18F-fluciclovine (FACBC) PET/CT in residual or recurrent gliomas

Objectives Trans-1-amino-2-[18F]-fluorocyclobutane-carboxylic acid (fluciclovine, FACBC) is a synthetic leucine analogue mostly used as a PET tracer in prostate cancer. The aim of this study was to measure the uptake and calculate the tumor-to-background-uptake of fluciclovine (FACBC) on PET/CT in patients with suspected residual or recurrent gliomas.

Methods FACBC PET/CT was performed in 21 patients evaluated for residual or recurrent gliomas after surgery, external beam radiation and / or chemotherapy with temozolamide. The patients were 8 females and 13 males with mean age 57 (range 41-71). Sixteen patients had WHO histologic grade IV, 1 patient grade III, 3 patients grade II and 1 patient grade I. PET/CT imaging was performed on a Siemens mCT. Imaging was started on average 19 minutes after injection of 7 mCi FACBC with 6 min one bed acquisition. SUVmax of suspected tumor was compared to SUVmax of a reference region (background) of normal brain, and the tumor-to-background ratio (TBR) was calculated for all lesions. Image fusion of PET and MRI was performed for all patients. All images were read by an experienced nuclear medicine physician together with an experienced MR radiologist. The PET findings were compared to MRI and histopathology of surgical specimens. If surgery was not performed results were compared to follow-up studies and clinical outcome.

Results Median SUVmax of normal brain uptake was 0.6 (range 0.4-2.0). Median SUVmax of all lesions was 7 (range 1.7-27), while median TBR was 11.2 (range 2-45). Twelve patients were operated. Eight of these 12 had WHO histologic grade IV and 2 had grade III, median SUVmax was 10 (range 3.7-27), and median TBR 17 (4,7 - 45). Two patients did not show any sign of malignancy on histopathology. One of these patients with sign of radionecrosis had lesion SUVmax=5.2 and TBR=7.4. The tumor showed further progression on follow-up MRI, and the patient died 270 days after surgery. The other patient with benign histopathology assumed to be post-treatment inflammation had SUVmax=4.8 and TBR=9.6. Three patients with MRI findings highly suspicious for residual or recurrent disease were not found eligible for surgery. They had median SUVmax=6.7 and median TBR=11.2. The disease progressed in all three patients. Six patients had no evidence of residual or recurrent disease on MRI. Three of these patients died from tumor progression within 6 months. They had median TBR=2.8 (range 2-14.2). Two patients with FACBC uptake are still being followed up (TBR 2 and 5). One patient without increased FACBC uptake did not show any evidence of recurrent disease on follow-up MRI.

Conclusions Both SUVmax and TBR for residual or recurrent histologic high grade gliomas are high on FACBC PET/CT and higher than reported for 11C methionine and 18F FET. Thus, FACBC seems to be a promising tracer for detecting residual or recurrent gliomas, in particular high grade gliomas. FACBC PET/CT may possibly be used to supplement MRI in differentiation between tumor recurrence and pseudo-progression, but further studies are needed.