ESTRO 37 Abstract book

ESTRO 37

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mean shift towards posterior and inferior was observed (Figure 2).

procedure of these 3 analysis was the following: a number of ROIs were segmented on the first or reference CT, then all the images were exported to 3D Slicer v4.5.0 where rigid registration was performed and the ROIs were translated from the reference CT to the second. Next the images and ROIs of both CT studies were imported into IBEX v1.0 where the RFs were calculated. After selecting the most reproducible RFs based on the concordance correlation coefficient (CCC) and the coeffcient of variation (CV), an hierarchical cluster analysis was carried out to discard redundant features. A total of 177 RFs pertaining to three main categories (Intensity, Shape and Texture) were evaluated. In the Texture group in turn we calculated 3 different subgroups related to 3 calculated matrices: Neighborhood Intensity Difference Matrix, Gray Level CoOcurrence Matrix and Gray Level Run Length Matrix.

Results The result of the TEST-RETEST showed that 91% of the RFs were reproducible according to CCC. With respect to the influence of the modification of the CT acquistion parameters on the reproducibility of the RFs (intra-CT) the results ranged from 89.3% to 43.1% where the pitch factor and the reconstruction algorithm were modified respectively. Inter-CT RFs reproducibility also showed large material differences: from 85.3% (wood) to only 15.8% (polyurethane). Reproducible RFs were obtained only under changes of FOV, mAs, kVp and for the PMMA as the most water-like material. After the hierarchical cluster analysis(Image 2) 10 reproducible and non- redundant RFs were left(Kurtosis or Global Median among others)

Conclusion The present study shows that our method for automatic prostate FM detection in 4D cine MR data is robust and accurate. This dataset was acquired under conditions that are representative for hypofractionated prostate treatment and will help to develop real-time MR- guidance on an MRI linac system. PO-0989 Identification of reproducible and non redundant intra and inter CT scanner Radiomics features. R. Berenguer 1 , V. De la Vara 1 , M.D.R. Pastor-Juan 2 , M.V. Villas 1 , J. Canales-Vazquez 3 , M. Castro-Garcia 3 , S. Sabater 1 1 Hospital General de Albacete, Servicio de Radioterapia, Albacete, Spain 2 Hospital General de Albacete, Servicio de Radiologia, Albacete, Spain 3 University of Castilla-La Mancha, Renewable Energy Research Institute, Albacete, Spain Purpose or Objective Radiomics is a growing field of research but results can be influenced by image acquisition techniques. Our aim was to identify reproducible and non redundant intra and inter CT scanner Radiomics features (RFs). Material and Methods Three different analysis were carried out to evaluate reproducibility. Firstly a phantom was imaged two days apart to carry out the TEST-RETEST analysis. Secondly the same phantom was imaged changing all the CT acquisition parameters one by one in the same scanner to evaluate the reproducibility of the RFs. Finally a second phantom with 10 different materials (Image 1) was imaged by 5 different scanners with exactly the same acquisition parameters to evaluate the inter-CT reproducibility of the RFs. In brief, the common

Conclusion After evaluating the reproducibility of 177 RFs under the TEST-RETEST, intra-CT and inter-CT comparison we conclude that care must be taken since a lot of RFs must be discarded. CT image acquisition parameters influence Radiomics results, so tight acquisition protocols must be established. If all the CT parameters are fixed except FOV, mAs and kVp (which could be varied from patient to patient in clinical routine), the 10 RFs obtained should be reproducible and informative for clinical studies. Results