Localized prostate cancer detection with 18F FACBC PET/CT: comparison with MR imaging and histopathologic analysis

Abstract

Purpose: To characterize uptake of 1-amino-3-fluorine 18-fluorocyclobutane-1-carboxylic acid ((18)F FACBC) in patients with localized prostate cancer, benign prostatic hyperplasia (BPH), and normal prostate tissue and to evaluate its potential utility in delineation of intraprostatic cancers in histopathologically confirmed localized prostate cancer in comparison with magnetic resonance (MR) imaging.

Materials and methods: Institutional review board approval and written informed consent were obtained for this HIPAA-compliant prospective study. Twenty-one men underwent dynamic and static abdominopelvic (18)F FACBC combined positron emission tomography (PET) and computed tomography (CT) and multiparametric (MP) 3-T endorectal MR imaging before robotic-assisted prostatectomy. PET/CT and MR images were coregistered by using pelvic bones as fiducial markers; this was followed by manual adjustments. Whole-mount histopathologic specimens were sliced with an MR-based patient-specific mold. (18)F FACBC PET standardized uptake values (SUVs) were compared with those at MR imaging and histopathologic analysis for lesion- and sector-based (20 sectors per patient) analysis. Positive and negative predictive values for each modality were estimated by using generalized estimating equations with logit link function and working independence correlation structure.

Results: (18)F FACBC tumor uptake was rapid but reversible. It peaked 3.6 minutes after injection and reached a relative plateau at 15-20 minutes (SUVmax[15-20min]). Mean prostate tumor SUVmax(15-20min) was significantly higher than that of the normal prostate (4.5 ± 0.5 vs 2.7 ± 0.5) (P < .001); however, it was not significantly different from that of BPH (4.3 ± 0.6) (P = .27). Sector-based comparison with histopathologic analysis, including all tumors, revealed sensitivity and specificity of 67% and 66%, respectively, for (18)F FACBC PET/CT and 73% and 79%, respectively, for T2-weighted MR imaging. (18)F FACBC PET/CT and MP MR imaging were used to localize dominant tumors (sensitivity of 90% for both). Combined (18)F FACBC and MR imaging yielded positive predictive value of 82% for tumor localization, which was higher than that with either modality alone (P < .001).

Conclusion: (18)F FACBC PET/CT shows higher uptake in intraprostatic tumor foci than in normal prostate tissue; however, (18)F FACBC uptake in tumors is similar to that in BPH nodules. Thus, it is not specific for prostate cancer. Nevertheless, combined (18)F FACBC PET/CT and T2-weighted MR imaging enable more accurate localization of prostate cancer lesions than either modality alone.

Figure 1a:

(a) Mean time-activity curves for normal prostate, tumor and, BPH. ¹⁸F FACBC retention is seen throughout the time course in normal prostate tissue, tumors, and BPH. (b) The tumor-to–normal prostate uptake ratio (estimate of tumor-specific uptake) is more constant between 15 and 25 minutes after injection.

Figure 1b:

(a) Mean time-activity curves for normal prostate, tumor and, BPH. ¹⁸F FACBC retention is seen throughout the time course in normal prostate tissue, tumors, and BPH. (b) The tumor-to–normal prostate uptake ratio (estimate of tumor-specific uptake) is more constant between 15 and 25 minutes after injection.

Figure 2:

Images in a 56-year-old man with a serum PSA level of 31.5 ng/mL. A, T2-weighted MR image, B, apparent diffusion coefficient map of DW MR imaging, and, C, DCE MR image show a low-signal-intensity focus in the left midtransitional zone (arrows), which shows ¹⁸F FACBC uptake on, D, a PET/CT image (SUV_{max [15–20 min]} = 6.5) (arrow). E, Histopathologic image enabled confirmation of a Gleason 3+4 cancer focus (arrow) (inked in green on the left).

Figure 3:

Images in a 57-year-old man with a serum PSA level of 3.81 ng/mL. A, T2-weighted MR image and, B, apparent diffusion coefficient map of DW MR imaging show a low-signal-intensity focus in the right midcentral gland (arrows), which shows ¹⁸F FACBC uptake on, C, a PET/CT image (SUV_{max (15–20 min)}, 6.8) (arrow). D, Histopathologic image enabled confirmation of a BPH nodule but not a prostate tumor (black arrow) (inked in brown); a small tumor focus (green arrow) (inked in green) was also present in the left transitional zone but was not seen at MR imaging or ¹⁸F FACBC PET/CT.