Evaluation of recurrent prostate cancer: Performance characteristics of Carbon-11 Acetate PET/CT imaging and Sodium-F18 PET/CT imaging for the detection of bony metastasis.  

Fabio Almeida MD (Presenter), Mark Scholz MD, Richard Lam MD, Jeffery Turner MD, Charles Myers MD

PURPOSE: This study compared C11-Acetate (CA) positron emission tomography (PET) and F18 Sodium Fluoride (F18-NaF) PET bone imaging for the detection of skeletal metastasis in men with biochemically recurrent prostate adenocarcinoma.  

METHOD AND MATERIALS: Men with prostate adenocarcinoma previously having had definitive therapy (radical prostatectomy, radiation therapy, or both) demonstrating a rising PSAs were evaluated retrospectively. CA PET studies where performed at our facility from 2011 – 2013 and F18-NaF PET imaging performed within 2 months was compared where available. Imaging studies were reviewed for the presence or absence of detected skeletal lesions, and for concordance in the number of detected lesions. Detection rates of soft tissue lesions in this patient subset was also evaluated on the CA PET studies in relation to the presence or absence of skeletal lesions. PSA kinetics were evaluated. 

RESULTS: 183 men (age 45 – 88, mean 69.6) were evaluated with CA PET and had a comparable F18-NaF PET. PSA ranged from 0.5 – 148ng/mL (median 2.5ng/mL). CA PET detected skeletal lesions in 59 (32%) of patients, whereas F18-NaF PET detected lesions in 75 (41%) patients. In 22 patients CA PET and F18-NaF where concordant, demonstrating a solitary bony lesion in 14 and multiple bony lesions in 7. 57 studies where found to be discordant. F18-NaF PET demonstrated bone lesions or additional bone lesions suggesting metastatic disease in 36 (20%) patients which were not seen on CA PET (median PSA 3.05ng/mL, median PSA doubling time 4 months). CA PET found bony lesions in 14 patients (8%) that where not present on the F18-NaF studies. There were 7 studies in which non-specific findings where present on the F18-NaF study that where negative on the CA PET and were therefor felt to be benign (degenerative changes, solitary rib foci or skull foci). In the studies positive for bony lesions, CA PET additionally identified soft tissue lesions in 31 (17%) patients. In 78 (42%) patients CA PET identified soft tissue lesions when no bone lesions where found on either the CA PET or F18-NaF studies (median PSA 2.36ng/mL, median PSA doubling time 5 months). These lesions were found to be in the pelvis (prostate,

prostate bed or regional nodes) in 61 (33%), extrapelvic regions in 6 (3%) and involving both pelvic and extrapelvic soft tissue site in 11 (6%). 

CONCLUSION: In this comparison study, results indicate that C11-Acetate PET and Sodium Fluoride PET are both useful and appear complimentary for the detection of skeletal metastasis in patients with biochemical recurrence of prostate cancer, but do show discordance in their detection rates. F18-NaF PET had an overall higher detection rate and found lesions in 20% of the studies that where not seen on CA PET.  CA PET alone found bone lesions in 8% and was able to help further characterize as benign, non-specific foci on the F18-NaF.  CA PET additionally was able to find soft tissue lesions in 78 studies negative for bony lesions, with the majority of these isolated to the pelvis and thereby possibly amendable to additional curative focal therapy. PSA kinetics where similar for those with bony lesions compared to those with only detected soft tissue lesions, and does not appear to guide a preference of one imaging study over the other in this patient population.

CLINICAL RELEVANCE/APPLICATION Prostate cancer recurrence after initial definitive treatment occurs in up to 40% of patients. Conventional imaging is of limited value in detection in early biochemical recurrence, thereby limiting treatment options.  C11-Acetate and F18 Sodium Fluoride PET appear to have a complimentary role in the evaluation of these patients.