ESTRO 37 Abstract book

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ESTRO 37

SP-0654 What is the limit of hypofractionation? M. Guckenberger 1 1 University Hospital Zürich, Department of Radiation Oncology, Zurich, Switzerland Abstract text The limit of hypo-fractionated radiotherapy for primary and secondary lung tumours is single-fraction radiosurgery. Prospective randomized studies comparing radiosurgery with fractionated SBRT for stage I NSCLC are promising for the single-fraction approach; however, long-term follow-up is missing and retrospective data suggest decreased efficacy compared to fractionated SBRT. Extreme hypo-hypo-fractionation for tumours with central or ultra-central does require risk-adapted fractionation, making the number of treatment fractions an additional degree of freedom in treatment planning. A major limitation is the current lack of validated dose constraints for many thoracic organs-at-risk, in particular in the setting of SBRT. SP-0655 How much do we know on the biology of extreme hypofractionation? B. De Bari 1 1 Hôpital Univ. Jean Minjoz CHU Minjoz Jeans & Belfort- Montbéliard Hospital, Radiation Oncology, Besançon, France Abstract text Radiobiological models usually applied for standard radiotherapy treatments (i.e. 1.8 – 2 Gy/fraction repeated in several fractions) are being challenged in the modern era of radiotherapy. On the one hand, the very good clinical results of stereotactic body radiotherapy, and on the other the impression that the α/β ratio for some cancers is not high (i.e. 10 Gy), but it may be of the same order (or even lower) than that adopted to calculate late complications, are some of the factors that are clearly influencing our knowledge about the tumor response to radiation. Some other factors that should be considered in evaluating the biological impact of extreme hypofractionation are the impairment of re-oxygenation between fractions, the very high α/β for hypoxic cells and the radiation induced vascular damage. All these aspects are probably more noteworthy when higher doses are delivered, and could complicate the analysis of clinical outcomes. Aim of this lecture will be to summarize available radiobiological evidences and the work in progress in the field of extreme hypofractionation.

GBM. The French study of Keime-Guibert found that for patients 70 years or older, 50 Gy was superior to best supportive care, prolonging survival from 4 to 7 months. A Canadian trial by Roa et al compared 60 Gy over 6 weeks versus 40 Gy in 3 weeks in 100 patients being 60 years or older, without finding a significant difference in survival. They later compared the same hypofractionated RT scheme of 40 Gy in 15 fractions to 25 Gy in 5 fractions, in 100 patients with poor performance status and age >50 years, also here without any clinically important difference in outcome. The Nordic trial randomized GBM patients 60 years or older between 60 Gy in 6 weeks or 34 Gy in 10 fractions over 2 weeks or temozolomide (TMZ) 200 mg/m2 days 1-5 q4 weeks, for 6 cycles. Best survival was noted for the TMZ arm, especially for patients with methylated tumor MGMT promotor and age >70 years. For those >70 years also hypofractionated radiotherapy over 2 weeks was superior to 60 Gy. In the German NOA-08 trial dose dense 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

Symposium: Brain tumors in 2018: are there still unsolved problems?

SP-0656 Two years since the release of new WHO classification of CNS tumors: what has come up new and how to implement this?

Abstract received

SP-0657 What is the best choice of therapy in elderly with GBM: concomitant chemoradiation, radiotherapy or chemotherapy? A. Malmström 1 1 Linköping University Division of Radiological Sciences, Institutionen för klinisk och experimentell medicin IKE / Avdelningen för Cellbiologi CELLB, Linköping, Sweden Abstract text During the last decade a number of important randomized clinical trials have been published, asking the question of best treatment for elderly, diagnosed with