ESTRO 37 Abstract book

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ESTRO 37

2 Fortis Memorial Research Institute, Radiology, Gurgaon, India Purpose or Objective Radiation therapy (RT) is a mainstay of treatment for primary and metastatic brain tumours. Various toxicities, ranging from asymptomatic to fatal, occur in the central nervous system after RT to the brain. MR imaging is useful in detecting these toxicities and complications. White matter changes in the brain after RT is well-known and is seen on T2-weighted or FLAIR MR images. The purpose of this study was to evaluate post-RT imaging changes using FLAIR T2-weighted MR images in adult primary brain tumour patients previously treated with RT. We aimed to see if any correlation existed between isodose of the delivered doses and subsequent T2 changes post-RT. Material and Methods Between Sept.2012 and Dec.2016, we retrospectively analysed records of all newly diagnosed low grade brain tumours who received RT to brain (with/without concurrent Temozolomide- TMZ). Fourteen patients who had MR images consisting of T2/FLAIR sequences, available from 6-24 months after RT completion were taken for the final analysis. In all patients RT was initiated 4-6 weeks after surgery/biopsy. Two patients were treated using IMRT while 12 patients were treated using partial arc VMAT. Concurrent TMZ to a dose of 75mg/m2 was given in 6 patients. Imaging datasets 6-24 months post-RT were analysed. The MR sequences included T2-FLAIR weighted images with a slice thickness of 2-3mm, which was reviewed by a radiologist and a radiation oncologist. These images were then fused with RT planning MRI on the BrainLab (BrainLab AG, Feldkirchen, Germany).The identified white matter changes were contoured on the FLAIR sequences. The MR images prior to RT were also reviewed to exclude pre- existing hyperintensity related to peritumoral edema, tumour infiltration or post-operative changes. Results Final analysis included 14 patients. Median age was 48.5yrs (3-63yrs) at time of RT. Histological diagnoses were astrocytoma (n=10), oligodendroglioma(n=3) and ependymoma(n=1). One patient had grade 1 histology while all others had grade 2 histology. Median dose was 55.9Gy (45 - 60Gy) at 1.8- 2Gy per fraction, 5 days a week. Mean PTV volume (vol.) was 305.6±358.6cc (32.5 - 1461.4cc). Mean vol. of the contoured T2 changes was 60.9±54.9cc (0.93 - 145cc). Percentage isodose encompassing 100% of T2 change vol. was 63.3±28.5% (19 - 98.7%) but there was no significant correlation between the delivered dose to the PTV and the percent isodose (p=0.61). There was however, a significant correlation between the PTV and the T2 change vol. (p=0.02). Conclusion This retrospective analysis showed that though there was significant post-RT T2 changes in the brain parenchyma, these changes were not confined to any specific isodose but were distributed from low to high dose regions. It will be imperative to study further if post-RT changes on T2- FLAIR carry significance in terms of white matter changes, which can bear correlation to toxicities vis-a-vis residual disease progression or recurrence. EP-1204 Limited margin radiotherapy and temozolomide for glioblastoma multiforme: pattern of failure S. Sastre-Gallego 1 , E. Fernández-Lizarbe 1 , M. Martín- Sánchez 1 , E. Carrasco-Esteban 1 , R. Hernanz-De Lucas 1 , P. Barrionuevo-Castillo 1 , S. Sancho-García 1 1 Ramon y Cajal University Hospital, Radiation Oncology, Madrid, Spain

Purpose or Objective The aim of this retrospective study was to evaluate our experience treating patients diagnosed of glioblastoma multiforme (GBM) according to ESTRO-ACROP guidelines and to evaluate our pattern of failure using their target delineation recommendations. Material and Methods we analysed 28 patients, 57% male (16p) and 43% female (43%), diagnosed of GBM treated between 20 15 and 2017. We used standard fractionation to a total dose of 60Gy with concurrent Temozolomide (85.7%), hypofractionated RT to a total dose of 40.05Gy with concurrent TMZ (10.7%) or hypofractionated RT alone (3.5%). The clinical target volume (CTV) includes T1- enhancing tumor and resection cavity without inclusion of peritumoral edema with a margin of 2cm reducing anatomical barriers. The volume of recurrent tumor was categorized within 60 Gy isodose line as central (>80%), marginal (20-80%) or distant (<20%) failure. Results With a median follow up of 11.5 months, 12 patients (42%) developed tumor progression. We observed 83% central failure (10p), 8% marginal failure (1p) and 8% both central and marginal failure (1p). None distant recurrence was reported. We delineated a new CTV including peritumoral edema for the patient with marginal failure to evaluate if we could have avoided the recurrence with wider margins. The recurrence would have been marginal even with a Not including peritumoral edema and using reduced margins did not appear to increase the risk of marginal and distant failure. Thus, we can safely treat our patients by irradiating less healthy tissue. This reduction may lead to dose escalation schemes without increasing organs at risk irradiation. EP-1205 Spine SABR with simultaneous integrated boost using Cyberknife®: Clinical outcomes L. Schiappacasse 1 , R. Jumeau 1 , G. Saliou 2 , N. Ruiz-Lopez 3 , V. Vallet 3 , S. Alshehri 1 , E. Ozsahin 1 , J. Bourhis 1 1 Centre Hospitalier Universitaire Vaudois, Department of Radiation Oncology, Lausanne Vaud, Switzerland 2 Centre Hospitalier Universitaire Vaudois, Department of Radiology, Lausanne Vaud, Switzerland 3 Centre Hospitalier Universitaire Vaudois, Institute of Radiophysics, Lausanne Vaud, Switzerland Purpose or Objective Spine stereotactic ablative radiotherapy (SABR) has became a new tool in the management of metastatic patients. This technique provides higher local control rates than conventional palliative therapies. This study’s aim was to show the efficiency and feasibility of spine SABR with simultaneous integrated boost using Cyberknife ® . Material and Methods A retrospective analysis of patients with spinal metastases treated with SABR at our institution was conducted. All patients had planning computed tomography (CT) and dedicated magnetic resonance imaging (MRI). The gross tumor volume (GTV) of each spinal metastasis was contoured on the T1- and T2- weighted MRI sagittal sequence. Each clinical target volume (CTV) was delineated according to the international spine radiosurgery consortium consensus guidelines. An additional margin of 1 mm was added to the CTV to create the planning tumor volume (PTV) and to the GTV to create the PTV boost. All patients were treated with Cyberknife ® , tumor tracking was achieved using the Xsight spine tracking system. The overall survival (OS) and the local control were described using Kaplan-Meier statistics. larger PTV. Conclusion