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Only a minority of patients with relapsing PCa appear to benefit from AC-PET for guiding potential local treatment. False-positive results show that factors other than tumour metabolism induce increased AC uptake. The time free of recurrence after local treatment was shorter than expected.

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e16003 Background: Patients with rising PSA levels after definitive local therapy of prostate carcinoma often present a diagnostic dilemma . A local recurrence or metastatic lymph node lesions would be amenable to additional local therapy. In this prospective study the effectiveness of 11C-acetate PET (AC-PET) matched with corresponding CT scans in patients with PSA relapse were evaluated. Methods: 103 patients (mean age 70.87 years; range 56 – 90 years) with histologically confirmed adenocarcinoma of the prostate were enrolled in this study because of rising PSA values following RP (n = 97) or radiotherapy (n=6). Whole-body PET images were obtained after iv - administration of 1,000 MBq of 11C-acetate. A CT scan from the neck to the pelvic floor was performed additionally. An image overlay of corresponding CT and PET scans was done. By using attenuation corrected PET data, standardized uptake value (SUV) was calculated, cut-off 2. Results: Out of 103 patients n=42 were AC-PET positive. PSA level in 16 of this subset was between 0.5 and 1.45 ng/mL (mean value 1.14 ng/mL), in 16 patients between 2.7 and 9.01 ng/mL, and 7 patients had a PSA distribution between 13.4 and 30.5 ng/mL, respectively. Analysing the AC-PET positive patients, in 16/42 AC-PET demonstrated hypermetabolic lymphnode lesions, in 10/16 metastatic lesions were histopathologically confirmed, in the remaining 6 unspecific inflammatory tissue alterations were identified. In 9 patients with corresponding AC-PET and CT scans radiotherapy of proven lymphnode metastases was performed followed by decreasing PSA level. 23/42 patients were treated with hormone manipulation (21/23) or chemotherapy (2/23). Combining the patients having undergone surgery and radiotherapy (n=25) there were 19/25 true positive in terms of AC-PET, in 13 / 25 PSA level was < 2.0 ng/mL. Conclusions: Although AC-PET seems to be a promising tool in the detection of recurrent prostate cancer even with PSA levels < 2 ng/ml, false positive patients with a different metabolism marked by 11C-acetate decrease the specificity of the approach. Thus there is still a need for a more specific tracer development.

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