Publication

Abstract :

Purpose : The standard imaging used for delineation of dominant intraprostatic lesion (DIL) is multiparametric MRI (mpMRI). The use of biologic imaging such as Ga-68 prostate-specific membrane antigen (PSMA) PET-computed tomography (PET-CT) for this purpose is being explored in view of increased sensitivity of this modality and the associated ease of delineation.

Materials and methods : The primary objective of the study was to compare the autogenerated volumes of the DIL in Ga-68 PSMA PET-CT with the standard volume delineated in mpMRI. Twenty patients with biopsy-proven untreated prostatic adenocarcinoma were included. Multiple percentages of the maximum standardized uptake value (%SUVmax) were used to autogenerate DIL volumes in Ga-68 PSMA PET-CT and these volumes were numerically matched with the consensus DIL volume in mpMRI. PSMA tumor volume (PSMA-TV) and total lesion PSMA (TL-PSMA) were also calculated for each lesion.

Results : Median volume of DIL in mpMRI was 4 cm³ (interquartile range, IQR = 2.5–7.6 cm³). The IQR for interobserver variability was 0.5–2.5 cm³. Median SUVmax of the DIL was 14.1 (IQR = 10.2–22.3). Median %SUVmax corresponding to mpMRI volume was 41% of SUVmax (IQR = 34–55%). There was a strong negative correlation between MRI volume and %SUVmax (r = −0.829, P < 0.001). There was a significant correlation between TL-PSMA and prostate-specific antigen (r = 0.609, P = 0.004).

Conclusions : The median DIL volume was 4 cm³ and median %SUVmax corresponding to MR volume of DIL was 41%. A strong inverse relationship is found between mpMRI-defined DIL volume and the %SUVmax which generates similar volume in Ga-68 PSMA PET-CT. TL-PSMA could be a quantitative biomarker for tumor load and prognosis.