F-18 labelled 3’-deoxy-3’-fluorothymidine (FLT) positron emission tomography (PET) imaging in patients with advanced pancreatic ductal adenocarcinoma: proof-of-concept reproducibility sub-analysis.
Session type: Oral
The thymidine analogue FLT is transported and phosphorylated in proliferating cells. FLT tumour uptake correlates with proliferation.
Advanced pancreatic ductal adenocarcinoma (PDAC) patients with target lesion >2cm due to start chemotherapy were eligible. Dynamic FLT PET/CT scanning was performed over 60min, before starting chemotherapy (baseline scan, BS). Intra-patient reproducibility was explored by a second FLT scan within 7 days of BS and before chemotherapy (reproducibility scan, RPS). Lesions were manually delineated by two independent radiologists for determination of inter-radiologist concordance. FLT uptake in the primary tumour and metastases was quantified as standardised uptake value (SUV, mean and max) over 45-60min.
Of the 21 patients consented 18 were scanned, all with primary tumour in situ and 83% with distant metastases (60% in liver). Thirty-five FLT scans were acquired for the whole study, 21 scans were analysed for this reproducibility sub-analysis (17 BS, 4 RPS) and 27 lesions delineated. At baseline, median SUVmean and SUVmax were 1.9 (95%CI 1.8-2.1) and 5.9 (95%CI 4.6-7.8), respectively, for the primary (n=17) and 4.6 (95%CI 3.7-5.2) and 8.9 (95%CI 8.2-10.5), respectively, for metastatic lesions (n=10; 9 liver, 1 lymph node). Intra-patient reproducibility between BS and RPS was good (all lesions; n=8): mean change and standard deviation (SD) of test-retest differences and Lin’s concordance coefficient (LCC) for SUVmean (mean change -5.4%; SD 9.8%; LCC 0.947, p<0.001) were superior to SUVmax (mean change 7.9%; SD 19.2%; LCC 0.642, p<0.001). The reproducibility achieved by the second radiologist was similar (6 lesions): SUVmean (mean change -10.3%, SD 12.8%; LCC 0.534, p=0.005) and SUVmax (mean change 4.7%, SD 14.5%; LCC 0.826, p<0.001). Inter-radiologist concordance was assessed by comparing 12 lesions (8 scans; 4 BS, 4 RPS): LCC for SUVmean and SUVmax were 0.635 (p<0.001) and 0.489 (p=0.019), respectively.
FLT-PET is feasible and reproducible (intra-patient and inter-radiologist) in patients with advanced PDAC.