Abstract Book

S1162

ESTRO 37

This was evaluated by employing 2-deoxy-2-(18F)fluoro- D-glucose (18F-FDG) positron emission tomography (PET) prior to, during, and after fractionated radiotherapy (RT). Material and Methods Twenty-six patients with advanced NSCLC, receiving RT (10×3 Gy) alone or concomitantly with erlotinib, were examined by 18F-FDG PET before, during, and after treatment. A total of sixty-one 18F-FDG PET scans were analyzed. Vertebral column BM 18F-FDG uptake normalized to the liver, SUV BMLR , and was evaluated at the three PET sessions. Analyses were done based on vertebral column, cervical, thoracic, and lumbar vertebrae. Moreover, the effect of high radiation dose (> 10 Gy) and erlotinib were investigated. Change in the pre-therapy SUV BMLR among all vertebrae was analyzed using single factor ANOVA. Wilcoxon signed-rank test was used to assess changes in BM uptake of 18F-FDG between sessions. Any possible effects of erlotinib on the BM activity during and post-treatment were assessed using Mann Whitney U test. Results A homogeneous distribution of 18F-FDG uptake was observed within vertebral column prior to treatment (p= 0.2). Mean SUV BMLR (±SEM) in the vertebral column at pre-, mid-, and post-therapy was 0.66±0.03, 0.61±0.03, and 0.62±0.03 respectively. Mean SUV BMLR (±SD) for thoracic vertebrae received total RT dose of 10 Gy or more was 0.64±0.15, 0.56±0.09, and 0.59±0.12 at pre-, mid-, and post-therapy, respectively. A significant reduction in SUV BMLR was observed from pre- to both mid- and post- therapy (p<0.05). SUV BMLR was significantly high at post- therapy compared to mid-therapy (p<0.05). An increasing trend in the SUV BMLR was seen for the lumbar and cervical vertebrae, located in the low-dose region, after one week of treatment that could result from a compensatory effect (Figure 1). This increase, however, was not significant. Vertebral column SUV BMLR was higher in patients receiving erlotinib post-therapy (p=0.01). Conclusion Radiotherapy reduces BM 18F-FDG uptake in the vertebral column, especially in high dose region, pointing to subsequent hematologic toxicity. Concomitant erlotinib stimulates a recovery in BM 18F-FDG uptake from mid- to post-therapy. EP-2114 Prediction of recurrence patterns using diffusion driven growth modelling for glioblastoma. J. Kallehauge 1 , M. Lundemann 2 , P. Munck af Rosenschold 2 , M.B. Jensen 1 , S. Lukacova 3 1 Aarhus University Hospital, Department of Medical Physics, Aarhus C, Denmark 2 Rigshospitalet, Department of Oncology Section for Radiotherapy, Copenhagen, Denmark 3 Aarhus University Hospital, Department of Oncology, Aarhus C, Denmark Purpose or Objective Clinical target volume (CTV) for radiotherapy of glioblastoma is typically defined as an isotropic 2 cm expansion to the area of residual enhancement on T1 weighted MR imaging plus the surgical bed. Tumor growth models allow for incorporating the biological information about preferential spread along the white matter fibers in target definition. The aim of the study was to assess the value of an image driven CTV in the prediction of non-central recurrences. Material and Methods Out of 56 glioblastoma patients treated with radiotherapy (dose 60 Gy in 30 fractions), five had recurrences Electronic Poster: Physics track: Images and analyses

These slopes were used to correct to model coefficients prior to signature validation. The results of validation are shown in Table 1.

Conclusion The radiomic signature remains prognostic for NSCLC even after large erosion of the original GTV, provided that new model coefficients are derived based on a linear correction factor of the radiomic features. This implies that prognostic information is still captured and in the center of the GTV. This makes it possible to reduce the interobserver variability between delineations which will improve the reproducibility of radiomics. Moreover, these results will help to reduce the workload for the cumbersome delineation process, which is especially important for longitudinal or delta radiomics approaches were tumor shrinkage plays a role or datasets where no tumor lesions are delineated (e.g. non-radiotherapy). EP-2113 Reduction in the bone marrow 18F-FDG uptake during thoracic radiotherapy of lung cancer A. Abravan 1 , H. Eide 2 , A.M. Løndalen 3 , A. Helland 4 , E. Malinen 5 1 University of Oslo, Department of Physics, Oslo, Norway 2 Oslo University Hospital, Department of Oncology-, Oslo, Norway 3 Oslo University Hospital, Department of Radiology and Nuclear Medicine-, Oslo, Norway 4 Oslo University Hospital, Institute for Cancer Research-, Oslo, Norway 5 University of Oslo, Department of Physics-, Oslo, Norway Purpose or Objective Both cancer and cancer treatment can affect bone marrow (BM) metabolism, which may further contribute to hematologic toxicity. In this study, we longitudinally assessed how treatment of advanced non-small cell lung cancer affects functional BM in the vertebral column.