Paper Title
INVESTIGATION OF THE EFFECT OF METAL HIP PROSTHESIS ON DOSE DISTRIBUTION IN RADIOTHERAPY FOR 18MV PHOTON BEAM USING TLD

Abstract
Abstract - In RT, beam planning and dose evaluations are also made in the treatment planning system (TPS). Hip prostheses located close to the target volume cause heterogeneous dose distribution and adversely affect the desired dose distribution. In the study, a Co-Cr-Mo (Cobalt-Chromium-Molybdenum) alloy hip prosthesis was placed in a special cylinder phantom with a density close to human tissue with a three-dimensional printer and exposed to 18 MV photon beam. In vivo dose distributions were measured by inserting a thermoluminescent dosimeter (TLD) and compared with results from AAA. The stem size and stem length of the prosthesis were 12 mm and 150 mm, respectively. The prosthesis was divided into 3 parts according to their thickness, the thick part (part1), the middle part (part2) and the thin part (part3), respectively. Point dose measurements on the X and Y axes within the phantom were obtained from the AAA algorithm and TLDs. A total of 300 MU beam planes were created, with 150 MU for each of the gantry 0 and 180 angles. The aircraft was irradiated using 18 MV photon energy with 2 different beam fields. It was observed that the thickness of the metal affected the surface dose of the prosthesis. Accordingly, the difference between AAA and TLD doses on the prosthesis surface was 3.64%, 1.63% and 0.64% for part1, part2 and part3, respectively. The difference in dose distribution of AAA and TLD at 1 cm from the prosthesis was 5.41%, 3.61%, and 5.13% for the thick, medium, and thin sections, respectively. It was observed that the uncertainty of the AAA algorithms increased as the density and diameter of the hip replacement increased. Therefore, in the treatment of patients with hip replacement with radiation, it should be considered that the prosthesis may affect the treatment. Keywords - CoCrMo Alloy, Hip Prosthesis, Radiotherapy, Thermoluminescent Dosimeter