[Evaluation of setup error and adequate setup margins in patients with prostate cancer treated by IMRT and fixed in the prone position using a set of immobilization devices].

PURPOSE Positional reproducibility in patients with prostate cancer fixed in the prone position with a set of immobilization devices for external-beam intensity-modulated radiation therapy (IMRT) was evaluated. In addition, the adequacy of our positional error reduction strategy and current planning target volume (PTV) margins was also evaluated. RESULTS Systematic error was corrected by the positional correction that we executed at the first stage of irradiation. The setup margin that we had calculated was 1.1 mm in the L-R direction, 1.3 mm in the A-P direction, and 2.7 mm in the C-C direction. CONCLUSION We determined that the effectiveness of the method of correcting the error margin and the setup accuracy of the fixed method were well maintained.