ESTRO 2021 Abstract Book

S893

ESTRO 2021

HSRT appears to be feasible, effective and well tolerated. As shown, both radiotherapy centers decided to increase the total dose above 50 Gy 10 (27Gy/3 or 35/5 fractions) in order to improve the outcomes as emerging from the literature data. Nevertheless we didn’t find a dose-response correlation in terms of LC and OS, probably due to the small size of sample and the retrospective analysis.

PO-1072 FSR for arterio-venous malformations: a single-centre retrospective study. R. Ching-López 1 , S. Rodríguez 1 , P. Vargas 1 , M. Zurita 1 , R. del Moral 1 , J. Expósito 1 1 Hospital Virgen de las Nieves, Radiation Oncology, Granada, Spain

Purpose or Objective To analyze the experience in our centre treating arteriovenous malformations (AVMs) using fractionated stereotactic radiotherapy (FSR) with a hypofractionated scheme. Materials and Methods Between February 2011 and June 2015, 30 patients diagnosed with Spetzler and Martin grade IV-V arterio- venous malformations (AVMs) were treated in our centre with FSR. The median age at treatment was 41 years (range 15-73), 18 men and 12 women, in good general condition (ECOG 0-1). In most patients, the location of the AVM was left parietal. Before radiotherapy treatment, embolization was performed in 6 patients, radiosurgery in 6 patients, and surgery in 2 patients; in the rest, radiotherapy treatment was administered exclusively. The most used fractionation scheme was from 30Gy to 6Gy per fraction, 5 fractions per week in 76.7% (23 patients). Results With a median follow-up of 82 months (range 42-175 months), 6 complete responses were detected, a partial response in 16 patients, one of whom died from bleeding secondary to the malformation, and stabilization in 8 patients. From the symptomatic point of view, 16 patients remain stable, 5 asymptomatic, 6 with symptomatic improvement and 2 with worsening of symptoms. The treatment was very well tolerated, more than 80% of the patients did not present acute toxicity and those that did it were mild and controlled with formacological treatment. As a late effect of treatment, radionecrosis was detected in 4 patients, 1 of whom received previous treatment with radiosurgery. Conclusion Considering that treatment with FSR is reserved for patients with complicated AVMs, our results support the usefulness of such a treatment scheme with great tolerance and adequate disease control. PO-1073 Feasibility of the APRICOT-trial: identifying MRI biomarkers for radiation-induced cognitive changes E. van Grinsven 1 , A. Bhogal 2 , J. Guichelaar 2 , J. Siero 2,3 , H. Hoogduin 2 , M. van Zandvoort 1,4 , J. Verhoeff 5 , M. Philippens 5 1 University Medical Center Utrecht, Department of Neurology & Neurosurgery, Utrecht, The Netherlands; 2 University Medical Center Utrecht, Department of Radiology, Utrecht, The Netherlands; 3 University of Amsterdam, Spinoza Centre for Neuroimaging, Amsterdam, The Netherlands; 4 Utrecht University, Department of Experimental Psychology and Helmholtz Institute, Utrecht, The Netherlands; 5 University Medical Center Utrecht, Department of Radiotherapy, Utrecht, The Netherlands Purpose or Objective Radiotherapy (RT) is a standard treatment for patients with brain metastases (BMs), although it may lead to radiation-induced cognitive impairment. Since overall survival time is often limited, maintaining adequate quality of life during the remaining life span is pivotal and influences treatment shared decision making. It is currently not possible to predict the impact of RT on individuals as the pathogenesis of cognitive impairment is not fully understood. The main goal of the APRICOT-trial is to identify MRI-derived biomarkers for radiation- induced cognitive impairment three months after RT in BMs patients. The aim of the current pilot-study is to assess the feasibility of the APRICOT protocol. Materials and Methods In the APRICOT-trial a total of 69 patients will receive a 90-minute neurocognitive assessment (NCA) and series of MRI scans to derive vascular parameter maps. These include blood oxygen level-dependent (BOLD) MRI for cerebrovascular reactivity (CVR) during elevated CO 2 breathing and blood volume/metabolic information during O 2 breathing, multi-delay ASL for arterial arrival time and perfusion, resting-state for temporal signal to noise (tSNR) and low-frequency fluctuation data (fALFF), and finally T2FLAIR, T1w and susceptibility weighted imaging (SWI). Data was processed using in-house analysis pipelines to yield a series of parameter maps that were spatially co-localized with RT dose and contoured target volumes. Both the NCA and MRI are performed pre-RT and three months post-RT. The data of the first five patients with complete follow-up will be examined to assess feasibility of the protocol in BMs patients and to identify changes in brain tissue status. Results Four months after study start, six of ten eligible patients (56-81yrs; 3f) completed pre-RT measurements. Three patients also returned for post-RT measurements. All six patients completed the entire NCA. The CO 2 /O 2 breathing challenges were well-tolerated by all but one patient. Parameter maps revealed lower CVR and longer hemodynamic lags, indicating vascular impairment in tumor and tumor-surrounding regions (see Fig1). Affected regions correlate with hyper-intensities in the T2Flair/tSNR and hypo-intense regions in the O 2 maps; indicating low perfusion or blood volume or potential disease-related neuronal dysfunction (fALFF). Combining these MRI-derived parameters allows to identify subtle changes in brain tissue status, that are not visible on conventional MRI.