ESTRO 36 Abstract Book

S909 ESTRO 36 2017 _______________________________________________________________________________________________

using PET-tracers such as 18 F-FMISO. Moreover, parameters derived from functional MRI have been correlated with response to RT, such as ADC. Our hypothesis is that multiparametric PET/MRI, i.e. a combination of different parameters derived from PET and functional MRI, allows a better prediction in terms of RT response than single parameters do. The aim of this study was to distinguish two different HNSCC cell-lines grown as xenografts in mice, based on voxel-wise image analysis of simultaneously acquired FMISO-PET and ADC data. Material and Methods 11 immunodeficient nude mice were injected into the hind leg with tumor-cells of human HNSCC cell-lines FaDu (n=7) or CAL-33 (n=4). Once a tumor reached its target size (~300 mm³), simultaneous PET and MR imaging was performed on a 7T-PET/MR scanner (Bruker) at two time points: before (d0) and after two weeks (d14) of fractionated irradiation (10x 2Gy). The protocol included dynamic FMISO-PET (90min), anatomical T2- and diffusion- weighted MRI. An image of the FMISO uptake was reconstructed from the last 5 min of the acquired PET data. An ADC map was calculated from a set of 9 diffusion-weighted MR images (b=0-800 s⁄mm²). On the anatomical MR image, tumor and muscle were defined as regions of interest (ROIs). ROIs and ADC map were then resampled to the PET image grid for consistent image analysis on the voxel level. FMISO tumor- to-muscle-ratios (TMRs) were determined at both time points for ROI-based and voxel-by-voxel comparison with ADC values. Results The median (d0/d14) TMRmean was 1.43/1.06 and 1.25/1.00, median ADCmean was 780/929 and 1095/1286 x10 ⁻ ⁶ mm²/s, median FMISO TMRmax was 2.55/1.57 and 1.80/1.52, median slope m of a regression line through voxelbased FMISO TMR and ADC scatter data was -2.29/- 1.25 and 0.02/-0.26 x10 ⁻ ⁴ , median ADCmean of a thresholded subregion of the tumor where FMISO TMR≥1.4 was 730 (d0) and 1145 (d0) x10 ⁻ ⁶ mm²/s for FaDu and CAL- 33 tumor ROIs, respectively. Parameter values for all tumors are presented in Fig1; a scatter plot of voxelbased FMISO TMR and ADC values for one FaDu and one CAL-33 tumor at d0, in Fig2. Out of five parameters, three had strong potential for differentiation of the HNSCC cell-line, when measured at d0: TMRmax, slope m of the regression line and ADCmean of the FMISO positive region (TMR≥1.4). Conclusion Voxelbased analysis of FMISO-PET and ADC data proved to have high potential for discrimination of tumor cell-lines presenting different radiobiological properties. Three parameters were found to be suitable to distinguish the two cell-lines with well-known difference in radiosensitivity before the start of RT. Additional sets of imaged-derived parameters will be investigated and further cell-lines be measured to identify relations with radiosensitivity for the development of a multiparametric prediction model for personalized RT in HNSCC.

EP-1689 Gleason driven dose painting based on ADC MR imaging E. Grönlund 1 , S. Johansson 2 , T. Nyholm 1 , A. Ahnesjö 1 1 Uppsala University, Medical radiation sciences, Uppsala, Sweden 2 Uppsala University, Experimental and clinical oncology, Uppsala, Sweden Purpose or Objective To investigate a Gleason driven dose painting approach for high risk prostate cancer patients based on outcome for conventional treatments, and using apparent diffusion coefficient (ADC) MR images for dose prescription. Material and Methods