Evaluation of [68Ga]Ga-PSMA PET/CT Images Acquired with a Reduced Scan Time Duration in Prostate Cancer Patients using the Digital Biograph Vision

Abstract

Aim: [68Ga]Ga-PSMA-11 PET/CT allows for a superior detection of prostate cancer tissue, especially in the context of a low tumor burden. Digital PET/CT bears the potential of reducing scan time duration / administered tracer activity due to, for instance, its higher sensitivity and improved time coincidence resolution. It might thereby expand [68Ga]Ga-PSMA-11 PET/CT that is currently limited by 68Ge/68Ga-generator yield. Our aim was to clinically evaluate the influence of a reduced scan time duration in combination with different image reconstruction algorithms on the diagnostic performance.Methods: Twenty prostate cancer patients (11 for biochemical recurrence, 5 for initial staging, 4 for metastatic disease) sequentially underwent [68Ga]Ga-PSMA-11 PET/CT on a digital Siemens Biograph Vision. PET data were collected in continuous-bed-motion mode with a mean scan time duration of 16.7 min (reference acquisition protocol) and 4.6 min (reduced acquisition protocol). 4 iterative reconstruction algorithms were applied using a time-of-flight (TOF) approach alone or combined with point-spread-function (PSF) correction, each with 2 or 4 iterations. To evaluate the diagnostic performance, the following metrics were chosen: (a) per-region detectability, (b) the tumor maximum and peak standardized uptake values (SUVmax and SUVpeak) and (c) image noise using the liver’s activity distribution.Results: Overall, 98% of regions (91% of affected regions) were correctly classified in the reduced acquisition protocol independent of the image reconstruction algorithm. Two nodal lesions (each ≤4 mm) were not identified (leading to downstaging in 1/20 cases). Mean absolute percentage deviation of SUVmax (SUVpeak) was approximately 9% (6%) for each reconstruction algorithm. The mean image noise increased from 13% to 21% (4 iterations) and from 10% to 15% (2 iterations) for PSF+TOF and TOF images.Conclusions: High agreement at 3.5-fold reduction of scan time in terms of per-region detection (98 % of regions) and image quantification (mean deviation ≤ 10 %) was demonstrated; however, small lesions can be missed in about 10% of patients leading to downstaging (T1N0M0 instead of T1N1M0) in 5 % of patients. Our results suggest that a reduction of scan time duration or administered [68Ga]Ga-PSMA-11 activities can be considered in metastatic patients, where missing small lesions would not impact patient management. Limitations include the small and heterogeneous sample size and the lack of follow-up.

Phantom-based acquisition time and image reconstruction parameter optimisation for oncologic FDG PET/CT examinations using a digital system

“…This is in line with a published clinical evaluation of 100 lesions, in which all lesions were detected at 60 s acquisition time, whereas at 30 s acquisition time single lesions were missed [34]. Moreover, comparable results indicating a threshold of 60 s per bed position were also obtained in phantom and clinical studies investigating 68 Ga-PSMA-11 PET/CT for imaging of prostate cancer patients [51,52].…”

Digitale Positronenemissionstomografie – Entwicklung, Detektortechnologie und Perspektiven

“…Analog hierzu konnte gezeigt werden, dass eine Reduktion der 68 Ga-PSMA-11 dPET Akquisitionszeit um einen Faktor von bis zu 3,5 möglich ist und die Detektionsrate pro anatomischer Region sowie die Quantifizierung trotzdem vergleichbar blieben. Es muss jedoch beachtet werden, dass kleine Läsionen bei der Reduktion der Scanzeit unter Umständen nicht erkannt werden können 20 . Gerade für die Bestimmung des Ganzkörper Tumorvolumens, das ein prädiktiver Biomarker für Patienten mit end-stage-Prostatakarzinom ist, könnte eine solche Reduktion der Akquisitionszeit bzw.…”