Abstract Book

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ESTRO 37

provides a suitable alternative to test-retest imaging that is easily available in clinical routine. EP-2096 Sodium-MRI at ultra-high magnetic fields for early response assessment in brain tumors S. Regnery 1,2 , N. Behl 3 , D. Paech 4 , H.P. Schlemmer 4 , M.E. Ladd 3 , A. Nagel 3,5 , S. Rieken 1,2 , J. Debus 1,2 , S. Adeberg 1,2 1 University Hospital Heidelberg, Department of Radiation Oncology, Heidelberg, Germany 2 German Cancer Research Center DKFZ, Clinical Cooperation Unit Radiation Oncology, Heidelberg, Germany 3 German Cancer Research Center DKFZ, Division of Medical Physics in Radiology, Heidelberg, Germany 4 German Cancer Research Center DKFZ, Division of Radiology, Heidelberg, Germany 5 University Hospital Erlangen, Institute of Radiology, Erlangen, Germany Purpose or Objective Radiotherapy is a cornerstone in the treatment of glioblastoma and skull-base-meningioma. At present, the response assessment is mainly based on contrast- enhanced T1- and T2-weighted MRI images acquired at 3 Tesla with its well-known limitations. The increasing utilization of ultra-high magnetic fields with enhanced signal-to-noise-ratio bears great potential to enhance biological imaging. In this context, sodium-MRI is an emerging approach for tumor characterization and response evaluation. Here we present the first results of a prospective longitudinal study employing sodium-MRI on a 7-Tesla-scanner during radiotherapy of brain tumors. Material and Methods Three glioblastoma and four meningioma patients underwent imaging on a 7T-MRI-scanner (Siemens Healthineers, Erlangen, Germany) in addition to the standard 3T-MRI-protocol before, during and after definitive treatment. High-resolution T2-TSE and T2- FLAIR-imaging was performed using a 24-channel single resonant head coil. Sodium-MR-images were acquired with a double-resonant (1H/23Na) quadrature birdcage coil using a house made density-adapted 3D radial projection pulse sequence and an iterative 3D-DLCS reconstruction algorithm. 7T- and clinical 3T-MRI-images from different time points were co-registered manually using MITK. ROIs were delineated on clinical standard imaging by an experienced radiation oncologist: regions with T1-weighted Gadolinium-contrast-enhancement (gdce) representing tumorous tissue, regions of T2-FLAIR- hyperintensity representing edema and normal- appearing-white-matter (nawm). Furthermore, response evaluation was done according to RANO-criteria. Results In all glioblastoma patients, clear changes in sodium mean signal can be observed in regions of tumorous tissue and edema (Fig. 1).

first examination right after therapy. Conversely, neither the nawm in glioblastoma patients nor the tumorous tissue and nawm in the meningioma cohort (Fig. 2) show obvious signal changes.

The stability of sodium-signals in non-infiltrative disease suggests indifference of sodium imaging towards possible radiotherapy-induced changes in unaffected white matter. Thus, the signal changes in the glioblastoma cohort might particularly reflect treatment response of high-grade tumor tissue. Conclusion Radiation of glioblastoma is accompanied by considerable changes of sodium signal within the tumor tissue and surrounding edema already early after therapy with different trends in treatment responders versus non- responders. Accordingly, sodium-MRI might yield early information about treatment response in glioblastoma and merits further investigation. EP-2097 Qantification of liver function after stereotactic body radiotherapy for liver tumors M.M. Fode * shared first authorship 1 , M. Sørensen *shared first authorship 2 , J. Petersen 3 , M. Holt 1 , M. Høyer 4 1 Aarhus University Hospital, Department of Oncology, Aarhus C, Denmark 2 Aarhus University Hospital, Department of Hepatology and Gastroenterology and Department of Nuclear Medicine and PET centre, Aarhus C, Denmark 3 Aarhus University Hospital, Department of Medical Physics, Aarhus C, Denmark 4 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus C, Denmark Purpose or Objective The hepatocyte function was measured by functional positron emission tomography (PET) with a hepatocyte- specific tracer called [ 18 F]fluoro-2-deoxy-D-galactose (FDGal) in patients treated with stereotactic body radiation therapy (SBRT) for liver tumors. Dynamic FDGal PET/CT was used to determine a radiation dose-response relationship between radiation dose and liver function and the recovery of the liver function was further quantified over time. A correlation between parametric images of metabolic liver function (kmet), derived from the dynamic PET scan, and static images of standard uptake value (SUV) of FDGal was assessed. Material and Methods The liver function was assessed in 6 patients with colorectal liver metastases (n = 5) or intrahepatic colangiocarcinoma (n =1) without parencymal liver disease by FDGal PET/CT at baseline, one and three months after SBRT with total dose of 45-60 Gy delivered in 3-6 fractions. The change in FDGal metabolism as function of radiation dose was assessed by comparing doses from the treatment plan with changes in Kmet and SUV of FDGal assessed one month after SBRT. The recovery of the liver function was investigated three month after SBRT. Results After normalization of data, a clear dose-response relationship was revealed with a polynomial fit at one

Furthermore, there is a tendency towards decreasing sodium values in tumorous tissue and edema in therapy responders, whereas the opposite is true for the non- responder. This tendency already becomes obvious in the