ESTRO 38 Abstract book

S378 ESTRO 38

Aarhus, Denmark ; 2 Aarhus University Hospital and Aarhus University, Department of Oncology and Department of Psychology and Behavioral Sciences, Aarhus, Denmark ; 3 Northwestern University Feinberg School of Medicine, Department of Medical Social Sciences, Chicago, USA ; 4 Aarhus University Hospital, Department of Neurosurgery, Aarhus, Denmark ; 5 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark Purpose or Objective To assess cognitive function in patients with a primary brain tumour treated with radiotherapy (RT). The extent of RT-induced changes in cognitive function is unknown. RT with protons instead of photons spares more healthy brain tissue and may reduce the risk of cognitive dysfunction; however, existing knowledge regarding the parts of the brain that need to be spared to prevent cognitive dysfunction, is limited. To determine the cognitive domains most affected by RT, we compared cognitive functioning in brain tumour patients treated with neurosurgery and RT with brain tumour patients treated with neurosurgery only. Furthermore, we investigated the correlations between cognitive scores and RT dose-volume parameters in specific areas of the brain. Material and Methods A cross-sectional study assessing cognitive function in 110 patients with a primary brain tumour grade I-III or medulloblastoma (grade IV) treated at Aarhus University Hospital (AUH), Denmark, between 2006 and 2016. Two cohorts were established: A cohort of 81 brain tumour patients who had received neurosurgery followed by RT (RT+) and a cohort of 29 brain tumour patients who had only received neurosurgery (RT-). The patients completed questionnaires and underwent neuropsychological assessment with standardized tests. RT dose-volume histogram (DVH) of specific areas in the brain were extracted from the treatment plans to explore correlations between dose-volume parameters and cognitive scores. Results Mean age was 53.5 years with an average time since diagnosis of 7.3 years. Compared with normative data, lower average scores were observed for the entire group in the following domains: verbal learning and memory ( p <0.001), attention and working memory ( p <0.001), processing speed ( p <0.001), and executive functioning ( p <0.001). Compared to RT- patients, RT+ patients scored lower on domains concerning processing speed (p=0.04) and executive function (p= 0.05) and had higher impairment frequency on verbal fluency (p=0.02) with 16% of patients exceeding 1.5 SD below the normative mean. At time of analysis, 52 RT+ patients’ DVH of the left hippocampus was extracted. When examining scores on Hopkins Verbal Learning Test (HVLT), a test assessing verbal learning and memory, higher RT dose to the hippocampus was correlated with the number of people with impaired scores on HVLT. Conclusion Our results indicate that treatment, including RT, for a primary brain tumour may have negative long-term impact on cognitive function, especially on processing speed and executive function. Preliminary data suggest that higher RT dose to the left hippocampus is associated with greater verbal learning and memory impairment. PO-0736 Radiation necrosis after a combination of EBRT and iodine-125 brachytherapy in gliomas I. Hadi 1 , D. Reitz 1 , R. Bodensohn 1 , O. Roengvoraphoj 1 , M. Niyazi 1,2 , C. Belka 1,2 , F. Kreth 3 , S.B. Nachbichler 1 1 University Hospital- LMU Munich, Department of Radiation Oncology, Munich, Germany ; 2 German Cancer Consortium DKTK, Department of Radiation Oncology,

Munich, Germany ; 3 University Hospital- LMU Munich, Department of Neurosurgery, Munich, Germany Purpose or Objective The frequency and the risk profile of radiation necrosis in patients with glioma undergoing either upfront stereotactic brachytherapy (SBT) and additional salvage external beam radiotherapy (EBRT) after tumor recurrence or vice versa remains unknown. Material and Methods Patients with glioma treated with low-activity temporary iodine-125 SBT between 1999 and 2016 who had either additional upfront or salvage EBRT were included. Biologically effective doses were calculated. Radiation necrosis was diagnosed using stereotactic biopsy and/or metabolic imaging. The rate of radiation necrosis was estimated with the Kaplan Meier method. Risk factors were obtained from logistic regression models. ROC and AUC analyses were used to determine optimal cut-off values for identified risk factors.

Results Eighty-six patients (49 male, 37 female), with a median age of 47 years were included. Median follow-up was 15.0 months after second irradiation treatment. Fifty-eight patients received upfront EBRT (median total dose: 60 Gy), and 28 patients upfront SBT (median reference dose: 54 Gy, median dose rate: 10.0 cGy/h). The median time interval between both treatments was 19 months. In 8/75 (10.7%) patients a radiation necrosis was diagnosed. The one- and two- year risk of radiation necrosis was 5.1% and 11.7%, respectively. The logistic regression models indicated tumor volume of SBT (Fig.a) , irradiation time of SBT (Fig.b) , number of implanted seeds, and salvage EBRT as significant risk factors for radiation necrosis. Neither of the BED values nor the time interval between both treatments gained prognostic influence.

Conclusion The combination of upfront EBRT and salvage SBT or vice versa is feasible for glioma patients. The risk of radiation necrosis is mainly determined by the treatment volume but not by the interval between the therapies. PO-0737 Retrospective analysis of hypofractionated stereotactic radiotherapy for tumors larger than 2 cm