ABSTRACT: Radiation therapy is an area of ​​medicine that treats malignant and benign lesions. This treatment modality is performed with ionizing radiation, such as electrons, x-rays and gamma rays with function of delivering the maximum doses to lesion, minimally affecting healthy tissues. This article presents the importance of using immobilizers during radiotherapy treatment, the text is based on a bibliographic review of books and articles in the radiotherapy area. The transmission of some materials used for making accessories in radiotherapy were analyzed. Among the analyzed materials, carbon fiber presented 97%, wood 96% and acrylic 92% transmission. Therefore, carbon fiber proved to be the best material for making these accessories and, as an alternative, wood presented similar and acceptable results.