ESTRO 37 Abstract book

S1156

ESTRO 37

EP-2099 Predicting tumour response to chemoradiotherapy in rectal cancer using dynamic contrast enhanced MRI K.M. Bakke 1 , S. Meltzer 1 , L.G. Lyckander 2 , S.H. Holmedal 3 , A. Negård 3 , K.I. Gjesdal 3 , E. Grøvik 4 , K.R. Redalen 5 1 Akershus University Hospital, Department of Oncology, Oslo, Norway 2 Akershus University Hospital, Department of Pathology, Oslo, Norway 3 Akershus University Hospital, Department of Radiology, Oslo, Norway 4 Oslo University Hospital, Department of Diagnostic Physics, Oslo, Norway 5 Norwegian University of Science and Technology, Department of Physics, Trondheim, Norway Purpose or Objective To investigate whether baseline dynamic contrast enhanced (DCE)-MRI can predict tumour regression grade (TRG) in rectal cancer patients receiving chemoradio- therapy (CRT) before surgery. This could help stratifying patients into separate treatment regimens before commencement of therapy. Material and Methods Thirty-five patients diagnosed with rectal cancer underwent DCE-MRI (T1-weighted EPI, TR = 39 ms, time resolution = 1.89 s) before pre-CRT and surgery. The images were acquired as part of a multi-echo sequence (TE = 4.6, 13.7, 22.8 ms), where the T1-weighted signal was extrapolated back to magnetization at TE = 0, to exclude T2 relaxation effects. Tumour contours were drawn by two radiologists on T2-weighted axial images. We used the extended Tofts kinetic model with a population based arterial input function, as well as non- parametric approaches for image analysis of the dynamic data, and extracted median values from the whole tumour volume. Area under curve (AUC) was determined from bolus arrival up to 90 s of scan time. Patients were divided into good responders (22 patients, TRG = 1) and poor responders (13 patients, TRG = 2-3). We used t-test and receiver operating characteristics (ROC)-curve for statistical analysis. Results K trans and AUC, both parameters reflecting a combination of blood flow and vascular permeability, were significantly different between the two groups (p-value < 0.05 and < 0.01 respectively, for both radiologists), with lower values indicating favourable response. ROC-curve analysis showed a sensitivity and specificity of 73 % and 61 % for K trans (p-value = 0.04) and 91 % and 61 % for AUC (p-value = 0.01). Both parameters were normally distributed with no outliers. Conclusion We show that parameters derived from DCE-MRI can be used to predict TRG already at time of diagnosis. The AUC parameter was slightly better than K trans at predicting poor tumour response. Since AUC is more easily obtained than K trans which requires more modelling and an arterial input function, it can be more easily automated in a clinical setting. EP-2100 Development of a filter-based method for multicenter PET image harmonization in radiomic studies S. Reuzé 1,2,3 , F. Orlhac 4 , M. Ricard 5 , D. Vallot 6 , W. Ksouri 7 , A. Laprie 8,9 , L. Dercle 10,11 , E. Deutsch 2,3,12 , C. Robert 1,2,3 1 Gustave Roussy, Radiotherapy Department- Medical Physics Unit, Villejuif, France 2 Paris-Saclay University, Faculty of Medicine, Le Kremlin- Bicêtre, France 3 INSERM U1030, Molecular Radiotherapy, Villejuif, France 4 CEA-SHFJ, IMIV, Orsay, France 5 Gustave Roussy, Nuclear Medicine Department- Medical

staining will be used to validate the coverage of irradiation. Results Fig 1 shows a case of the BLT reconstruction. The 3D rendering (Fig 1d) shows 0.6mm difference between the CoMs of the contrast-enhanced and BLT volume.

We further studied if the BLT localization accuracy depends on tumor size by assessing the CoM location for a GBM that has grown 1-4 weeks (Fig 2, tumor size:12– 113mm 3 ). We found the average BLT CoM is within 1.3mm with that of contrast-enhanced volume and no volume dependence was found. The efficacy of using such margin for irradiation is being validated.

Conclusion Our results demonstrate the BLT-SARRP can be a novel system to guide radiation in vivo. By utilizing the BLT reconstructed CoM and the contrast-labeled GBM volume, we expect to provide optimal margin and collimation to deliver conformal irradiation for GBM model.