Abstract Book

S1164

ESTRO 37

better results in the assessment or response than RECIST 1.1. Central liver metastases were associated to greater biliary dilation than peripheral lesions: contingency analysis indicated that the absence of biliary dilatation was more frequent in peripheral lesions than in central lesions (P=1.0x10-5). However, there was no difference between the frequency of patients who had preexisting dilation and the frequency of patients who developed it during treatment, whether the lesion was central (P = 0.330) or peripheral (P=0.522), so no significant differences were observed between SBRT and other treatments/conditions. Finally, transitory decrease in liver attenuation surrounding lesions was observed at first trimester after SBRT, when the attenuation coefficient values were lower than in any of the other revisions including baseline measurement (P<0.016) with no other significant changes during the first year of follow-up. Conclusion RECIST 1.1, the most commonly employed criteria to assess response to SBRT of liver metastases, is not the most accurate criteria for this evaluation, being more suitable CHOI criteria, and above all, PERCIST. EP-2117 Effect of Interpolation on 3D Texture Analysis of PET Imaging in Oesophageal Cancer P. Whybra 1 , K. Foley 2 , C. Parkinson 1 , J. Staffurth 3 , E. Spezi 1 1 Cardiff University, School of Engineering, Cardiff, United Kingdom 2 Cardiff University, Division of Cancer & Genetics, Cardiff, United Kingdom 3 Cardiff University, School of Medicine, Cardiff, United Kingdom Purpose or Objective Radiomics supposes that medical images can be used as quantitative, mineable data for improved tumour profiling and personalised treatment planning [1]. Three- dimensional texture analysis (TA), a subset of radiomics, is thought to reveal an abundance of quantitative information not characterised by slice-by-slice, 2D TA. Most scan reconstruction in PET/CT produce anisotropic voxel dimensions. For 3D TA, an isotropic voxel size is advised to ensure no directional bias and is achieved via interpolation. To the best of our knowledge, the optimal voxel size and approach to interpolation is not yet standardised. We explore the effect of interpolated voxel size on selected TA features for an oesophageal cancer (OC) dataset. Material and Methods A cohort of 374 biopsy-proven OC patients were included, all radiologically staged with the same scanning protocol. The feature extraction algorithms were developed in- house and validated as part of an international initiative [2]. Results were obtained from the original voxel dimension, ‘Orig’ (0.2734, 0.2734, 0.3270) mm 3 and interpolated voxel dimensions (15mm 3 , 18mm 3 , 20mm 3 , 22mm 3 , 25mm 3 ). Tumours were discretised with a fixed bin width of 0.5 SUV prior to TA. For each feature, patients were assigned a rank based on the result for the original voxel dimension (1 for lowest value). This rank was then used for a consistent comparison with 5 different linearly interpolated voxel sizes. Results Due to the quantity of metrics, we focus this report on GLCM features which have been recently shown to be repeatable [3]. Figure 1 displays the effect of interpolation on feature value and rank for selected GLCM features. We see that dissimilarity, difference entropy and correlation show systematic change and variation in rank depending on voxel dimension, whereas sum entropy does not. For the three features showing variation with interpolation there is a clear pattern of

EP-2116 Recist Vs Choi Vs Percist In Evaluating Response To Sbrt Of Liver Metastases. M. Allona Krauel 1 , O. Hernando Requejo 2 , E. Sanchez Saugar 2 , U. Lopez De La Guardia 1 , C. Rubio Rodríguez 2 1 hospital Hm Sanchinarro, Radiology, Madrid, Spain 2 hospital Hm Sanchinarro, Radiation Oncology, Madrid, Spain Purpose or Objective To describe imaging characteristics of liver metastases treated with Stereotactic Body Radiation Therapy (SBRT) and to compare the accuracy (reliability and precociousness) of different imaging criteria (RECIST 1.1, Choi and PERCIST) in assessing response to treatment. Material and Methods We selected 88 liver metastases treated with SBRT and Gating technique (45-60 Gy in 3 to 5 fractions) at our institution between april 2008 and November 2014. All the lesions presented clinical and radiological local control one year after SBRT treatment. For this retrospective study we reviewed the images of all CT and PET-CT studies performed every three months during the first year after SBRT treatment. For each of the 88 lesions (totally 373 imaging studies), we measured the size and the density and, if PET was permormed, we also analyzed the 18F-FDG uptake of the lesions, to assess response according to the different criteria (RECIST, Choi and PERCIST). We also collected data concerning surrounding liver tissue attenuation coefficient and caliber of the biliary ducts, to find if there were changes in the perilesional parenchyma and if there was a relationship between the location of the liver metastases and the appearance of biliary dilation after SBRT, respectively. We used SPSS - Statistical Package for the Social Sciences - 21.0 (SPSS Inc., Chicago, EEUU) - to collect and analyze all data. Results Statistical analysis shown significant differences in the assessment of response of liver metastases treated with SBRT between the different criteria. In the four reviews, the different scales classified the response to treatment differently (P <8x10-4). PERCIST criteria were the most accurate to assess response, detecting also this response earlier than the others. Regarding morphologic criteria, Choi criteria shown