ESTRO 36 Abstract Book

S163 ESTRO 36 2017 _______________________________________________________________________________________________

Gambacorta 1 , R. Autorino 1 , M. Campitelli 1 , A. Testa 3 , G. Chiloiro 1 , J. Lenkowicz 1 , C. Casà 1 , G. Scambia 3 , L. Bonomo 2 , V. Valentini 1 1 Università Cattolica del Sacro Cuore -Policlinico A. Gemelli, Radiation Oncology Department , Rome, Italy 2 Università Cattolica del Sacro Cuore -Policlinico A. Gemelli, Radiology Department, Rome, Italy 3 Università Cattolica del Sacro Cuore -Policlinico A. Gemelli, Gynecology Department, Rome, Italy Purpose or Objective Standard treatment in cervical cancer (CC) is largely based on chemoradiation (CRT) for locally advanced stages. The role of surgery after a first time of CRT is limited to selected protocols. In such cases it is possible to assess the pathological complete response (PCR). A fractal is an object having geometric shape that can be divided into subparts, each of which is a reduced copy of the whole. This property, known as self-similarity, can be measured by the Fractal Dimension (FD). Aim of this study is finding an enhanced by FD radiomics signature detecting patients with PCR. Material and Methods Pathologically proven CC patients underwent to CRT after MR definition of the local stage. T2 High-Resolution images were used for delineating GTV. A home-made software was used for assessing radiomics features after pre- processing images by Laplacian of Gaussian (LoG) filter and tuning its σ parameter, and for extracting fractal dimension (FD) on raw images. FD was extracted at different threshold levels considering all deciles between 10% and 100% of signal intervals inside the GTV volume analyzed slice by slice by using the box-counting technique. Stepwise logistic regression (SLR) models were used for predicting PCR using FIGO Stage, 1 st order features (skewness, kurtosis, entropy) and different thresholds for FD. AUC of ROC and calibration, were determined for internal validation. Results 177 patients were retrospectively recruited (FIGO stage Ib – IVb). FD was the only significant predictor for the whole dataset in SLR (MaxDF@10%: P-Value<0.001, MinDF@0- 90%: P-Value<0.05, see fig. 1). AUC of ROC was 0.70 with not significant deviance at calibration. After selecting patients according to the MR pixel spacing (PS) the most numerous group was found in patients having PS=0.58mm (69 patients). A new SLR model showed significance of entropy (σ=2.36mm, P-Value<0.05), kurtosis (σ=1.23mm, P-Value<0.01) and MinDF@0-90% (P-Value<0.01), with AUC

Conclusion Acute toxicity following single dose IMRT-based preoperative APBI appears to be mild. Clinically feasible optimal and acceptable OAR constraints were developed for future studies. Long-term follow-up is required for validation and the skin dosimetry constraints, in particular, may need additional modification based on long-term outcomes. Chronic toxicity will be available at the 36 th ESTRO conference. [1] Olivotto et al. 2013 [2] van der Leij et al. 2014 OC-0317 MR radiomics and fractal dimension in cervical cancer predicting pathological complete response N. Dinapoli 1 , A.L. Valentini 2 , A. Pesce 1 , R . Gatta 1 , C. Masciocchi 1 , V. Ninivaggi 2 , B. Gui 2 , G. Matt ana 1 , M.A.