Radiation induced carotid stenosis is an undetected problem. Its incidence and severity has been underestimated. In this thesis, extracranial carotid arteries in nasopharyngeal carcinoma patients have been evaluated by colour doppler ultrasound examination. Post radiotherapy patients demonstrated some degree of carotid stenosis (77 percent). Up to 43.3 percent patients had moderate to severe carotid stenosis.; The radiation induced plaques also showed different sonographic characteristics when compared with ordinary atheromatous plaques. Radiation induced plaques are more diffuse and more frequently non-calcified. They also show more hypoechoic foci suggestive of instability of these plaques.; When carotid arteries were first injured, they responded with increase in intima media thickness and gradually developed into carotid stenosis. As the radiation induced vasculopathy developed over a long period of time, cerebral blood flow might be maintained by compensatory increase in contralateral carotid artery or collateral flow. Cerebral blood flow was shown to associate with the development of symptomatology.; Interestingly, despite common pathological changes, temporal lobe necrosis, another radiation induced vasculopathy was only shown to be loosely associated with extracranial carotid stenosis.; These patients do not tend to report their neurological symptoms in the routine oncology clinic follow up. Direct questioning about neurological symptoms and incorporation of auscultation of the neck in routine physical examination was recommended. Routine ultrasound surveillance is necessary to assess the carotid status. Patients older than sixty years old and with a history of radiotherapy more than ten years were good predictive factors for development of severe carotid stenosis. When limited resources make routine ultrasound surveillance impractical, screening of these high-risk patients may be more cost effective.
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