ESTRO 36 Abstract Book

S52 ESTRO 36 _______________________________________________________________________________________________

5. Zegers CM et al. In-vivo quantification of hypoxic and metabolic status of NSCLC tumors using [18F]HX4 and [18F]FDG PET/CT imaging. Clin Cancer Res 2014. 20(24):6389-97. SP-0104 The impact of tumour heterogeneity on radiation therapy outcomes M. Gerlinger 1 1 The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom Intratumour heterogeneity, characterized by branched evolution with multiple subclones that evolve simultaneously, has been identified in most solid tumour types. Subclones may vary in their therapy sensitivity and are often spatially segregated. The talk will discuss how this subclonal heterogeneity complicates effective targeting and the potential role of combination therapy approaches and focal therapies as key strategies to address heterogeneity. OC-0105 Hybrid F-MISO PET/MRI for radiation therapy response assessment in cervix cancer M. Daniel 1,2 , P. Andrzejewski 1,2 , A. Sturdza 2 , K. M ajercakova 1,2 , P. Baltzer 1,3 , K. Pinker 1,2 , W. Wadsak 1,4 , R. Pötter 1,2 , T. Hellbich 1,3 , P. Georg 1,5 , D. Georg 1,2 1 Medical University of Vienna, Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria 2 Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria 3 Medical University of Vienna, Department of Biomedical Imaging and Image-guided Therapy, Vienna, Austria 4 Medical University of Vienna, Department of Nuclear Medicine, Vienna, Austria 5 EBG Med Austron GmBH- Wr. Neustadt, Wr. Neustadt, Austria Purpose or Objective To investigate the spatio-temporal stability of the tumor characteristics in cervix cancer patients undergoing radiotherapy with advanced imaging methods. More specifically, repetitive multiparametric MR-PET imaging prior, during and after the end of chemo- radiotherapy was performed utilizing a hybrid scanner. Material and Methods Six patients with cervical cancer participated in this prospective study. All patients received chemo- radiotherapy, with a total IMRT prescription dose of 45Gy (25x1.8Gy in 5days/week) followed by a MRI guided brachytherapy boost (4x7Gy). Patients underwent four PET/MR examinations performed on a Siemens Biograph mMR PET/MR at baseline (BL), in treatment week 2 (TP1) and 4 (TP2) of the IMRT schedule, and 3 months after end of treatment (FU). At all time-points T2w turbo spin echo, DWI, DCE T1w gradient echo with 35 repetitions and hypoxia PET scans with 18F-fluoromisonidazole (F-MISO) were acquired. ADC, K trans and iAUC maps were generated (cf. figure).

iAUC), diffusivity (ADC) and F-MISO-avidity (TBR). The TBR was evaluated for the mean of the peak-sphere and the top 10% (TBR top10% ) and the mean (TBR mean ) of the TBR values in the whole GTV. Paired t-tests were performed to evaluate statistical significance. Results The mean volume of the GTV decreased from 62±42cm 3 (BL) to 50±35cm 3 (TP1) and 20±18cm 3 (TP2). The cervix volume at FU was 24±4cm 3 . The mean GTV ADCs (in x10 - 3 mm 2 /s) were 0.98±0.10 at BL, and significantly increased during follow up investigations with 1.17±0.15 at TP1, 1.16±0.10 at TP2 and 1.25±0.12 at FU. No significant changes were found for the TBR peak . However, for the TBR mean as well as the TBR top10% the following drop was observed: from 1.81±0.14 (BL) to 1.52±0.10 (TP2) and 3.24±0.40 (TP1) to 2.40±0.39 (TP2), respectively. Intensity of T2w images, K trans and iAUC showed the same behavior: an increase at TP1 followed by a drop at TP2 as well as FU. The following changes reached statistical significance: T2w: BL-TP1(+20%), BL-TP2(-16%); iAUC: BL-FU(-29%); K trans : BL-FU(-55%), TP1-TP2(-32%). Conclusion First hybrid PET/MR results confirm previous results from serial MR and PET/CT, i.e. increasing ADC, K trans and iAUC in treatment week 2 correlates with morphological response. High FMISO uptake showed neither local stability nor persistency throughout the course of treatment. Final conclusions on quantitative PET/MR imaging for treatment response in cervix cancer requires a larger patient cohort. SP-0106 Reducing range uncertainties: new approaches for stopping power determination and in- vivo range verification K. Parodi 1 1 Ludwig Maximilians Universität München, Department of Medical Physics, München, Germany Radiation therapy with protons and heavier ion beams is a rapidly emerging treatment modality which promises precise delivery of a biologically effective dose to the tumour, with optimal sparing of surrounding critical organs and healthy tissue. To this end, over the last years, technological advances in beam delivery have been accompanied by an increasing integration and usage of imaging in the entire chain of fractionated treatment, from pre-treatment identification and characterization of the tumour up to anatomical guidance for patient positioning at the treatment site. Despite these recent technological advances, full clinical exploitation of the favorable ballistic properties of ion beams is still hampered by the yet unsolved problem of range uncertainties. To this end, new imaging approaches are being extensively investigated to tackle this issue at the stage of treatment planning or treatment delivery. In this contribution, special emphasis will be given to pre- treatment transmission imaging of multi-energy X-ray sources or energetic ion beams for refined assessment of the tissue stopping properties, as well as online/post- treatment detection of acoustic and nuclear-based emissions induced by ion interaction in tissue for in-vivo verification of the beam range. In particular, the main ongoing developments and initial pre-clinical or clinical experience will be critically reviewed, discussing the prospects of novel imaging methods for reducing range uncertainties in ion beam therapy. SP-0107 Mechanisms and Models of Particle Relative Biological Effectiveness (RBE) D.J. Carlson 1 1 Yale University School of Medicine, Therapeutic Radiology, New Haven- CT, USA Symposium: Innovations in ion beam therapy

All images were registered to neighboring time-points using RayStation (RaySearchLaboratories, Sweden) utilizing a hybrid deformable registration algorithm. Uterus, cervix, a reference structure for tumor to background ratio (TBR) calculation in gluteal muscle (GM) were delineated on all images. The GTV was defined on T2w images for the first 3 examinations. A sphere of 1cm diameter was created around the hottest voxel in the GTV of the PET to define the peak value. Datasets were assessed for tumor volume, enhancement kinetics (K trans ,