Cone beam computed tomography (CBCT) is commonly used for patient setting and pre-treatment verification in image-guided radiation therapy (IGRT). IGRT using CBCT allows visualization of soft tissue targets and critical structures prior to treatment in order visualize and verify the position. Furthermore, since CBCT imaging is used on a daily basis and multiple times per patient, could result potentially high cumulative doses to healthy tissues surrounding exposed target organs. In image-guided radiation therapy, especially for children, managing both imaging dose and positioning accuracy is crucial, due to they have an higher biological susceptibility and they are more likely to develop secondary cancer because of their longer expected lifespan.