Multiparametric dynamic whole-body PSMA PET/CT using [68Ga]Ga-PSMA-11 and [18F]PSMA-1007

Abstract

Background: Routine prostate-specific membrane antigen (PSMA) positron emission tomography (PET) performed for primary staging or restaging of prostate cancer patients is usually done as a single static image acquisition 60 min after tracer administration. In this study, we employ dynamic whole-body (D-WB) PET imaging to compare the pharmacokinetics of [⁶⁸Ga]Ga-PSMA-11 and [¹⁸F]PSMA-1007 in various tissues and lesions, and to assess whether Patlak parametric images are quantitative and improve lesion detection and image readability.

Methods: Twenty male patients with prostate cancer were examined using a D-WB PSMA PET protocol. Ten patients were scanned with [⁶⁸Ga]Ga-PSMA-11 and ten with [¹⁸F]PSMA-1007. Kinetic analyses were made using time-activity curves (TACs) extracted from organs (liver, spleen, bone, and muscle) and lesions. For each patient, three images were produced: SUV + Patlak parametric images (K_i and DV). All images were reviewed visually to compare lesion detection, image readability was quantified using target-to-background ratios (TBR), and Ki and DV values were compared.

Results: The two PSMA tracers exhibited markedly different pharmacokinetics in organs: reversible for [⁶⁸Ga]Ga-PSMA-11 and irreversible for [¹⁸F]PSMA-1007. For both tracers, lesions kinetics were best described by an irreversible model. All parametric images were of good visual quality using both radiotracers. In general, Ki images were characterized by reduced vascular signal and increased lesion TBR compared with SUV images. No additional malignant lesions were identified on the parametric images.

Conclusion: D-WB PET/CT is feasible for both PSMA tracers allowing for direct reconstruction of parametric Ki images. The use of multiparametric PSMA images increased TBR but did not lead to the detection of more lesions. For quantitative whole-body Ki imaging, [¹⁸F]PSMA-1007 should be preferred over [⁶⁸Ga]Ga-PSMA-11 due to its irreversible kinetics in organs and lesions.

Keywords: Dynamic whole-body PET; Oncology; PSMA; Parametric imaging; Patlak; Prostate cancer.

Fig. 1

Representation of time activity curves for SUV_mean values. In blue are the TACs for [⁶⁸Ga]Ga-PSMA-11, in red the curves for [¹⁸F]PSMA-1007. On the left column, the plots for healthy organs: Above: liver and spleen; middle: parotid gland and lacrimal gland; below: bone and muscle. On the right column: Above: prostate lesions; middle: lymph node lesions; below: skeletal lesions

Fig. 2

Correlation between values from the parametric Ki images as function of the Ki values from full kinetic analyses using the reversible 2CM (left) and irreversible 2CM (right). In blue are the data for [⁶⁸Ga]Ga-PSMA-11, in red [¹⁸F]PSMA-1007. For the analysed organs (A and B), excellent correlation is seen for [¹⁸F]PSMA-1007, whereas for [⁶⁸Ga]Ga-PSMA-11, the correlation was poor, and the multiparametric Ki values were strongly biased. For lymph node and bone lesions (C and D), excellent correlation is seen for both tracers

Fig. 3

Examples of D-WB PET/CT scans performed in patients referred for primary staging of prostate cancer. SUV images are reconstructed using D-WB data from 60 to 70 min, whereas the parametric images of Ki and DV are reconstructed using D-WB data from 40 to 70 min. Above: the example of a D-WB PET/CT scan performed with [⁶⁸Ga]Ga-PSMA-11 displaying only primary disease (arrow). Below: one of the patients scanned with [¹⁸F]PSMA-1007 showing primary disease in the prostate (thick arrow), dissemination to pelvic lymph nodes, as well as multiple small skeletal lesions in the ribs and left humerus (probably unspecific/benign) (thin arrows)

Fig. 4

Distribution of analysed VOIs showing a clear predominance of lesions favouring the tumour-to-background ratio in the parametric images. Main plot with distribution of all VOIs, insert with zoom on area 25 × 25 TBR. The triangle (△) symbol represents prostate lesions, circle (○) symbol represents lymph node lesions, square (□) symbol represents bone lesions

Fig. 5

Distribution of analysed volumes of interest A in healthy organs; B for malignant lesions in the prostate, lymph nodes and skeletal structures. Represented are SUV_mean (on the left) and Ki_mean (on the right) for both tracers. [⁶⁸Ga]Ga-PSMA-11 in represented in blue, [¹⁸F]PSMA-1007 in red

Fig. 6

Correlation of SUV_mean and Ki_mean for lesions. On the left: [⁶⁸Ga]Ga-PSMA-11; on the right: [¹⁸F]PSMA-1007. Inserts containing the lower ranges of SUV_mean and Ki_mean can be seen on both plots