The accuracy of calculation using radiation treatment planning system with titanium in a human body

A radiation treatment planning, which was calculated using Radiation Treatment Planning Systems (RTPS) has been unsuccessful in the correct calculation of dose perturbations for high-density substances. High-density metal objects such as prosthetic dental implants, metal hip prosthesis, and others are implanted occasionally into human bodies. In this work, the dose distributions inside a tough water phantom with titanium irradiated by 4 MV and 10 MV photon beams for a 5 x 5 cm²field size were evaluated. Dose distributions were measured using Gafchromic Film RT-QA and calculated by Monte Carlo (MC) simulation or RTPS. By these evaluations, we investigated the accuracy of the calculation using RTPS for the existence of titanium. Depth-dose profiles obtained using the film and the MC simulation agreed within · 5 %. The rate of changes (RC) between the MC simulations and the RTPS calculations were -13.2 % (4 MV) or -17.2 % (10 MV) in front of titanium, and 15.8 % (4 MV) or 3.9 % (10 MV) at behind of titanium (shown in Table 1), where RC (%) = ((D_xio - D_EGS) / D_EGS) x 100, D is relative dose. For the depth deeper than 7 cm, the results show no much difference.