A comparison between two image reconstructions on the measures of prostate-specific membrane antigen-positive tumor volume in 18 F-PSMA-JK-7-PET/computed tomography.

Objectives: Tumor volume in prostate-specific membrane antigen (PSMA-TV)-PET/computed tomography (CT) has shown an emerging impact for prognosis and response evaluation in patients with prostate cancer. We evaluated the robustness of different PSMA-TV delineation methods.

Materials and methods: A total of 40 18 F-JK-7-PSMA-PET/CT performed on the same scanner were analyzed. PSMA-TV measurements were performed using a standardized uptake value of 4.0 as a fixed threshold (T1), 41% of the single hottest voxel as an adaptive threshold (T2), and a liver-specific threshold (T3) for delineation in two reconstruction methods [four iterations and 12 subsets (R1) and three iterations and 21 subsets while applying a point spread function and a time-of-flight algorithm (R2)]. Differences between the segmentation thresholds in R1 and R2 were gathered and tested for statistical significance.

Results: PSMA-TV differed significantly between R1Tx and R2Tx for individual segmentation thresholds, with PSMA-TV in R2 being significantly smaller than in R1 using the same segmentation method. Comparing the differences in PSMA-TV between R1 and R2 reconstruction between the three separate segmentation thresholds showed significantly larger absolute volume differences for T2 compared with T3 and significantly larger relative volume differences for T2 compared with T1 and T3.

Conclusion: Reconstruction settings greatly influence the measurement of PSMA-TV, regardless of the segmentation threshold chosen; however, our results indicate that the fixed thresholds (T1 and T3) are less susceptible to reconstruction-induced volumetry effects than a relative threshold.