فهرست مطالب ثریا غلامی

Beam-hardening artifacts in CT image set of patient with a hip prosthesis cause difference between dose distributions resulted by treatment planning system (TPS) algorithms and actual dose distribution in patient body. In this study, dose distributions of TPS algorithms were compared with the results of Monte Carlo simulations of Titanium and Steal as a hip prosthesis for different photon energy.
Siemens Primus linear accelerator was modeled using the MCNPX code for 6MV and 15MV energy mode. Dose reduction due to Titanium and Steal were calculated by different algorithms of Isogray TPS and compared with the results of Monte Carlo simulations of Titanium and Steal. The accuracy of the algorithms for different depth and energy was evaluated.
In 6MV energy, for Titanium, there was 12.9%, 12.6% and 10.7% and for Steal, there was 14.3%, 14.1% and 12.1% differences between simulation results and TPS algorithms included Superposition, Collapsed cone and FFT Convolution respectively. In 15MV energy, for Titanium, there was 15%, 15.6% and 13.3% and for Steal, there was 21.7%, 22.3% and 20.1% differences between simulation results and TPS algorithms included Superposition, Collapsed cone and FFT Convolution respectively.
There was significant dose reduction due to hip prosthesis whereas the TPS algorithms do not have ability to predict the dose reduction accurately. Thus, use of Monte Carlo based algorithms recommend for dose calculation in patient with high density prosthesis.

The difference of calculated dose by treatment planning system (TPS) and real dose distribution in patient body is related to calculating algorithms of TPS, and this difference is more evident in heterogeneous tissues like lung. In this study dose distribution was calculated by two algorithms of Isogray TPS and compared to dose distribution calculated by Monte Carlo simulation in water and lung.
Subjects and In this study, the percentage depth dose (PDD) curves resulting from different algorithms of Isogray TPS were compared by data from simulation in homogeneous water tissue. The difference between dose distribution calculated by Isogray TPS algorithm and CT2MCNP program were obtained and accuracy of mentioned algorithm were evaluated in lung.
The difference between simulation results and results of TPS algorithms including collapsed cone, Fast Fourier Transform (FFT) convolution and superposition in heterogeneous lung tissue was calculated 5%, 6% and 7%, respectively. In the maximum dose, The obtained difference was 7 % with the same algorithms. no significant differences in the water between simulation results and results of TPS algorithms were observed. and the difference was obtained less than 1%.
In clinical treatment, there was significant difference in dose calculation by TPS algorithm in heterogeneous lung tissue. But this difference was negligible in homogeneous tissues.