18F-FACBC Compared With 11C-Choline PET/CT in Patients With Biochemical Relapse After Radical Prostatectomy: A Prospective Study in 28 Patients

Abstract

Introduction

The aim of our study was to compare the detection rate of anti-3-18F-FACBC PET/CT in comparison with 11C-choline PET/CT in the evaluation of disease recurrence of PCa after radical prostatectomy.

Patients and Methods

Twenty-eight consecutive patients with biochemical relapse after radical prostatectomy were submitted to anti-3-18F-FACBC PET/CT and 11C-choline PET/CT to evaluate the site of disease recurrence. Androgen deprivation therapy was avoided in all cases. The primary end point was the overall detection rate of the 2 radiotracers. A patient-based analysis and a lesion-based analysis was performed. The target to background ratio (TBR) of each lesion was reported.

Results

At the time of PET scan, mean age was 67 years and mean prostate specific antigen (PSA) relapse was 2.9 ng/mL (range: 0.2-14.6). In patient-based analyses, 11C-choline PET/CT was positive in 5 patients and negative in 23 (detection rate = 17.8%) and anti-3-18F-FACBC PET/CT was positive in 10 patients and negative in 18 (detection rate = 35.7%). All lesions that were positive using 11C-choline were positive using anti-3-18F-FACBC PET/CT but with the latter radiotracer, 11 (61.1%) additional tumors were identified including 5 (17.8%) additional patients. The TBR of anti-3-18F-FACBC was greater than 11C-choline in 15 of 18 lesions, confirming a better image quality and contrast.

Conclusion

This preliminary study demonstrated that the detection rate of anti-3-18F-FACBC PET/CT is greater in comparison with 11C-choline, with approximately 20% of additional patients and approximately 60% additional lesions detected. Further studies, however, are required to assess the exact added value of this new tracer.

Introduction

Approximately 40% of all patients who undergo radical treatment for localized prostate cancer (PCa) develop biochemical relapse (BCR) during their lifetime but only 10% to 20% of them will show clinically detectable recurrences. Current imaging techniques have some potential but many limits are yet encountered in the localization of disease relapse.1, 2 Transrectal ultrasound (TRUS) has low accuracy in the detection of local recurrence. Bone scan and abdominal computed tomography (CT) or magnetic resonance imaging are not useful in the detection of disease relapse unless the prostate specific antigen (PSA) is greater than 10 to 20 ng/mL. Today, positron emission tomography (PET)/CT might visualize the site of recurrence earlier, with better accuracy than conventional imaging and in a single step.³ Choline is the most studied and promising radiotracer in PCa. The principal advantage of choline PET/CT is its ability to visualize disease relapse even in the presence of a low PSA level. Choline PET/CT has also opened new therapeutic frontiers that were not imaginable in the past, such as salvage lymphadenectomy or lymph node (LN) irradiation with tomotherapy in the presence of pelvic or retroperitoneal recurrence. It has been reported that choline PET/CT allows changing the therapeutic strategy (from palliative to curative treatment and vice-versa) in approximately 20% of cases. Furthermore, choline PET/CT is now Food and Drug Administration-approved in the United States, but only when other imaging techniques are noninformative. The main limit of choline PET/CT is the low resolution of scanners (approximately 5 mm); moreover, not all PCa lesions show positive uptake of choline. In fact, when a suspected lesion is found using choline PET/CT, nearly twice as many metastases are present.⁴ To overcome these limits, new radiotracers for PET/CT are now being evaluated worldwide. In recent years, a synthetic L-leucine analogue (the anti-1-amino-3-18F-fluorocyclobutane-1-carboxylic acid, in brief: anti-3-18F-FACBC) has been proposed as a possible alternative radiopharmaceutical to detect PCa.⁵ Anti-3-18F-FACBC uptake is related to the functional activity of 2 different amino acid transporters (amino acid system of alanine, serine, cysteine, and independent “L” large-neutral amino acid transport system) and the distribution of the tracer in the body is more favorable than choline (mild and diffuse uptake in the bone marrow and negligible uptake in the kidney with no activity in the urinary tract). This might reduce the risk of having small sites of disease relapse masked by a physiological presence of the tracer excreted in the urinary tract or in bones. Last but not least, the synthesis of anti-3-18F-FACBC is faster and the half-life is longer (109 minutes), rendering the radiotracer more available. From a clinical point of view, the first clinical studies showed very promising and reproducible results: preliminary reports of anti-3-18F-FACBC PET/CT compared with choline PET/CT or 111In-capromab pendetide single photon emission CT (SPECT)/CT demonstrated the improvement in detection rate of approximately 20% to 40%. Furthermore, in the recent studies, anti-3-18F-FACBC PET/CT has been demonstrated to not only visualize PCa, but also to allow differentiation between PCa and inflammation or benign lesion, rendering the anti-3-18F-FACBC PET/CT a possible radiotracer of the future for PCa.6, 7, 8, 9 The aim of the present study was to compare the detection rate of anti-3-18F-FACBC PET/CT in comparison with 11C-choline PET/CT in the evaluation of disease recurrence of PCa in patients with BCR after radical prostatectomy.