ESTRO 36 Abstract Book

S333 ESTRO 36 _______________________________________________________________________________________________

Results The median and mean volumes of T1Gd-MRI-GTVs were 7.71ml (range 0.95–48.27ml) and 10.67 ± 9.33ml, respectively. ADC low volumes were significantly smaller (median 1.68ml (range 0.27–7.25ml) and mean 2.43 ± 1.85ml, p <0.001). The ADC low / T1Gd-MRI overlap volume ranged from 0.03-3.25ml (median 0.62ml) with a mean volume of 0.84 ± 0.85 ml. The corresponding ADC low /T1Gd- MRI-GTV non-overlap volume was 1.46 ± 1.22ml ( p =0.0053) with a median of 1.14ml (range 0.09-5.58ml). Conclusion The results of this study suggest that GTV delineation according to contrast enhancement in T1Gd-MRI in patients with recurrent GBM may lead to target volumes that do not encompass all biologically active tumor detectable in advance DWI MR imaging. Retrospective correlation of ADC low areas with the respective isodose distribution and topography of further progression after re-irradiation will help to understand the clinical significance of ADC low /non-Gd enhancing areas. PO-0637 HFSRT to the resection bed for intracranial metastases: a large retrospective study of 181 patients. A. Keller 1 , M. Doré 2 , F. Thillays 2 , F. Proust 3 , H. Cebula 3 , I. Darié 3 , F. Lefebvre 4 , G. Noel 1 , D. Antoni 1 1 Centre Paul Strauss, Radiotherapy, Strasbourg CEDEX, France 2 Institut de Cancérologie de l'Ouest, Radiotherapy, Saint Herblain, France 3 CHU Hautepierre, Neurosurgery, Strasbourg, France 4 Faculty of Medecine, Laboratory of Biostatistics, Strasbourg, France Purpose or Objective We retrospectively report the outcomes of a large multicenter cohort of patients treated with surgery and hypofractionated stereotactic radiotherapy (HFSRT) to the resection cavities of brain metastases (BM). Material and Methods Between March 2008 to February 2015, a total of 181 patients (189 cavities) with no prior WBRT were treated by HFSRT to the surgical bed of BM, at the dose of 23.1 Gy (3 x 7.7 Gy) prescribed to the 70 % isodose line (with 2- mm margin PTV). The primary end-point was local control. Secondary endpoints were distance brain control, overall survival, risks of radionecrosis (RN) and leptomeningeal disease (LMD). Results Of the 189 resected lesions, 44 % were metastatic from a non-small cell lung cancer (NSCLC) primary tumor and 138 patients (76.2 %) had a single metastasis at the time of treatment. The median preoperative tumor volume was 12 mL (0,13 - 92,5), and the median PTV 14.1 mL (0,8 - 65,8). With a median follow up of 15 months (0.6 – 75), the 6- and 12- month local control rates were 92.6 % [95 % CI: 88.8 - 96.3] and 88.2 % [83.6 - 92.9], respectively. On multivariate analysis, PTV (HR = 1.03 [1.01 - 1.05], p = 0.005) and GPA (Graded Prognostic Assessment) score (HR = 2.02 [1.11 - 3.66], p = 0.021) were predictive of local failure. The 6-, 12-month distance brain control rates were 70.4 % [63.9 - 76.8] and 60.7 % [53.7 - 67.7], respectively. Twenty-six patients (14.4 %) developed signs of LMD, at a median time of 3.8 months (0.13 - 33.6) after HFSRT. Preoperative tumor volume was predictive of LMD (HR = 1.02 [1.0 – 1.04], p = 0.029). The median overall survival (OS) was 17.3 months (0.59 - 65.9). The 6-, 12- and 24-month OS rates were 78.8 % [73.2 - 84.9], 62.5 % [55.9 - 69.9] and 39.1 % [32.4 - 47.2], respectively. RPA Class 3 (HR = 2.05 [1.12 - 3.76], p = 0.02), piecemeal resection (HR = 1.56 [1.09 – 2.27], p = 0.017) and increasing number of BM (HR = 1.71 [1.34 - 2.16], p < 0.0001) were independent unfavorable prognostic factors for OS. Fifty-four patients (29.8 %) were subsequently treated with salvage WBRT at a median time of 6.5 months (0.4 - 44.9), and among the patients who developed

Conclusion In this small series of consecutive CNS tumor patients, psychological support during radiotherapy allows an improvement in distress. Quality of life remained stable with a significant improvement of emotional well-being. PO-0636 Impact of DWI-MRI for gross tumor volume definition in patients with recurrent glioblastoma O. Oehlke 1 , S. Bott 1 , A.L. Grosu 1 , I. Mader 2 1 Universitatsklinik Freiburg, Klinik für Strahlenheilkunde, Freiburg, Germany 2 Universitatsklinik Freiburg, Klinik für Neuroradiologie, Freiburg, Germany Purpose or Objective The low specificity of gadolinium-enhancement in T1- weighted MRI (T1Gd-MRI) in the definition of gross tumor volume (GTV) in recurrent glioblastoma (GBM) is a clinically important problem in the context of treatment planning for re-irradiation. Advanced MR imaging techniques like diffusion-weighted imaging (DWI) have been introduced for diagnosis of tumors. Tumors demonstrate restricted diffusion and thus low apparent diffusion coefficient (ADC), which inversely correlates with tumor cellularity. The goal of this study was to evaluate possible ADC low /T1Gd-MRI non-overlap volumes that may have an impact on definition of the GTV in patients with recurrent GBM planned for stereotactic re- irradiation. Material and Methods We evaluated 41 patients treated with stereotactic re- irradiation for recurrent GBM. All patients initially received standard of care with resection followed by radiochemotherapy and adjuvant temozolomide. Progression was diagnosed either by re-resection, biopsy, or RANO criteria in serial MR images. The T1Gd-MRI-GTV was defined as contrast enhancement in 3D T1-weighed sequences. The DWI data were acquired by using a singleshot spin-echo echo-planar imaging sequence ( b =0, 1000 s/mm 2 ). ADC values are automatically calculated and displayed as a parametric map. In order to minimize bias, T1Gd-MRI-GTV and ADC low areas were determined by different persons.