Subproject 5: Early predictors for outcome based on early MRI data
Currently a weekly magnetic resonance imaging (MRI) of patients suffering from non-small-cell lung carcinoma (NSCLC) under radiotherapy (RT) is lacking. The primary objective utilizing the increased soft-tissue contrast of MRI would be a weekly response assessment of RT in terms of visualizing the actual tumor morphology including its separation from adjacent atelectasis and precise localization of neighboring organs at risk. Morphological biomarkers for prognostic response assessment could be defined by functional MRI allowing for early risk stratification of the applied RT including the daily irradiation planning or even provides the basis for the so-called dose paining concept: prescribing heterogeneous doses in the tumor volume, e.g. higher doses in malignant sub-regions and less dose where the tumor is less malignant.
In this subproject S5 the prognostic value of thoracic diffusion-weighted (DW) MRI of patients with NSCLC is assessed. DW imaging is a contrast agent free, functional imaging by monitoring diffusion of water molecules in tissue. High signal intensity provided by DW imaging and the associated low apparent diffusion coefficient (ADC) occurs in many malignant tumors. An increase in the ADC unter RT could be a surrogate for decreasing cell density in the tumor volume and hence indicates successful response to RT. The ADC maps of the very first weekly MRI under RT were characterized whether they could act as morphological biomarker for prognostic response assessment. Malignant sub-regions in the tumor volume defined by very low ADC values could be identified for future dose painting concept. Morphological discrepancies of the target volume defined by DW imaging with respect to T1- and T2-weighted sequences were assessed (Figure 1). A focus is set on the cone beam computer tomography guided radiotherapy by the ETHOS system with offline MRI image guidance.
Figure 1. Exemplary magnetic resonance imaging of a non-small cell lung cancer under radiotherapy (RT) by ETHOS machine. The axial diameter (indicated by the arrows) of the tumor is slightly declining within approx. 1 month of RT and the mean calculated apparent diffusion-weighted coefficient (ADC) in a region of interest (dotted disc) of a representative slice is increasing which could be interpreted as successful response to RT. Morphological discrepancies between T2, Dixon and diffusion-weighted imaging (DWI) and the calculated ADC map are depicted.
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