الفهرس 
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Abstract
Head and neck cancer (HNC) is the 6th most common cancer worldwide, with over half a million new cases each year.
Radiotherapy (RT) is one of the most common treatment modalities for cancer Radiotherapy inthe treatment of disease.
Radiation treatment can cause loss of function in normal tissues, radiation-induced toxicities in tumor-adjacent normal tissues remain the major limiting factor for the treatment. Therefor a major goal is to identify predictors for increased radiosensitivity before treatment in order to allow an individualization of radiotherapy.
8-OHdG is one of the most prevalent products of the DNA oxidation, and it is also considered to be a biomarker of DNA damage. It accumulates in DNA with age and under certain pathological conditions, e.g., associated with some types of cancer and neurodegenerative diseases.
Detection of 8-OHdG is widely used for the monitoring of exposure to genotoxic carcinogens in irradiated cells by a relatively simple and informative technique may be of a great interest in radiotherapy. It may be used to optimize conditions of irradiation and reduce the risk of secondary cancers which is unavoidably associated with radiotherapy.
This work aims to evaluate serum level of 8-OHdG in the Head and Neck cancer patients before starting radiotherapy,and after the end of radiothreapy and correlate its level with the degree ofnormal tissues toxicity related to radiotherapy.
This study includes 22 head and neck cancer patients that were treated with radiotherapy. Two blood samples were taken from each subject before radiotherapy, and at the end of radiotherapy. Each sample was divided into two parts; one of them was non-irradiated and the other was irradiated with 5 Gy. DNA Damage was detected by determination of 8-OHdGvia ELISA (enzyme-linked immunosorbent assay).
Our study shows that the percentage of acute skin reaction for head and neck cancer patients according to RTOG scale are 18%, 32%, 50% for RTOG 1, RTOG 2, and RTOG 3, respectively.Our results demonstrate that invitro irradiation at 5 Gy of whole blood from radioresistant patients induced a significant increase of extracellular levels of 8-OHdG in their serum. In contrast, the levels of extracellular 8-OHdG of radiosensitive patients were reduced.
There was no statistically significant difference in the serum levels of 8-OHdG before and after exposure to radiation to 5 Gy between male and female groups, and before and after radiotherapy.
All the radioresistant patients were non-smokers, whereas 50% of radiosensitive patients were smokers.
The Area Under the Curve (AUC) for ROC due to the effect of invitro irradiation of whole blood at 5 Gy on the levels of 8-OHdG before and after radiotherapy was 0.917 for both curves.
At a cut off value 8.9ng/ml 8-OHdG, the sensitivity was 100% and specificity was 100% before radiotherapy.At a cut off value 10.8 ng/ml 8-OHdG, the sensitivity was 100% and specificity was 100% after radiotherapy
Detection of 8-OHdG in irradiated whole blood may be used as a predictive radiosensitive marker in head and neck cancer patients.