ESTRO 2022 - Abstract Book

S133

Abstract book

ESTRO 2022

Figure 2: Scatterplot between and D mean and Δ SUV mean . Each point denotes a vertebra and the solid line indicates the rolling mean. Conclusion This study used longitudinal FDG-PET/CT scans as a unique method to demonstrate both a dose-response of the hematopoietic activity in bone marrow as well as a patient-dependent compensatory response in non-irradiated bone marrow. These results are the first step towards an in-depth evaluation of using FDG-PET to obtain a better understanding of the bone marrow’s dose-response, compensatory response, and hematological toxicity.

PD-0158 Evaluation of ERI as response predictor in cervical cancer: a retrospective study on T2 and DWI MR

D. Cusumano 1 , R. Autorino 2 , L. Boldrini 1 , B. Gui 2 , L. Russo 2 , S. Persiani 2 , G. Panza 3 , A. Nardangeli 4 , M. Campitelli 5 , M.G. Fernandina 6 , G. Macchia 7 , V. Valentini 2 , M.A. Gambacorta 4 1 Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Rome, Italy; 2 Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Roma, Italy; 3 Università Cattolica del Sacro Cuore, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Roma, Italy; 4 Fondazione Policlinico Agostino Gemelli IRCCS, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Roma, Italy; 5 Fondazione Policlinico Agostino Gemelli IRCCS , Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Roma, Italy; 6 Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Woman, Child and Public Health Department, Roma, Italy; 7 Molise Hospital, Radioterapia, Campobasso, Italy Purpose or Objective Despite numerous experiences published in the literature, few clinical trials today use radiomics to personalize cancer treatment. This is because radiomic models generally use complex parameters and advanced techniques, that do not allow a clear interpretation of the mechanism behind the prediction: the low interpretability leads clinicians to not trust these models. As a consequence, new biomarkers are emerging that are simple to calculate and based on robust radiobiological theories: Early Regression Index (ERI), is an image-based biomarker that has recently reported interesting results in predicting pathological complete response (pCR) after neoadjuvant chemoradiotherapy (nCRT) in case of rectal cancer. Such parameter is generally calculated on T2 MR images and consists in modelling the early tumour regression combining the GTV volume measured during simulation (V pre ) and at mid therapy (V mid ). ERI=-ln(1-(Vmid/Vpre)^Vpre)) This study aims to evaluate the feasibility of using ERI in Locally Advanced Cervical Cancer (LACC), evaluating its ability in predicting pCR not only considering T2-w MR images, but also DWI Materials and Methods A total of 88 patients affected by LACC (FIGO IB2-IVA) were enrolled. All the patients underwent nCRT, combining weekly 40 mg/m 2 of cisplatin with concurrent RT, prescribing 50.6 Gy to PTV1 (CTV1+5 mm) and 39.6 Gy to PTV2 (CTV2+7mm) in 22 fractions. An MRI protocol consisting in two acquisitions (T2-w and DWI) in two times (before treatment and at mid therapy) was applied. GTV was delineated and ERI was calculated for both imaging modalities. A radical hysterectomy was performed for each patient within 8 weeks after nCRT: pCR was considered in case of absence of any residual tumour cells at any site (pR0). The ERI performance in identifying pCR patients was quantified calculating the area (AUC) under the Receiver Operating Characteristic (ROC) curve. The best threshold value was obtained maximizing the Youden Index and the values of sensitivity and specificity were calculated at this threshold. Results The ROC curves obtained for ERI calculated starting from the volumes measured on T2-w MR images (ERI_T2) and on DWI images (ERI_DWI) are reported in figure 1. The performance of ERI_DWI (AUC=0.81 with 95%CI of 0.70-0.91) are superior to those reported by ERI_T2 (AUC=0.76 with 0.65-0.87 as 95% CI). At the best cut-off threshold, ERI_T2 shows high specificity (97,4%) with low sensitivity (43%), while ERI_DWI high sensitivity (86.5%) and limited specificity (64.1%).