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.