Image-guided PO2 probe measurements correlated with parametric images derived from 18F-fluoromisonidazole small-animal PET data in rats.
The purpose of this study is to use dynamic [18F]fluoromisonidazole ([18F]FMISO) positron emission tomography (PET) to compare estimates of tumor hypoxic fractions (HFs) derived by tracer kinetic modeling, tissue-to-blood ratios (TBR), and independent oxygen (pO2) measurements. BALB/c mice with EMT6 subcutaneous tumors were selected for PET imaging and invasive pO2 measurements. Data from 120-min dynamic [18F]FMISO scans were fit to two-compartment irreversible three rate constant (K 1, k 2, k 3) and Patlak models (K i). Tumor HFs were calculated and compared using K i, k 3, TBR, and pO2 values. The clinical impact of each method was evaluated on [18F]FMISO scans for three non-small cell lung cancer (NSCLC) radiotherapy patients. HFs defined by TBR (≥1.2, ≥1.3, and ≥1.4) ranged from 2 to 85 % of absolute tumor volume. HFs defined by K i (>0.004 ml min cm−3) and k 3 (>0.008 min−1) varied from 9 to 85 %. HF quantification was highly dependent on metric (TBR, k 3, or K i) and threshold. HFs quantified on human [18F]FMISO scans varied from 38 to 67, 0 to 14, and 0.1 to 27 %, for each patient, respectively, using TBR, k 3, and K i metrics. [18F]FMISO PET imaging metric choice and threshold impacts hypoxia quantification reliability. Our results suggest that tracer kinetic modeling has the potential to improve hypoxia quantification clinically as it may provide a stronger correlation with direct pO2 measurements.