Page 99 - Effects of radiotherapy and hyperbaric oxygen therapy on oral microcirculation Renee Helmers

Late radiation-induced oral microvascular changes
INTRODUCTION
Irradiation of malignancies in the anatomically complex head and neck (HN) region inevitably results in collateral damage to vital tissues.13,32 Vascular damage in the oral mucosa is a late sequela following acute mucosal injury. Mucositis develops in 80% of patients during the course of curative HN irradiation and manifests as atrophy of epithelial cells and inflammatory infiltrates.26,32 Subsequent release of vasoactive cytokines results in fibrin leakage into surrounding tissues followed by vascular lumen blockage that can ultimately reduce tissue vascular perfusion and regional hypoxia.32 Late irradiation sequelae associated with irradiation dosages of 50-65 Gy 6 can emerge several months after completing RT and can lead to problems with mastication and speech (due to trismus and/or xerostomia), atrophy and fibrosis with ulceration of the oral mucosa, and in some advanced cases as osteoradionecrosis (ORN) of the jaw.6,18,27
Late irradiation side effects vary in severity and pathology among patients.
As severity of late sequelae associated with RT is not proven to correlate
with the degree of acute effects,4,23,34 it is difficult to predict the course of 5 late radiation damage. Most tissues do not reveal late side effects clinically
before a stage of severe tissue breakdown becomes apparent in the form of
soft tissue necrosis or ORN. Understanding late irradiation pathophysiology
in the microcirculation can provide a way of subclinical diagnostics to bring
to light clinically relevant information on early onset of side effects and their
severity. Tissue inspection and monitoring provides an opportunity for planning
ahead strategies to improve patient quality of life by preventing progression
of pathology. Hyperbaric oxygen is an example of such a strategy that could
potentially improve tissue resistance to injury and maintenance of health by
reducing avascularity.3,11,21,27
To date several reports on vascular irradiation were published using different techniques. Early in the 1970s studies based on histology and intravital microscopy were conducted, describing degeneration of capillaries after irradiation as telangiectasia and microaneurysms.23 Transcutaneous oxygen measurements and laser Doppler flowmetry (LDF) were each used to assess microcirculation functionally in irradiated skin and oral mucosa but failed to yield consistency in results.10,12,24,28,29 Direct observation of angioarchitecture and morphology in irradiated tissue can provide additional evidence-based
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