Abstract Book

ESTRO 37

S586

(0, 5, 10, 15, 20 and 30 Gy) at two positions along the proton depth-dose curve (at the plateau and at the middle of Spread Out Bragg Peak ), furthermore, with reference linear accelerator photon (0, 5, 10, 15, 20 Gy) beams (n=96 in each group), repeated several times (≥3). Thereafter, survival, any type of organ developmental disturbance (pericardial edema, spine curvature, shortening of the body length and micro-opthalmia) were detected each days up to 7 post irradiation days (pid). Histological evaluation (size of the eye, brain necrosis, intestinal changes, liver vacuolization, hyper eosinophilic necrotic muscle-fibers) and molecular changes were evaluated with RT-PCR method at certain time points post irradiation. Results A higher vulnerability and radiation sensitivity could be observed at earlier stages of the embryogenesis (1-12 hpf). The LD 50 was determined with the well reproducible survival curves, resulting in a relative biological effectivity (RBE) between 10 and 4.8 for the 1 MeV and 14 MeV neutrons and around 1.1-1.4 for protons at the two positions, respectively. The morphological distortions shown close correlation to the dose delivered and their evaluation on the 4 th pid exhibited a good agreement to the survival derived RBE. The gravity of the histopathological changes on the basis of semi- quantitative analysis corresponded well to the macro morphological abnormalities (eye layer disorganization, degree of brain necrosis, increased numbers of the goblet cells in the gastrointestinal tract, and muscle fibrosis). Conclusion Numerous features of the zebrafish embryo model makes it amenable for large scale of radiobiological investigations. On the basis of our experimental series the optimal embryonal age (hpf), radiation setup and observation time points for assessment of the different biological endpoints could be established. The defined parameters proved to be suitable for reliable RBE determination. PO-1044 In vivo imaging of microvascular changes in irradiated oral mucosa by optical coherence tomography A. Maslennikova 1 , M. Sirotkina 2 , E. Sedova 3 , A. Moiseev 4 , S. Ksenofontov 4 , G. Gelikonov 4 , L. Matveev 4 , E. Kiseleva 2 , V. Zaitsev 4 , E. Zagaynova 2 , F. Feldstein 2 , N. Gladkova 3 , A. Vitkin 5 1 Regional Oncology Hospital, Radiation therapy, Nizhny Novgorod, Russian Federation 2 Nizhny Novgorod State Medical Academy, Institute of Biomedical Technologies, Nizhny Novgorod, Russian Federation 3 Nizhny Novgorod State Medical Academy, Oncology, Nizhny Novgorod, Russian Federation 4 Institute of Applied Physics, Nano-optics and highly sensitive optical measurement, Nizhny Novgorod, Russian Federation 5 University of Toronto and University Health Network, Department of Radiation Oncology, Toronto, Canada Purpose or Objective Mucositis is a most common limiting toxicity of radio(chemo)therapy of head and neck cancer. All systems of its grading are based on visual symptoms and patient complaints; these cannot provide objective and quantifiable information. Optical coherence tomography (OCT) is a noninvasive technique for imaging biotissues with micron-scale spatial resolution and capillary-level microvascular visualization. The study objective was in

vivo monitoring of the oral mucosa during the course of radio(chemo)therapy of oropharyngeal cancer by the OCT. Material and Methods Twenty-five patients with stage I–IV of oral and pharyngeal squamous cell cancer are reported. Patient characteristics and treatment modalities are summarized in Table 1. Mucositis was scored by RTOG/EORTC scale. OCT imaging was performed twice a week from the first day of irradiation on two standard symmetric sites inside both cheeks along the centre of line connecting the secretory duct of the salivary gland and the angle of the mouth. A spectral domain OCT system (IAP RAS, Nizhny Novgorod, Russian Federation) operating at 1.3 µm central wavelength with axial resolution of ~10 µm and lateral resolution of ~15 µm was used. Optical probe was positioned on oral mucosa with gentle contact. Based on temporal speckle variations as the source of microvascular image contrast, OCT angiography images (3 mm x 3 mm) were obtained. The derived metric was vessels density that was calculated as mean number of pixels of vessels skeletons in the image. The values of reported microvascular metric throughout the course of therapy were compared to pre-RT level.

Results

The OCT microvascular images of the normal mucosa show dense and uniform microvascular networks, mostly consisting of relatively large vessels ( Fig.1a ). At doses of 4-8 Gy, images exhibited an increased vessels density ( Fig.1b ). Continued dose accumulation caused an increase in the clinical manifestations of radiation