Evaluation of primary prostate cancer using ¹¹C-methionine-PET/CT and ¹⁸F-FDG-PET/CT

The objective of this study was to evaluate the capability of ¹¹C-methionine (MET)-PET/CT and ¹⁸F-2-deoxy-2-fluoro-d-glucose (FDG)-PET/CT to diagnose primary prostate cancer using recently developed Gemini TF PET/CT (Philips Healthcare, Cleveland, OH).

Twenty men who had been referred for a diagnostic work-up for prostate cancer were enrolled in this study. MET- and FDG-PET/CT by high-resolution mode were carried out on the same day prior to prostate biopsy and each maximum standardized uptake value (SUVmax) was compared with the pathological findings. The regions of interest (about 100 mm² small round) were placed at standard 6 points of the peripheral zone and 4 points in the apex of the transitional zone in cases that had undergone biopsy of the internal gland. We summed two scores if a specimen had inhomogeneous Gleason scores (e.g. GS 7; 4 + 3) and doubled the score when the Gleason score was the same (e.g. GS 8; 4 × 2). We divided the tumors into three groups. If the summed Gleason score of the specimens was 5 or less, they were grouped as NG (no grade with the Gleason score). If the summed Gleason score was 6 or 7, the tumors were defined as LG (low Gleason score group), and if the summed Gleason score was 8, 9 or 10, the tumors were classified as HG (high Gleason score group). The mean SUVmax was calculated and one-way analysis of variance or Kruskal–Wallis test and the Tukey post hoc test were performed for statistical comparisons. The capabilities of MET and FDG for diagnosing prostate cancer were evaluated through analysis of the area under the curve of the receiver operating characteristic (ROC) curve. The cut-off levels of SUVmax for the highest accuracy were determined by the results of the ROC analysis, and the sensitivity, specificity and accuracy were calculated.

The PET images, obtained with Gemini TF PET/CT, allowed visual identification of anatomical locations within the prostate gland. Among the mean SUVmax of MET, FDG early phase and FDG delayed phase, the differences between NG and HG were all statistically significant (P < 0.01). With MET the difference between NG and LG was also significant (P < 0.05). And for the elevation rate from FDG early to delayed phase, the difference between NG and HG was significant (P < 0.05). The cut-off SUVmax, sensitivity, specificity, accuracy for distinguishing between NG and LG + HG by MET, FDG early and delayed phase were 3.15/78.7/75.6/78.3, 2.81/61.7/80.0/70.7 and 3.00/62.8/78.9/70.7, respectively. And the same factors between NG + LG and HG were 3.76/70.1/89.7/82.6, 2.88/70.1/82.9/78.3 and 3.47/62.7/86.3/77.7, respectively.

In terms of the capability to diagnose prostate cancer of high Gleason score (≥8), there was no significant difference between MET and FDG. MET appears to be useful for detecting prostate cancer of both low and high Gleason score.