ESTRO 38 Abstract book

S796 ESTRO 38

Material and Methods Patients affected by LARC undergoing neoadjuvant chemoradiotherapy on a hybrid 0.35 T MRgRT unit were considered for this analysis. Prescribed dose was 55 Gy to primary tumor and corresponding mesorectum (PTV1) and 45 Gy to pelvic nodes and mesorectum (PTV2) delivered through a simultaneous integrated boost approach. The cCR was assessed with a MR acquired 6 weeks after chemoradiotherapy and digital examination (DE). An imaging acquisition protocol of 6 true fast imaging with steady state precession (TRUFI) MR scans per pt was performed: the first MR was acquired at first simulation (t0) and the remaining ones at fractions t5,t10,t15,t20 and t25. All the images had a spatial resolution of 1.5x1.5x1.5 mm 3 and an acquisition time of 175 sec. In order to investigate the variation of the radiomics parameters throughout the treatment, all features were normalized respect to the value obtained in simulation (t0). A total of 52 radiomics features (morphological, statistical, textural and fractal) was firstly analyzed, while 254 ratios were calculated. The Wilcoxon Mann Whitney test was performed to identify the feature whose variation can be more predictive of cCR.

Fig. 1

Conclusion Clinical trials over the KRAS oncogene status and treatment outcomes in LARC are limited, thus we focused on the potential of KRAS oncogene status as a biological predictive marker. Although KRAS status seems to have slightly better prognosis in patients treated with neoadjuvant CRT followed by curative surgery in LARC, it does not reach significant results (probably due to insufficient sample) in TRG, RFS or OS. It would be interesting to carry out prospective trials with longer follow-up examining KRAS mutation in locally advanced rectal cancer for an increased understanding. EP-1468 Radiomics versus volume reduction for rectal cancer response prediction in hybrid MR guided RT L. Boldrini 1 , D. Cusumano 1 , J. Lenkowicz 1 , G. Chiloiro 1 , C. Casà 1 , C. Masciocchi 1 , F. Cellini 2 , N. Dinapoli 2 , L. Azario 1 , S. Teodoli 2 , M.A. Gambacorta 1 , M. De Spirito 1 , V. Valentini 1 1 Università Cattolica del Sacro Cuore, Dipartimento di Diagnostica per immagini- Radioterapia Oncologica ed Ematologia, Rome, Italy ; 2 Fondazione Policlinico Universitario A. Gemelli IRCCS, Dipartimento di Diagnostica per immagini- Radioterapia Oncologica ed Ematologia, Roma, Italy Purpose or Objective Hybrid Magnetic Resonance guided Radiotherapy (MRgRT) represents an innovative therapeutic approach for locally advanced rectal cancer (LARC) patients (pts). Even if daily positioning MR imaging is characterized by low spatial resolution, its superior soft tissue contrast provides better visualization of therapy volumes and allows a direct and reliable visualization of tumor response throughout the treatment. The possibility to apply a radiomics approach to these images is however still under investigation. Aim of this study was to extract radiomics parameters and compare their performance in complete clinical response (cCR) prediction with tumor volume reduction, known imaging biomarker of response.

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