Impact of hybrid PET/MR technology on multiparametric imaging and treatment response assessment of cervix cancer.

Abstract

Multimodal tissue characterization by combined MRI and PET has high clinical potential in the context of sub-target definition for dose painting and response assessment but its clinical exploration is yet limited. The aim of this study was to prove the potential and feasibility of hybrid PET/MRI to non-invasively measure tumor hypoxia, perfusion and microstructure at one stop in tumors of the uterine cervix during chemoradiotherapy. Ten cervix cancer patients were subjected to simultaneous multiparametric PET/MRI with [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO). Imaging was scheduled before, twice during and after chemoradiotherapy. Intra- and inter-time point analyses of the extracted parameters (i.e. ADC, K^trans, A_Brix, [¹⁸F]FMISO-tumor to background ratio (TBR)) were performed. The [¹⁸F]FMISO uptake- and ADC-spatio-temporal changes were assessed. Patient averaged ADC values increased from baseline to follow up (1.03 ± 0.11/1.30 ± 0.13 × 10^-3 mm²/s), while the TBR decreased (1.73 ± 0.24/1.36 ± 0.19), K^trans dropped over time (0.17 ± 0.05/0.05 ± 0.05 min^-1); for all above p < 0.05. None of these parameters correlated significantly on a voxel-by-voxel basis. Low-ADC regions spatially varied over time. There was pronounced reduction of the [¹⁸F]FMISO-avid volumes during treatment. The suggested hybrid PET/MRI protocol to non-invasively investigate tumor hypoxia, perfusion and microstructure at one stop was feasible, revealing spatio-temporal response patterns that could be utilized for comprehensive sub-target definition for dose painting and response assessment.