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ESTRO 37

TMZ was compared to full dose RT in 6 weeks, showing similar results to the Nordic trial, with superiority of TMZ in the whole study population, and especially if the tumor was MGMT methylated. In both trials RT was better for patients with unmethylated tumor. The latest trial focusing on an elderly population (>65 years) with GBM was presented first time at ASCO 2016. The NCIC trial investigated hypofractionated RT of 40 Gy over 3 weeks with or without concomitant TMZ, the TMZ arm followed by maximum 12 adjuvant TMZ cycles. This study showed a significant survival benefit of the addition of TMZ, prolonging median survival from 7.6 to 9.3 months for the whole study population and for those with methylated MGMT, from 7.7 to 13.5 months, close to doubling survival. These trials show the importance of MGMT methylation status as a guide for treatment recommendations. For fit patients combined and hypofractionated treatment should be standard, while for frail patients, still felt to tolerate oncological treatment, single modality TMZ for those with methylated MGMT and short course RT for those with unmethylated MGMT can be offered. It is now important to find ways to better define which patient should be considered fit or frail, and for this the role of geriatric assessment, comorbidities, cognitive functioning and size of radiotherapy fields among other clinical factors, to further aid in therapeutic discussions with patients and their families and individualize the treatment of elderly with GBM. SP-0658 Recurrent glioblastoma: re-resection or re- irradiation? S. Scoccianti 1 1 Azienda Ospedaliera Universitaria Careggi, Radiation Oncology Unit, Firenze, Italy Abstract text Feasible local approaches for recurrent glioblastoma (GBM) in patients with a good performance status and unifocality of disease are second surgery (Re-S) or reirradiation (Re-RT). The aim of this talk is to define the impact of Re-S or Re- RT for recurrent glioblastoma and to identify prognostic factors that may help in selecting cases to treat. A second object of this presentation is providing practical answers to frequently asked questions for Re-RT of recurrent GBM. Several studies provide evidence for a longer overall survival in selected patients with recurrent glioblastoma who underwent Re-S or Re-RT, by contrast other studies report a limited impact in the clinical course. Comparison of these two salvage options is very difficult due to the scarcity of existing studies that directly compare the outcomes of the Re-S vs Re-RT. Also the interpretation of the single arm studies is very difficult due to the retrospective nature of the majority of the series with high risk of selection bias. Moreover, the extreme heterogeneity in baseline characteristics of the patients and the different measures of the outcome further complicate the analysis of the literature findings. At the same time, severe toxicity assessment is very difficult, especially for radiotherapy since the differentiation between tumor recurrence and radionecrosis after Re-RT may be very difficult, but also because most authors did not report the grade of toxicity. So, given these uncertainties, the key issue may be an appropriate selection of the patients that should be based on the prognostic factors that were proven to be important in literature: both patient-related factors (good performance status, age and RPA class) and recurrent disease-related factors (long time from the first course treatment to progression, possibility of gross total removal for surgery and target volume for radiotherapy) may help in selecting patients. Recently, some prognostic score indices were developed both for reirradiation and repeat surgery, in order to define patients who may have

a clearer benefit. Those indices are based on a combination of main prognostic factors (histotype, age, site of the disease, time from first course treatment, ependymal involvement) that may be used to predict patient survival. For patients with good prognostic factors, proper pre- retreatment risk estimate is fundamental to choose salvage local treatment: individual treatment decisions should not include only factors influencing the outcome, but also factors that may impact the potential morbidity of the treatment. On the one hand, the incidence of severe toxicity due to second surgery depends on recurrence site and, obviously, on comorbidities that may increase the anaesthesiologic risk. On the other hand, the incidence and severity of radiotoxicity can be increased by chemotherapy, age, diabetes. Additionally, disease- related factors may influence the risk of toxicity: lesion size, proximity to eloquent area or to organs at risk, overlapping with the target of the initial treatment are factors to take into account whenever a second irradiation is weighted against the surgical alternatives. An important advantage to consider surgery is the acquisition of tumor tissue at relapse. This may be valuable for differential diagnosis with radiation necrosis, confirmation of initial histology, definition of molecular markers of recurrent disease. By contrast, reirradiation may be a less invasive treatment. In this perspective, any attempt to reduce the expected toxicity of the treatment is extremely relevant. In this speech, existing data on the efficacy and toxicity of various Re-RT options including radiosurgery, hypo- fractionated stereotactic treatment, and conventionally fractionated RT will be reviewed. The literature will be thoroughly reviewed and the correlation between dose and response and between dose and toxicity will be here- in explored in order to define the optimal fractionation and prescription dose in terms of efficacy and tolerability. Moreover, some practical considerations for radiation treatment planning will be provided in order to improve the therapeutic ratio of the salvage treatment. SP-0659 MRI techniques for MR-only simulation N. Van den Berg 1 , M. Maspero 1 , A. Dinkla 1 , M. Savenije 1 , G. Meijer 1 , P. Seevinck 2 , J. Lagendijk 1 , B. Raaymakers 1 1 UMC Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands 2 UMC Utrecht, Centre for Image Sciences- Department of Radiology, Utrecht, The Netherlands Abstract text The increasing usage of MRI in the simulation process stems from its superior soft tissue contrast. This allows better delineation of tumor volume and OARs and thus contributes to overall improvement of treatment quality. As MRI does not provide direct information of the tissue electron density and bony anatomy for position verification, patients have to undergo two imaging exams in clinical practice: a CT and an MRI scan. Besides extra patient burden and medical costs, this introduces inevitable geometrical errors related to interscan differences and image fusion. This has been the rationale behind the development of MR-only simulation where all information needed for delineation, position verification and electron density is derived from MR images. A first prerequisite is of course the geometric fidelity of MR images. In the last two decades improvements in magnet design, gradient coils and image corrections have led to the possibility to perform geometrically accurate MR imaging for radiotherapy. Of course, this requires a quality assurance program to monitor geometrical fidelity Symposium: Advances in MRI simulation (MRI-only treatment planning)