P03.11.B EFFECTS OF RADIOTHERAPY ON SYNAPTIC DENSITY AS ASSESSED BY [11C]UCB-J PET IN THE BRAINS OF PATIENTS WITH HEAD AND NECK CANCER

Abstract BACKGROUND Patients with head-and neck-cancer (HNC) often receive radiotherapy as part of their treatment. Due to the tumour location, exposure of the brain to irradiation is inevitable. Since the brain in HNC patients is not affected by an intracranial tumour, research in HNC patients can help to understand radiotherapy-induced effects on the brain which ultimately can help to improve treatment planning by optimizing radiation doses and avoiding more susceptible brain structures. [11C]UCB-J PET is a non-invasive method to assess synaptic density. This study aims to evaluate whether changes in synaptic density could be detected with [11C]UCB-J PET in patients with HNC treated with radiotherapy. MATERIAL AND METHODS Patients with HNC (nasopharynx, high grade parotid, oropharynx, skull basis or sinonasal cavity) that received radiotherapy (>50 Gy) as part of their regular treatment were subjected to [11C]UCB-J PET and T1w MRI at the start and 0-14 days after the end of radiotherapy. Standardized uptake values (SUV) were extracted from [11C]UCB-J PET for all regions within the Hammers brain atlas. Brain regions were grouped to their corresponding lobe and differences in synaptic density between start and end of radiotherapy were correlated to the radiation dose using Spearman correlations. RESULTS We included 8 patients with a mean age of 54.7±19.9 years. One was female and 7 male of which had 4 nasopharynx, 3 skull basis and 1 sinonasal tumour, and 3 received photon radiotherapy and 5 proton radiotherapy. All patients signed METc approved informed consent. From 151 evaluated brain regions, 77 received an average dose of >5 Gy, 43 received an average dose of >10 Gy, 12 received an average dose of >20 Gy, 6 received and average dose of >25 Gy, 0 received an average dose of >30 Gy. Significant correlations between differences in [11C]UCB-J PET uptake (SUV) between baseline and post-RT versus radiation dose were found for frontal lobe grey matter (GM) and white matter (WM) (r=0.502, p<0.001; 0.279, p<0.001, respectively), temporal lobe GM and WM (r=0.478, p<0.001; r=0.518, p<0.001), and occipital lobe GM and WM (r=0.332, p=0.021; r=0.298, p=0.04, respectively). CONCLUSION This [11C]UCB-J PET study suggest that a higher radiation dose seems to be associated with a lower synaptic density in the frontal lobe, temporal lobe, and occipital lobe in both WM and GM. These findings suggest that radiotherapy induces neuronal remodeling directly after treatment. FUNDING This study is financially supported by NWO with a VENI grant to Anouk van der Hoorn (no: 09150161910041).