ESTRO 37 Abstract book

ESTRO 37

S587

5 University of Toronto and University Health Network, Department of Radiation Oncology, Toronto, Canada

Results

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.

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 reaction, as also seen by the OCT angiography maps ( Fig.1c,e,g ); after start of anti-mucositis therapy the microvascular increase tended to slow down ( Fig.1g,h ). These visual conclusions were confirmed by quantitative processing of the OCT images. Statistically significant changes of microvascular parameters were detected when grade one, two and three mucositis developed ( Fig.1i ). In addition to these general trends based on the analysis of all examined patients, the real potential of OCT microvascular monitoring was evident in patients who received IMRT. OCT metric corresponded to different dose accumulated in the PTV, dependent on tumor location and treatment modality. Conclusion The study showed that OCT angiographic monitoring can be used for objective evaluation of radiation induced microvascular changes, thus ‘shedding light’ on early functional and structural radiation toxicity. This may potentially play a role in the design and efficacy evaluation of treatment and prophylaxis modalities of mucositis and in the implementation of adaptive radiotherapy protocols.

Poster: Radiobiology track: Radiobiology of proton and heavy ions

PO-1045 Photon, proton and C12 irradiation influences maturation and functionality of dendritic cells L. König 1 , A. Hommertgen 1 , D. Bernhardt 1 , J. Hörner- Rieber 1 , P. Huber 1 , K. Herfarth 1 , J. Debus 1 , S. Rieken 1 1 University Hospital Heidelberg, Department of Radiation Oncology, Heidelberg, Germany