ESTRO 2021 Abstract Book

S1659

ESTRO 2021

delineated on pre-PET images and duplicated on post-PET images, matched by a deformable registration. Linear correlation between pre/post uptakes values were used to determine a cumulative chart with linear trend of each patients. Results 2D Voxel maps allows to determine a graphic outcome from SUV assessment. All voxel maps were in line with Radiation Oncologist’s outcome evaluations. Collecting all results from voxel maps on a cumulative trend chart, linear trend of A,B,D and E cases was showing the same result of PERCIST evaluation (CMR,CMR,PMR,SMD). Only linear trend in case C was suspected because different (CMR) from PERCIST evaluation (PMR).

Conclusion Our preliminary study shows that RTTs could perform a quick and easy evaluation in order to support radiation oncologist in a new follow-up workflow. Future prospective of this study will investigate basic skills needed to perform the voxel analysis, effectiveness of deformable registration for this process and robustness or bias from the approved PERCIST assessment to this easy supported workflow. PO-1948 comparison between the use of PET-CT and high-field MRI 3.0T in adenoid cystic carcinoma L. Anemoni 1 , A. Mancin 1 , L. Preda 2 , M.S. Cadeo 1 , I.E. Mascayano 1 , S. Tampellini 1 , E. Orlandi 1 1 Fondazione CNAO, Radiotherapy, Pavia, Italy; 2 IRCCS Policlinico san Matteo, Radiology, Pavia, Italy Purpose or Objective Positron emission tomography (PET-CT) 11C-methionine (MET PET-CT), in combination with traditional imaging are used in hadrontherapy both in the planning phase and follow-up. The main goal of this retrospective study is the assessment of the correlation between the treatment volumes, defined with MET PET-CT, and the potential clinical impact of any discrepancies. The secondary objective is to assess the sensitivity, specificity, the positive and negative predictive value of the multi-methodological approach of high-field Magnetic Resonance Imaging (MRI) in the assessment of early response to the therapy. With this study we also estimated the degree of concordance with PET-CT method and with the only morphological MRI. It was analysed the images obtained by PET-CT and MRI of 25 patients suffering adenoid cystic carcinoma (ACC) treated at CNAO from 2012 to 2019 with hadrontherapy. Based on histology, we define Gross Tumor Volume (GTV) on MET PET-CT and also on MRI images (GTV 3T ) by using a multi-methodological approach (imaging, diffusion, perfusion and spectroscopy) of high-field MRI (3.0 T). The variables of the study were expressed as a volume (cm3). The clinical evaluation, confirming the effective response to the treatment will be performed through routine follow-up examinations after the end of radiotherapy treatment Materials and Methods

A GTVrifPET and a GTV were defined, evaluated on MRI (GTV 3T ) images using a multi-methodological approach of high-field MRI (3.0 T). Clinical Target Volume (CTV) was also analysed in relation to GTV. The variation of these volumes was analyzed in a descriptive way according to the definition of volume and percentage changes. In the assessment of GTV 3T , the following sequence was taken into account: -head-neck district, Turbo-Spin-Echo T2w sequence (matrix 512) in the axial plane of space At the end of the treatment, patient underwent clinical and instrumental examinations according to internal PDTA and national/international guidelines. MRI was performed using multichannel phased-array coils, according to tumor location