68Ga-PSMA11 PET/CT for biochemically recurrent prostate cancer: Influence of dual-time and PMT- vs SiPM-based detectors

Abstract

Objectives: ⁶⁸Ga-PSMA11 PET/CT is excellent for evaluating biochemically recurrent prostate cancer (BCR PC). Here, we compared the positivity rates of dual-time point imaging using a PET/CT scanner (DMI) with silicon photomultiplier (SiPM) detectors and a PET/CT scanner (D690) with photomultiplier tubes (PMT), in patients with BCR PC.

Methods: Fifty-eight patients were prospectively recruited and randomized to receive scans on DMI followed by D690 or vice-versa. Images from DMI were reconstructed using the block sequential regularized expectation maximization (BSREM) algorithm and images from D690 were reconstructed using ordered subset expectation maximization (OSEM), according to the vendor's recommendations. Two readers independently reviewed all images in randomized order, recorded the number and location of lesions, as well as standardized uptake value (SUV) measurements.

Results: Twenty-eight patients (group A) had DMI as first scanner followed by D690, while 30 patients (group B) underwent scans in reversed order. Mean PSA was 30±112.9 (range 0.3-600.66) ng/mL for group A and 41.5 ± 213.2 (range 0.21-1170) ng/mL for group B (P = 0.796). The positivity rate in group A was 78.6% (22/28 patients) vs. 73.3% (22/30 patients) in group B. Although the performance of the two scanners was equivalent on a per-patient basis, DMI identified 5 additional sites of suspected recurrent disease when used as first scanner. The second scan time point did not reveal additional abnormal uptake.

Conclusions: The delayed time point in ⁶⁸Ga-PSMA11 PET/CT did not show a higher positivity rate. SiPM-based PET/CT identified additional lesions. Further studies with larger cohorts are needed to confirm these results.

Keywords: (68)Ga-PSMA11; PET/CT; PMT; Prostate cancer; SiPM.

Fig. 1

68-year-old patient with BCR PC (PSA 6.2 ng/mL) after initial radiation therapy. ⁶⁸Ga-PSMA11 DMI images (A, maximum intensity projection - MIP; B1-B4, axial PET and fused PET/CT images) show focal uptake bilateral in the prostate bed and a sub-centimeter left internal iliac lymph node (arrows), which are not seen on images from D690 scanner (C1–4, axial PET and fused PET/CT images; D, MIP). Prostate biopsy revealed prostate adenocarcinoma in the medial base, medial apex and lateral mid, only on the right side and benign tissue in the left prostate, with radiation effect. Subsequently, androgen deprivation therapy and proton beam therapy to the right pelvic and right iliac nodes as the disease burden was located on the right side. Therefore, we have no correlation for whether the left internal iliac lymph node might be false positive. PSA decreased to undetectable level within 6 months after ⁶⁸Ga-PSMA11 imaging.

Fig. 2

87-year-old patient with BCR PC (PSA 0.9 ng/mL) after initial radiation therapy. ⁶⁸Ga-PSMA11 DMI images (A, MIP; B1-B3, axial PET, CT and fused PET/CT images, respectively) show focal uptake in a 10 mm lung nodule (arrow), not seen in the D690 scan (C1-C3, axial PET, CT and fused PET/CT images, respectively; D, MIP). This lesion has been previously diagnosed by ⁶⁸Ga-PSMA11 PET/CT and ADT was initiated 4 months prior to recent ⁶⁸Ga-PSMA11 imaging which showed a decrease in size as response to treatment as well as a decrease in PSA. We therefore ruled the lung nodule as PC metastasis.

Fig. 3

69-year-old patient with BCR PC (PSA 4.2 ng/mL) after initial radical prostatectomy. ⁶⁸Ga-PSMA11 DMI images (A, MIP; B1-B3, axial PET, fused PET/CT images and CT, respectively) show focal uptake in a 4 × 3 mm left pelvic lymph node (arrow), which was missed in images from D690 scanner (C1–3, axial PET, fused PET/CT images and CT, respectively; D, MIP). This lesion was also seen in a previous research ⁶⁸Ga-RM2 PET/MRI. Disease management did not change as the patient refused recommended RT.