Texture analysis for FMISO PET/CT in oncology patients receiving extra-beam radiation therapy

Objectives F-18-fluoromisonidazole (FMISO) PET/CT is one of the useful tools that have been investigated to visualize hypoxic status in tumors. The aim of this study was to clarify the feasibility of texture analysis of tumor hypoxia as well as absolute levels of FMISO uptake on FMISO PET/CT in association with local control by radiation therapy (RT).

Methods This study involved 18 patients (pts) with neoplasms (head and neck 8, esophagus 5, anus 2, lung 2, uterus 1) who underwent RT and FMISO PET/CT. FMISO PET/CT scans were conducted at the baseline and at 20 Gy of RT; each patient received iv injection of FMISO (7.4 MBq/kg) and underwent PET/CT at 180 min. Regions of interest were placed on tumors to measure SUVs of FMISO. Additionally, texture analyses dealt with the heterogeneity indices of skewness, kurtosis, and another heterogeneity index of area under curve of cumulative SUV histogram (AUC-CSH). And a larger skewness, a larger kurtosis, and a smaller AUC-CSH were considered to indicate a higher heterogeneity. Pts were categorized into CR and non-CR (PR+NC+PD) groups, and the parameters were compared between the two groups by Mann-Whitney’s U test.

Results Pts received chemoradiation therapy (n=17, 42-70 Gy) or RT alone (n=1, 64 Gy). Nine pts reached CR, while 9 did not. Reduced FMISO SUVs were observed at 20Gy as compared to before RT, which might correspond to reoxygenation. CR group showed statistically significant lower SUVmax and kurtosis and a tendency of lower skewness and higher AUC-CSH.

Conclusions Texture analysis of intratumoral FMISO distribution was feasible. Correlation of heterogeneity and therapeutic response should be clarified in further studies. A lower absolute level of FMISO accumulation before RT might be predictive of a better therapeutic response.