Detection of intra-pelvic versus extra-pelvic lesions with Carbon-11 Acetate Positron Emission Tomography/Computed Tomography imaging in the evaluation of recurrent prostate cancer – Interim results from the AMIC-AC-001 clinical study.

Fabio Almeida MD (Presenter), Steven E. Finkelstein MD, Larry L. Bans MD, Mark Scholz MD, Richard Lam MD, Jeffery Turner MD

 

Purpose: A rising prostate specific antigen (PSA) after definitive therapy possess a significant problem, as it represents a large group of prostate cancer (PCa) patients.  These patients with “biochemical relapse” often have the absence of sufficiently detectable disease on standard imaging studies, thereby limiting treatment options.

Methods: 373 CA PET/CT studies were reviewed in an ongoing single site FDA/IND clinical study (NCT01304485). Male patients with histologically proven PCa and biochemical recurrence (BCR) were imaged. Imaging was performed from vertex through thighs on an integrated PET/CT scanner injected with 740-1480 MBq C11-Acetate with imaging 3 to 7 minutes post injection. Detected lesions were defined as moderate to intense focal areas of increased CA metabolic activity over background in the prostate, prostatic bed, nodes and bone. 

Results:  PSA ranged from 0.2 – 148 ng/mL (mean 6.3, median 2.7). The overall detection rate was 87%. At various PSA subgroups the detection rates were: 0.2-0.4 = 50%, 0.41 – 1.0 = 77%, >1.1 90%. True positive (TP) studies were defined as those with positive biopsy, confirmatory imaging or where radiotherapy (RT) was directed at the detected site with a resultant drop in PSA.  145 patients have thus far met criteria for TP analysis, with a PPV of 94%. Focal lesions were detected only in the prostate or bed in 28% (post prostatectomy [RP]: 32%, post RT: 31%, post RP-RT: 11%). In 24% of studies, only focal pelvic nodal lesions were detected (RP:32%, RT:13%, RP-RT: 41%). Lesions where detected in both the prostate/bed and pelvic nodes in 7% of studies. Metabolic lesions were detected in both the pelvis and abdomen in 7% and isolated to abdominal nodes in 3%. Bone lesions were found in 28% of the studies (71% in bone only and 29% with soft tissue lesions). In 3%, lesions where detected in the other areas such as the lungs, mediastinal nodes or in supraclavicular nodes (particularly on the left).

Conclusion: In patients with BCR of PCa, CA PET/CT imaging demonstrates a high detection rate and PPV for localizing the site of recurrence/metastasis. Particularly evident in this patient population is the high detection of locally recurrent and intra-pelvic nodal disease (59%), which may be amenable to additional focal therapy with a curative intent, such as additional surgical treatment, radiation or cryotherapy. CA PET/CT was also able to better identify those patients with distant metastases, whom would most benefit from systemic therapy.

 

CLINICAL RELEVANCE/APPLICATION: PCa recurrence after initial definitive treatment occurs in up to 40% of patients. Conventional imaging is of limited value in this patient population and CA PET imaging appears to help differentiate those with local-regional disease from distant metastasis.