The usefulness of fractal analysis in FDG-PET/CT images for diagnosing therapeutic effect of non-small cell lung cancer.

287 Purpose: Fractal dimension (D value) is an index of self-similarity and is considered to be useful indicator for homogeneity of tumor FDG uptake. There is a possibility that therapeutic effect can be divided into subgroups from the change of D value before and after cancer treatment. The study was done to investigate the usefulness of fractal analysis in FDG-PET/CT for diagnosing the therapeutic effect in non-small cell lung cancer (NSCLC). Materials and Methods: Seventy-two patients with NSCLC (47men and 25 women, age 59-84, mean age 65.5±10.7) were analyzed retrospectively. FDG-PET/CT examinations were done in the all patient before and after chemotherapies of various regimens. The chemotherapeutic effects were evaluated based on the change of FDG-uptake by PERCIST criterion. We also evaluated chemotherapeutic effects by the change of D values obtained by two kinds of Fractal analysis (Box counting method and Pixel counting method) on the FDG-PET MIP images. In the Fractal analysis, we calculated ΔD which is determined by the formula (D value of post-therapy) / (D value of pre-therapy) as parameters for evaluating the chemotherapeutic effect. Finally, we compared ΔD values among PMR, SMD and PMD group diagnosed by PERCIST criteria. Results: The values of ΔD were significantly higher in the PMD group compared with those in the PMR group. Namely, 1.41 vs. 0.83 by the evaluation with Box counting method and 2.78 vs. 0.84 by the evaluation with Pixel counting method. After chemotherapy, most of the PMR cases came to show the inhomogeneous FDG uptake and the most of PMD cases came to show the homogeneous FDG uptake. As for SMD group they showed various pattern and the values of ΔD were 0.96 by Box counting method and 2.38 by Pixel counting method. The association between the change of glucose metabolism and the change of homogeneity in FDG accumulation was suggested. Conclusions: In NSCLC before and after cancer therapy, fractal dimension decreased in the PMR group and tended to increase in PMD group. The change of fractal dimension (ΔD) by Box counting method or Pixel counting method in FDG uptake will be supplemental useful parameter for diagnosing cancer therapeutic effect in NSCLC