6.8 × 104, when the specific activity was 27.8 kBq/106 cells. For the 3 × 3 cubic-well, a plate of 3.3 × 104 cells could be detected on images with a specific activity of 15.4 kBq/106 cells.

CONCLUSION

The results show the feasibility of detecting [89Zr]Zr(oxinate)4-labeled Jurkat T cells on clinical PET systems. The results provide a best-case scenario, as in vivo detection using PET/CT or PET/MRI will be affected by cell number, specific activity per cell, the density of cells within the target volume, and non-specific signal. This work has important implications for cell labeling studies in patients, particularly when using radiosensitive cells (e.g., T cells), which require detection of low cell numbers while minimizing radiation dose per cell.

The Continuing Evolution of Molecular Functional Imaging in Clinical Oncology: The Road to Precision Medicine and Radiogenomics (Part I)

The present era of precision medicine sees 'cancer' as a consequence of molecular derangements occurring at the commencement of the disease process, with morphologic changes happening much later in the process of tumorigenesis. Conventional imaging techniques, such as computed tomography (CT), ultrasound, and magnetic resonance imaging (MRI), play an integral role in the detection of disease at a macroscopic level. However, molecular functional imaging (MFI) techniques entail the visualisation and quantification of biochemical and physiological processes occurring during tumorigenesis, and thus has the potential to play a key role in heralding the transition from the concept of 'one size fits all' to 'precision medicine'. Integration of MFI with other fields of tumour biology such as genomics has spawned a novel concept called 'radiogenomics', which could serve as an indispensable tool in translational cancer research. With recent advances in medical image processing, such as texture analysis, deep learning, and artificial intelligence (AI), the future seems promising; however, their clinical utility remains unproven at present. Despite the emergence of novel imaging biomarkers, a majority of these require validation before clinical translation is possible. In this two-part review, we discuss the systematic collaboration across structural, anatomical, and molecular imaging techniques that constitute MFI. Part I reviews positron emission tomography, radiogenomics, AI, and optical imaging, while part II reviews MRI, CT and ultrasound, their current status, and recent advances in the field of precision oncology.

Radium-223 for the treatment of bone metastases in castration-resistant prostate cancer: when and why

Radium-223 dichloride (²²³Ra) is the first, recently approved, α-particle-emitting radiopharmaceutical for the treatment of patients with bone metastases in castration-resistant prostate cancer (CRPC) and no evidence of visceral metastases. We explored MEDLINE, relevant congresses, and websites for data on ²²³Ra and prostate cancer therapies, focusing on therapeutic strategies and timing, bone metastases, and diagnostic assessment. ²²³Ra represents the only bone-targeting agent that has significantly extended patients' overall survival while reducing pain and symptomatic skeletal events. Unlike other radiopharmaceuticals, such as strontium-89 and samarium-153 EDTMP, ²²³Ra (11.4-days half-life) has shown a high biological efficiency mainly due to its short penetration range. These features potentially allow reduced bone marrow toxicity and limit undue exposure. ²²³Ra has been validated under the product name Xofigo^® by the US Food and Drug Administration and the European Medicines Agency. Patient selection, management, and treatment sequencing is recommended to be discussed in the context of a multidisciplinary environment, including oncology, urology, nuclear medicine, and radiation therapy physicians. No consensus has been achieved regarding the optimal timing and its administration as single agent or in combination with zoledronic acid or chemotherapy, so far. This review aims to provide a rationale for the use of ²²³Ra in treating metastases from CRPC, highlighting the crucial role of a multidisciplinary approach, the disputed inclusion and exclusion criteria on the basis of agencies regulations, and the value of diagnostics for therapy assessment.

Lung Scintigraphy in the Assessment of Aerosol Deposition and Clearance

Environmental and occupational exposure to particulate aerosols is known to have negative health effects. However little is known about how these aerosols trigger the development of pathophysiological mechanisms in the body or the fate of ultrafine particles in the lungs after inhalation. The development of aerosols of different origin that can be labeled to a large variety with radionuclides compatible with clinical gamma camera systems opens the possibility of using lung scintigraphy imaging to study these causalities in detail. Lung scintigraphy (planar or SPECT) allows regional mapping of the deposition of the aerosol in the lungs and the dynamic assessment of particle clearance and translocation from the healthy and affected human lungs. In this paper, we will review the unique features of lung scintigraphy applied to aerosol clearance studies in humans.