Statistical calculation of target creation geometric limits (marj) planned by using two-dimensional and three-dimensional imaging techniques

In the study, the determination and comparison of set-up errors by twodimensional (2D) and three-dimensional (3D) Conic Beam Computed Tomography (CBCT) images in the X-rays treatment of head and neck cancer patients were performed. It is aimed to statistically investigate the adequacy of the Planned Target Volume (PTV) margin by comparing with results. In this study, the defined set-up errors by 2D and 3D-CBCT at kV energy level were compared for VMAT treatment of head and neck cancer patients. For this purpose, the acquisition of 2D and 3D-CBCT images of the kV energy level in the radiation treat ment (IGRT) processes for ten head and neck cancer patients were performed and exami ned. All VMAT treatments were done at Elekta Versa HD Linear Accelerator device. The 2D and 3D images of the patient were used by imaging system consisting of the X-ray tube and detector that mounted on the linear accelerator. Set-up errors in AP (x), RL (y) and SI (z) directions were separately determined according to x, y and z coordinate system by online correction protocol during the treatment. PTV margins were calculated for all patients using the treatment table shift values obtained from the matches with the images. Calculated margins were found to be 2.8-3.8 mm from both imaging methods. PTV margin value to be given to CTV using two-dimensional and threedimen sional images for ten head and neck patients was found to be less than 0.5 cm in RL (right-left), SI (Superior-inferior) and AP (Anterior-Posterior) directions and it is concluded that the margins given in the clinic are sufficient. However, during the total treatment process, the evaluation of the imaging radiation, the evaluation of the addi -tional radiation dose given to the patient due to kV-kV or kV-CBCT imaging procedure should be considered.