Squamous Cell Carcinomas

Introduction
1.head and neck cancer
Around all over the world head and neck [H&N] malignant tumors are considered a major public health disorder. Head and neck cancers represent roughly about 6% of all cancers types. Two main risk factors cause this type of cancer are tobacco and alcohol, other risk factors can participate such as prolonged sun exposure, Some strains of virus, Gender, Age, Race ,Poor Oral and dental hygiene, environmental or occupational inhalants (certain chemicals, wood dust, paint fumes and inhaling asbestos ) and weakened immune system. About 90% of these tumors are Squamous cell carcinomas, So named Squamous Cell Carcinomas (HNSCC). Head and neck cancers expression is usually used to describe tumors originate from the

Radiotherapy is considered the corner stone for treating locally advanced head and neck tumors. It may be the only treatment modality for head and neck tumors (radical therapy) or it may be following surgery (adjuvant therapy) to destroy any residual malignant cells which can't be removed surgically. Regimens of radiotherapy often consist of definite number of fractions (doses) given over a set period of time. For any type of head and neck tumors, patients should be examined by dentist before beginning radiotherapy because it can cause tooth decay, damaged teeth may need to be removed. patents also should be evaluated by a speech pathologists to deal with problems resulting after radiotherapy. For tumor local control, doses up to 72 Gy (with conventional fractionation of 2Gy) can be used depending on the tumor site and stage. Doses up to 54 Gy are suitable for eradicating microscopic malignant cells followed by shrinking field techniques to deliver higher doses to Gross tumor volume (GTV) or areas with high risk. RT for (H&N) patients is considered one of the most challenging tasks in radiotherapy because this region distinguish by its complex anatomy and the planning target volume (PTV) with the convex shape containing the spinal cord (the most vital OAR at this site), has a large extension. Each development in RT technology has been performed to achieve promising balance between highly required tumor local control and sparing critical organs at risk. Despite the alteration from conventional 2D treatment planning to 3dimensional conformal planning radiation therapy (3DCRT) was considered a revolution in RT as a result of target delineation is often carried out slice by slice based on computed tomography (CT) images (which in turn presents more accurate tumor definition and dose calculation), the classic 3DCRT technique (which