ESTRO 2021 Abstract Book

S1220

ESTRO 2021

Results The complete closure of the fistula was achieved in 100% (43/43) of the patients. Three patients required re- irradiation due to persistence. Three patients showed partial response needing reirradiation, with the same treatment plan, and also achieved complete response. The average time between surgery and RT was 38 days with a range between 7 and 110 days. The average duration of treatment was 5 consecutive days (range 2-7 days). 90.7% (39) of the patients were treated with a dose of 7.5 Gy in 5 daily sessions (1.5 Gy / session). Other dose fractionations used were: 5.5 Gy in 3 fractions in 1 patient (1.5 Gy + 1.5 Gy + 2.5 Gy), 8 Gy to 4 Gy / fraction in 2 patients and 15 Gy to 3 Gy / fraction in 1 patient. No related acute or late side effects were observed with the treatment. Conclusion Our retrospective analysis shows that an irradiation dose of 7.5 Gy with small fractions such as 1.5 Gy can completely solve lymphatic fistulas in most patients. RT in these situations has a good safety profile. Therefore, RT is a solid, effective, safe and economic treatment option for the persistent lymphorrheas. 1 Heidelberg University Hospital, Department of Radiation Oncology, Heidelberg, Germany; 2 National Center for Tumor diseases, (NCT), Heidelberg, Germany; 3 Heidelberg Institute of Radiation Oncology , (HIRO), Heidelberg, Germany; 4 Heidelberg University Hospital, Department of Nuclear Medicine, Heidelberg, Germany; 5 Heidelberg Institute of Radiation Oncology, (HIRO), Heidelberg, Germany; 6 Heidelberg University Hospital, Department of Radiation Oncology , Heidelberg, Germany; 7 National Center for Tumor diseases, (NCT) , Heidelberg, Germany; 8 Heidelberg Institute of Radiation Oncology, (HIRO) , Heidelberg, Germany; 9 Heidelberg Ion-Beam Therapy Center (HIT), Department of Radiation Oncology, Heidelberg, Germany; 10 Clinical Cooperation Unit Nuclear Medicine, German Cancer Research Center (DKFZ), Heidelberg, Germany; 11 Translational Lung Research Center Heidelberg (TLRC), German Center for Lung Research (DZL), Heidelberg, Germany; 12 Clinical Cooperation Unit Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 13 German Cancer Consortium (DKTK), partner site Heidelberg, partner site Heidelberg, Heidelberg, Germany; 14 German Cancer Consortium (DKTK), partner site Heidelberg, Heidelberg, Germany; 15 Department of Nuclear Medicine, University Hospital Duesseldorf, Duesseldorf, Germany Purpose or Objective For local therapies like radiotherapy reliable staging tools are essential. 68 Ga-FAPI (fibroblast activation protein inhibitor) is a rapidly evolving and highly promising radiotracer for PET/CT imaging showing excellent results in a variety of tumor entities. This retrospective study aimed to evaluate the potential of FAPI-PET/CT in rare diseases based on biodistribution and tumor uptake and thus facilitate therapeutic approaches such as (radio-)oncological management. Materials and Methods 55 patients with rare tumor entities defined by an incidence of 1 person out of 2000 or less underwent 68 Ga- FAPI-PET/CT. We included 14 women and 41 men (median age: 60 years) within the following subgroups: cancer of unknown primary (n=10), head-and-neck-cancer (n=13), gastrointestinal and biliary-pancreatic cancer (n=17), urinary tract cancer (n=4), neuroendocrine cancer (n=4) and others (n=7). Tracer uptake was quantified by standardized uptake values (SUV)max and (SUV)mean and the tumor-to-background ratio (TBR) was determined. Moreover, the impact of 68 Ga-FAPI-PET/CT on (radio-)oncological management was evaluated. Results 68 Ga-FAPI-PET/CT identified the primary tumor in 20 out of 55 patients and 31 patients with metastases (n=88) demonstrating a high mean SUVmax (primary tumors: 10.1; metastatic lesions: 7.6). Highest uptake was obtained by liver metastases with a mean SUVmax of 9.8 and a rather high TBR of 8.7, tightly followed by peritoneal carcinomatosis presenting a mean SUVmax of 9.8 and an excellent TBR of 29.6. In terms of the included subgroups the highest uptake regarding mean SUVmax was observed in gastrointestinal and biliary- pancreatic cancer with 9.8 followed closely by urinary tract cancer with 9.5 and head-and-neck cancer (9.1). 68 Ga-FAPI-PET/CT enabled early treatment response evaluation and improved radiotherapy planning leading to a high impact on (radio-)oncological management. PO-1490 The impact of 68Ga-FAPI-PET/CT on (radio-)oncological management for rare diseases S.A. Koerber 1,2,3 , K. Dendl 4 , R. Finck 4 , C. Kratochwil 4 , J. Ristau 1,2,5 , S. Adeberg 6,7,8 , H. Rathke 4 , M. Röhrich 4 , T. Lindner 4 , K. Herfarth 1,7,8,9 , U. Haberkorn 4,10,11 , J. Debus 1,2,5,9,12,13 , F.L. Giesel 4,10,14,15