ESTRO 37 Abstract book

S1165

ESTRO 37

Material and Methods Out of 56 glioblastoma patients treated with radiotherapy (dose 60 Gy in 30 fractions), five had recurrences extending outside the 95% isodose. The brain was segmented into white matter, grey matter and cerebrospinal fluid. Anatomic boundaries were delineated manually. A reaction-diffusion growth model was used assuming uniform proliferation throughout the brain and difference in white and grey matter diffusion of a factor of 10 with no migration across the barriers. The volume of image driven CTV (iCTV) corresponded to the standard CTV. The volumetric comparison was performed using the shortest distance (SD) between all surface points in the recurrence volume and respective CTV and iCTV. Results Three of five recurrences were distant, located in the temporal, parietal and frontal lobe. The median CTV and recurrence volume was 236 cm3 (range: 175-240 cm3) and 89 cm3 (range: 1-112 cm3), respectively. The median SD of the recurrence volume decreased from 7.0 mm (range: 4.7-36.0mm) for CTV to 5.5 mm (range: 2.9- 28.1mm) for iCTV indicating that iCTV was closer to the recurrence volume. However, distant recurrences were not included in either CTV or iCTV. Patient no. Vol CTV (cm3) Vol recur (cm3) Median SD-CTV (mm) Median SD-iCTV (mm)

cancer affects functional BM in the vertebral column. 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. Electronic Poster: Physics track: Images and analyses

1 (distant) 386 2 (distant) 200

112

8.5

5.5

1

36.0

28,1

3 (marginal) 4 (marginal)

240

101

5.1

2.9

236

89

7.0

4.3

5 (distant) 175 2.9 Table 1 : Patient specific volume data and corresponding surface distance (SD) between original clinical target volume (CTV) and the growth model driven CTV (iCTV) 1 4.7

Figure 1 : Patient example with recurrence (blue contour) outside the standard CTV (light yellow contour). The light green and purple contours correspond to the delineated GTV and the growth model image derived CTV (iCTV), respectively. A, B, C: Axial, coronal and sagital slice of T1w image overlaid with the compared structures and a tumor density map. The arrow indicates the location of distant recurrence for this patient. Conclusion The image driven CTV was found superior to predict marginal recurrences outside 95% isodose compared to standard CTV. However this population was limited in size and validation is warranted in a larger cohort. EP-2115 MRI visibility of gold fiducial markers for image-guided radiotherapy for rectal cancer R.P.J. Van den Ende 1 , L.S. Rigter 2 , E.M. Kerkhof 1 , E.L. Van Persijn van Meerten 3 , E.C. Rijkmans 1 , D.M.J. Lambregts 4 , B. Van Triest 5 , M.E. Van Leerdam 2 , M. Staring 6 , C.A.M. Marijnen 1 , U.A. Van der Heide 1 1 Leiden University Medical Center, Department of Radiation Oncology, Leiden, The Netherlands 2 Netherlands Cancer Institute, Department of Gastroenterology, Amsterdam, The Netherlands