ESTRO 2024 - Abstract Book

S5072

Physics - Radiomics, functional and biological imaging and outcome prediction

ESTRO 2024

Non-Gaussian Intra Voxel Incoherent Motion Imaging (NG-IVIM) DWI model, which describes the real extracellular diffusion ( D ), as well as the intracellular diffusion ( K ), perfusion fraction (f), and pseudo-diffusion coefficient ( D* ). We described the first application of an NG-IVIM model optimized for head-and-neck [1] in a group of oropharyngeal squamous cell carcinoma (OPSCC) patients [2]. Currently, we are interested in response prediction and the added value of NG-IVIM DWI compared to ADC DWI for response prediction. With respect to the ADC DWI model, prior studies showed a low pretreatment ADC was associated with a more favourable response to (chemo-)radiotherapy [ e.g. 3-4]. However, low ADC has also been associated with HPV positive tumors [ e.g . 4-5]. Therefore, from these prior studies it is not clear if a low ADC is independently related to response, or merely a surrogate for HPV status. The aim of the current study was to determine whether conventional ADC DWI and NG-IVIM DWI parameters are surrogates for treatment response and to assess whether NG-IVIM has an added value compared to conventional ADC DWI for response prediction. To avoid the confounding effect of HPV status, we solely included HPV negative patients in this study.

Material/Methods:

Eighteen patients were prospectively included (IRB protocols 20-0207 and 21-0847). Pre-treatment MRI contained fifteen b-value DWI. The GTV was delineated by an experienced radiation oncologist on the T2w images with additional information of the gadolinium enhanced T1w images and checked on the DWI b=0 s/mm 2 images. If the shape of the pharynx deviated between the T2w and the b=0 s/mm 2 scan, the voxels from the GTV located in air on the b=0 s/mm 2 scan were excluded. The ADC and NG-IVIM parameters were calculated within the GTV. Presence of complete response ( i.e. absence of local or regional disease or distant metastasis) was scored within one year. The mean pre treatment ADC and NG-IVIM parameters in the gross tumor volume were compared between patients with and without complete response, using a Wilcoxon rank sum test. No correction for multiple testing was preformed due to the small sample size.

Results:

A significantly lower NG-IVIM diffusion coefficient D was found for patients with progressive disease compared to complete responders, but no relation with ADC (Figure 1) or other NG-IVIM parameters was observed in the HPV negative cohort.