ESTRO 2020 Abstract book

S165 ESTRO 2020

Poster discussion: PH: Quantitative functional and biological imaging

Conclusion For patients with lower gastrointestinal malignancies, FAPI-PET/CT was able to demonstrate very promising results with regard to uptake and restaging. Given its short uptake time and the absence of requirements for the patient to fast prior to the study, 68 Ga-FAPI-PET/CT could be ideal for (radio)oncological management and may open up new applications for individualizing treatments not only for patients with tumors of the lower GI-tract. PD-0297 Estimating the probability of active tumor in cervical cancer derived from PET/MR-imaging L. Kravic 1 , H.E.S. Pettersen 1 , L.B. Hysing 1,2 , M. Daniel 3 , D. Georg 3 , E.M. Høye 1 , C. Ekanger 1 , D. Thorwarth 4 , S.M.C. Pilskog 1,2 1 Haukeland University Hospital, Department of Oncology and Medical Physics, Bergen, Norway ; 2 University of Bergen, Faculty of Mathematics and Natural Sciences, Bergen, Norway ; 3 Medical University of Vienna/AKH Vienna, Department of Radiation Oncology, Vienna, Austria ; 4 Eberhard Karls University Tübingen, Section for Biomedical Physics- Department of Radiation Oncology, Tübingen, Germany Purpose or Objective The aim of this study was to implement a multivariate logit model to derive the probability distribution of active cancer (PAC) in cervical cancer and to evaluate to which extent the PAC is affected by the different imaging parameters. Material and Methods Nine patients with locally advanced cervical cancer who underwent simultaneous multiparametric imaging (diffusion weighted MR, contrast enhanced MR and [ 18 F]FMISO PET) performed on a hybrid MR/PET (mp- MR/PET) scanner were analysed. Parameters (ADC, K trans and normalized PET-uptake values) derived from the mp- MR/PET images were analysed with a logit model to assess the PAC within the delineated GTV. To calibrate the logit model we reviewed literature for studies using mp-MR/PET parameters to discriminate between tumor and normal cervical tissue. From these studies we extracted classification cutoff values verified by pathology with their corresponding sensitivity and specificity as well as general details on the imaging- and patient data. For each patient, the voxelwise probability of active cancer (PAC) was calculated for the mp images utilizing the MICE Toolkit software with the multivariate logit model. Reviewed parameter thresholds (Table) and the reported sensitivity were used as weights to convert image intensity to PAC. PAC was derived for the GTV, on both the individual parameters and from a combination of all imaging parameters. Peaks in the histogram of the PAC distribution and the spatial distribution of PAC were compared for the nine patients. Results More than 145 papers with relevant input data for mp- PET/MR were reviewed (Table).

PD-0296 FAPI-PET/CT as a novel diagnostic imaging probe – first clinical experience in radiation oncology S. Koerber 1 , J. Ristau 1 , F. Staudinger 2 , C. Kratochwil 2 , S. Adeberg 1 , M.F. Haefner 1 , M. Syed 1 , H. Rathke 2 , E. Winter 2 , T. Lindner 2 , K. Herfarth 1 , U. Haberkorn 2 , J. Debus 1 , F.L. Giesel 2 1 Heidelberg University Hospital, Department of Radiation Oncology, Heidelberg, Germany ; 2 Heidelberg University Hospital, Department of Nuclear Medicine, Heidelberg, Germany Purpose or Objective Reliable imaging methods are essential for radiotherapy planning and target volume delineation. In this setting, FDG-PET has been partially disappointing due to physiological uptake in normal bowel and unspecific uptake in inflammatory tissue. Recent development of quinoline-based ligands targeting cancer-associated fibroblasts demonstrated promising preclinical and clinical results [1,2]. Therefore, the current study reports the first clinical experience with 68Ga-fibroblast-activation- protein inhibitors (FAPI)-PET/CT with regard to (re- )staging and (radio)oncological management. Material and Methods We performed 68 Ga-FAPI-PET/CT for 22 patients with primary malignancies of the lower GI-tract on an individual-patient basis. The cohort included 15 patients with metastatic disease, 1 patient with suspected local relapse and 6 treatment-naïve patients. Tracer uptake was quantified by standardized uptake values (SUV)max and (SUV)mean. After comparison with standard imaging, changes in tumor stage and (radio)oncological management were recorded. Results After FAPI-imaging, a high tumor-to-background ratio of more than 3 in most lesions was observed due to a low background activity in normal tissue. The highest uptake of FAPI tracer was found in liver metastases and anal cancer with a SUVmax of 9.1 and 13.9, respectively. In treatment-naïve patients, TNM was changed in 50% while for patients with metastases a change of tumor stage as well as size and localization of metastases occurred in 47%. In total, FAPI-imaging caused a change of (radio)oncological management in 67%. For almost every patient undergoing irradiation, target volume delineation was improved by FAPI-PET/CT.