ESTRO 36 Abstract Book

S122 ESTRO 36 _______________________________________________________________________________________________

0.15) as compared with patients with mild (median fraction of injured lung = 0.06) or no dyspnea (median fraction of injured lung = 0.04) as seen in the top left panel of the figure showing boxplots of the overall fraction of injured lung in the three groups of patients. Similar results were found when dividing the radiological injuries in categories based on appearance (see the last three panels in the figure). Patients with severe dyspnea had a significant higher fraction of interstitial changes or ground-glass opacities in the lung as compared with patients with no dyspnea, while the severe and mild groups only were borderline different. The fraction of lung with consolidation injury was low and did not significantly differ between patient groups.

hypoxic tumors. The underlying reason for this is that the oxygen enhancement ratio (OER) is smaller for 12 C-ions than for photons. However, there is a lack of in vivo evidence for a decreased OER of 12 C-ions relative to photons. To investigate the impact of hypoxia, dose- response curves for photons and 12 C-ions were determined for R3327-HI rat prostate adenocarcinomas under ambient and acute hypoxic conditions. Material and Methods Tumor fragments of a Dunning prostate tumor R3327-HI were transplanted s.c. into the distal thigh of male Copenhagen rats. Tumors were treated with increasing doses of either 12 C-ions or 6 MeV photons under ambient or acute hypoxic conditions. Acute hypoxia was induced by clamping the feeding artery 10 min before and during treatment. Primary endpoint was local tumor control within 300 days. OER-values for ambient vs. hypoxic conditions for both irradiation modalities as well as RBE- values were calculated based on TCD 50 -values (dose at 50% tumor control probability) of photons and 12 C-ions, respectively. Results Local tumor control was achieved with 12 C-ions and photons under normoxic as well as hypoxic conditions, however, a higher effectiveness was obtained for 12 C-ions. The RBE for local tumor control after single dose irradiation increased from ambient conditions (2.08±0.13) to hypoxic conditions (≈2.5). The OER was significantly smaller for 12 C-ions than for photons, but both values were lower than the OER-values measured under cell culture conditions. Since some animals are within their 300 days follow-up, precise OER-values are still pending. Conclusion The RBE of 12 C-ions increases under hypoxic conditions, since the OER of 12 C-ions is significantly lower than for photons. Interestingly, the OER for both radiation qualities was much lower than measured in vitro . This supports the need of in vivo experiments to assess the impact of hypoxia in patients treated in heavy ion radiotherapy. OC-0243 Submicron focused proton irradiation – understanding the RBE of heavy ion irradiation T.E. Schmid 1,2 , C. Greubel 3 , K. Ilicic 2 , D. Walsh 3 , J. Reindl 3 , C. Siebenwirth 2 , J.J. Wilkens 2 , G. Multhoff 2 , E. Schmid 4 , G. Dollinger 3 , S.E. Combs 1,2 1 Helmholtz Zentrum München, Institute of innovative Radiotherapy, Neuherberg, Germany 2 Klinikum rechts der Isar, Radiooncology, München, Germany 3 Universität der Bundeswehr München, Applied Physics, Neubiberg, Germany 4 University of Munich, Department for Anatomy and Cell Biolog, München, Germany Purpose or Objective High LET radiation like heavy ions is well known to induce a higher relative biological effectiveness (RBE) than low LET radiation. The dependence of RBE with LET is of special interest for heavy ion tumor therapy and for radiation safety issues. Irradiations with low and high LET particles differ in the spatial dose distribution. Only a few high LET particles hit a cell nucleus and deposit doses of a few gray where the dose deposition and thus the DNA damage concentrates around the few ion trajectories. In contrast several hundred low LET particle hits are needed to achieve the same dose resulting in a quasi- homogeneous damage distribution. The influence of different spot sizes is studied on the induction of dicentric chromosomes. Material and Methods Human-hamster hybrid (AL) cells were irradiated with focused 20 MeV protons in a quadratic matrix pattern with point distances of 5.4×5.4 µm2 and 117 protons per matrix point at the ion microbeam SNAKE using different spot- sizes between 0.8 and 2.7 µm (full width at half

Conclusion The fraction of lung with radiological injuries after radiotherapy was higher in patients with severe dyspnea as compared to mild or no dyspnea. Dividing the radiological injury based on appearance did not increase the association with clinical symptoms. The radiologic endpoint provides supplementary information in patient outcome assessment and could be attractive for radiobiological response modelling as an objective endpoint disentangled from medical commodities.

Proffered Papers: Understanding RBE and its relevance in vivo

OC-0242 The oxygen enhancement ratio for carbon ions is smaller than for photons in R3327-HI prostate tumors C. Glowa 1,2,3 , P. Peschke 2,4 , S. Brons 5 , P. Huber 1,2,4 , J. Debus 1,2 , C. Karger 2,3 1 University Hospital Heidelberg, Department of Radiotherapy and Radiation Oncology, Heidelberg, Germany 2 National Center for Radiation Research in Oncology NCRO, Heidelberg Institute for Radiation Research in Oncology HIRO, Heidelberg, Germany 3 German Cancer Research Center, Department of Medical Physics in Radiotherapy, Heidelberg, Germany 4 German Cancer Research Center, Clinical Cooperation Unit Molecular Radiooncology, Heidelberg, Germany 5 Heidelberg Ion Beam Therapy Center, Heidelberg Ion Beam Therapy Center, Heidelberg, Germany Purpose or Objective Carbon ions ( 12 C-ions) show an increase d relative biological effectiveness (RBE) relative to photons and cell culture experiments exhibit a higher RBE especially in