11C-acetate PET in the early evaluation of prostate cancer recurrence

Purpose: The first aim of the study was to investigate the diagnostic potential of C-11-acetate PET in the early detection of prostate cancer recurrence. A second aim was the evaluation of early and late PET in this context. Methods: The study population comprised 32 prostate cancer patients with early evidence of relapse after initial radiotherapy ( group A) or radical surgery ( group B). The median PSA of group A ( n=17) patients was 6 ng/ml ( range 2.6 - 30.2) while that of group B ( n= 15) was 0.4 ng/ ml ( range 0.08 - 4.8). Pelvic-abdominal-thoracic PET was started 2 min after injection of C-11-acetate and evaluated after fusion with CT. Results: Group A: Taking a SUVmax >= 2 as the cut-off, PET showed local recurrences in 14/17 patients and two equivocal results. Distant disease was observed in six patients and an equivocal result was obtained in one. Endorectal MRI was positive in 12/12 patients. Biopsy confirmed local recurrence in six of six (100%) patients. PET was positive in five of the six patients with biopsy-proven recurrences, the result in the remaining patient being equivocal. Group B: Among the 15 patients, visual interpretation was positive for local recurrences in five patients and equivocal in four. One obturator lymph node was positive. Endorectal MRI was positive in 11/15 patients and equivocal in two. Positional correlation of positive/equivocal results on PET and endorectal MRI was observed in seven of nine patients. PSA decreased significantly after salvage radiotherapy in 8/14 patients, providing strong evidence for local recurrence. PET of the eight patients responding to RT was positive in three and equivocal in two. Conclusion: C-11-acetate PET was found to be valuable in the early evaluation of prostate cancer relapse. Optimising scanning time and use of modern PET-CT equipment might allow further improvement.