Abstract
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Objectives Current methods of imaging advanced prostate cancer are nonspecific and better molecular imaging probes are sought. 18F DCFBC is a radiolabeled PET agent that binds with high affinity to PSMA, which is highly expressed in almost all prostate cancers. Identifying disease in soft tissue and bone with one tracer is appealing. We preliminarily compare the uptake of 18F DCFBC in bone with 18F NaF in prostate cancer patients with metastatic disease.
Methods Subjects undergo 2 separate 18F DCFBC imaging sessions, one at baseline, and then at 4-6 months. PET/CT images are performed at 1 and 2 hours after IV injection of 8 mCi 18F DCFBC. Patients also undergo a whole body 18F NaF scan within 3 weeks of each 18F DCFBC. Patients receive 3 mCi 18F NaF IV bolus and undergo whole body imaging 1 hour post injection. PSA levels are obtained at the time of 18F DCFBC imaging.
Results 6 patients with known bone metastasis were imaged. 13 bone lesions with focal 18F NaF uptake were compared to 18F DCFBC. 3 patients (5 lesions) had no visually significant focal uptake on DCFBC. NaF SUV uptake in these 5 lesions ranged from 2.8-15.7 and PSA ranged from .14-42.88 ng/ml. 2 of these patients were on androgen deprivation therapy (ADT.) 3 patients (8 lesions) had visually distinct focal uptake on both 1 and 2hr DCFBC images corresponding to focal 18F NaF uptake. DCFBC SUV in these lesions at 1hr ranged from 1.2-8.9 and at 2hrs, SUV ranged from .99-9.4. NaF SUV focal uptake ranged from 14.4-58.6 and PSA ranged from .28-4379 ng/ml. 2 patients were on ADT.
Conclusions 18F NaF uptake in bone metastasis does not necessarily correspond to focal 18F DCFBC uptake. Mechanisms of tracer uptake and tumor biology likely factor in the discrepant activity. Further investigation at the follow-up period and more patients will hopefully provide further insight. 18F DCFBC may provide new information on the expression of PSMA in this cancer and its role in tumor evolution.