ESTRO 37 Abstract book

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ESTRO 37

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.

month after SBRT. The dose-response semeed two-phasic. A linear decline in hepatocyte function was observed with doses below 30 Gy. At higher doses the decline seemed less pronounced. A 50% reduction in liver function was quantified at 17.8 Gy (CI 95%: 12.0-25.8) delivered in three fractions. The mean recovery rate was highest in the volumes of liver receiving doses below 20 Gy. A linear correlation was observed between Kmet and SUV of volumes receiving varying doses. Conclusion A radiation dose dependent decrease in liver function was observed in patients treated with SBRT for liver tumors one month after treatment. Recovery of liver function was observed with radiation dose below 20 Gy. The dose- response relationship was the same for parametric images of Kmet and SUV. EP-2098 Bioluminescence tomography-guided radiation therapy for GBM in vivo Z. Deng 1 , X. Xu 1 , Z. Belcaid 2 , T. Garzon-Muvdi 2 , A. Luksik 2 , R. Maxwell 2 , I. Iordachita 3 , J. Yu 4 , M. Lim 2 , J.W. Wong 1 , K.K.H. Wang 1 1 Johns Hopkins University School of Medicine, Department of Radiation Oncology and Molecular Radiation Sciences, Baltimore- MD, USA 2 Johns Hopkins University School of Medicine, Department of Neurosurgery, Baltimore- MD, USA 3 Johns Hopkins University, Laboratory for Computational Sensing and Robotics, Baltimore- MD, USA 4 Shaanxi Normal University, School of Physics and Information Technology, Shanxi, China Purpose or Objective Current treatment outcome for GBM is dismal. Preclinical study is needed to develop new radiation therapy(RT) options. CBCT-guided small animal radiation research platform(SARRP) has gained its popularity. However, CBCT is limited in guiding RT for GBM because of low imaging contrast. Alternatively, we developed bioluminescence tomography(BLT) to guide SARRP irradiation. The BLT can accurately reconstruct the center of mass(CoM) of the GBM model. We further utilized contrast-enhanced CBCT to delineate GBM volume. The relationship between the GBM volume and time of growth provides an estimated irradiation volume to be used in BLT-guided RT. In this study, we will validate the BLT-guided RT and devise the margin and beam collimation based on the BLT-reconstructed CoM and the estimated tumor volume. Material and Methods Our BLT system consists of an optical assembly, a mobile cart and a moveable mouse bed. SARRP CBCT image is acquired for planning and to generate anatomic mesh for BLT reconstruction. To establish GBM model, GL261-Luc cells were injected into left striatum. Mice were subject to multispectral bioluminescence imaging, followed by SARRP CBCT and BLT reconstruction, 1-4 weeks after the implantation. Contrast-enhanced CBCT imaging was used to delineate GBM and to verify the localization accuracy of the BLT system. To reduce the uncertainty of BLT reconstruction, we will apply differential evolution algorithm to optimize the optical properties of mouse brain by minimizing the distance between the CoMs of BLT and contrast imaging. The residual uncertainty will be included in the margin for irradiation. The volume of contrast-labeled GBM vs. time of growth will be established to provide the irradiation volume. For the 1- week time point, it is still challenging to reveal the GBM volume with the contrast imaging. MRI will be used to assist the tumor delineation. Equivalent sphere of the average tumor volume at different time points of tumor growth will be used to design beam collimation. For irradiation, we will localize the GBM with BLT reconstructed CoM and apply the estimated volume and margin to collimate the radiation beam. H&E and γH2AX

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