Abstract
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Objectives Tumor/blood ratio analysis for FMISO-PET is major semi-quantitation method for tumor hypoxia. However, it is sometimes unstable to evaluate metabolism using venous blood sampling. There is a report which suggests the correlation between tumor/muscle ratio of FMISO-PET and pO2 Polarography. The aim of this study was to compare reproducibility of semi-quantification based on muscle activity and that based on blood activity.
Methods Seven patients with untreated head and neck cancer underwent two FMISO-PET studies with 2 days interval. They were confirmed that they did not have any abnormality in brain and heart. Patients underwent 3 minutes scan using PET/CT scanner at 4 hours after FMISO injection (400MBq). Blood sampling was performed following scan. Region of interest was put on brain, heart, and posterior cervical muscle of PET/CT images. Brain/muscle ratio (BMR), brain/blood ratio (BBR), heart/muscle ratio (HMR), heart/blood ratio (HBR) were calculated, and the difference of these parameters between two PET studies were compared.
Results BMR was 0.82 ± 0.04 (mean ± SD), and BBR was 0.79 ± 0.17. The difference of BMR (4.6 ± 3.2 %, range 0.4 - 9.1 %) was significantly smaller than that of BBR (14.0 ± 10.0 %, range 5.5 - 32.4 %, p < 0.01), suggesting high reproducibility of muscle activity. HMR was 0.95 ± 0.08, and HBR was 0.92 ± 0.20. The difference of HMR (2.9 ± 2.5 %, range 0.7 - 6.4 %) was also significantly smaller than that of HBR (16.8 ± 7.9 %, range 3.5 - 27.1 %, p < 0.01), supporting high reproducibility of muscle activity.
Conclusions These data indicated significantly higher reproducibility of semi-quantitation method based on muscle activity than that based on blood activity. Semi-quantification based on muscle activity may be more suitable for hypoxic evaluation