Reproducibility of ¹⁸FMISO PET kinetic parameters in NSCLC

Objectives Kinetic modeling for the assessment of tumor response demands an understanding of the repeatability of the underlying quantitative parameters in the absence of therapy.Establishing whether changes in parameter values during treatment reflect changes in underlying biology rather than fluctuations is crucial. In this study we determine reproducibility of kinetic parameters (KP) for ¹⁸F-fluoromisonidazole (¹⁸FMISO), deduced from kinetic modeling of dynamic PET (dPET) images.

Methods 3 patients diagnosed with non-squamous non-small cell lung cancer (NSCLC) underwent 2 free-breathing (3 days apart),pre-treatment ¹⁸FMISO dPET.Patients were injected with ~10mCi FMISO.A repeat injection and 2nd scan were performed 3 d later. Data for dPET were acquired as follows:12x10 sec,10x1min,and 5x5min (37m).Two 10min frames were acquired at 90±10min and 150±10min,respectively. Data were reconstructed in 128x128x47 matrices,and 700mm FOV.Pixel-wise and average time-activity curves (TAC) were obtained inside VOIs placed over each lesion.Input functions were derived from VOIs over the aorta for each session.Modeling was performed on all TACs with a 2-tissue,3 compartment (plasma,free,bound) model with irreversible binding (k4=0).Reproducibility was assessed for all KP (K1,Vd,k3,Vb) by calculating percent change between 1st and 2nd scans for: 1) KPs averaged over all pixels and 2) KPs from average TACs.

Results The mean values of the KPs for the two pre-treatment data sets are: k3) 0.005,0.0055,K1) 0.17,0.13,Vd) 0.73,0.68,Vb) 0.098,0.164. When comparing KPs averaged over the pixels in VOI,k3 and Vd the % differences are ≦10% and 6.8% respectively,whereas K1 and Vb,have larger % differences ≦38.8% and 23.9% respectively.KPs calculated from average VOI TACs,the % difference in the parameters are 35.1,6.8,32.2,28.8% for k3,Vd,K1 and Vb respectively.

Conclusions This study shows the reproducibility of performing kinetic analysis of lung lesions during respiration. In future,the same method will be used to compare results for breath-holding. These are expected to have higher repeatability.