A Report of Radiotherapy Setup Errors in Pelvic and Mediastinal Tumors

Abstract

Introduction: Radiation therapy as an important step in treatment of cancer which demands accuracy. Patient setup is a challenging job in the radiation therapy process. The Variation in random setup error for specific sites is different among clinics, even from one radiation therapist technologist to other in a same clinic. The purpose of this study is to investigate and report about the setup margins in the pelvic and mediastinal sites. Method &Material: 34 patients (20 males and 14 females) in the supine and prone positions (24 supine positions and 10 prone positions) were selected. Internal protocol and custom-made positioning devices were utilized. The variation of Anterior-Posterior movements (AP) in daily setup is recorded based on the vertical information which is shown on the arian 2100C/D Linear Accelerators monitor. The correlation between body type, position and treatment cases compares with the mean errors. Conclusion: The highest random error for setup is attributed to mediastinal tumor (=0.3 cm), and the highest systematic error is dedicated to cervix (=1.4 cm). The population systematic error (=1.25) is defined as the standard deviation of means of patients(Σ). In centers with lack of image-guided facilities or centers with high loaded patients the setup process should be accurate enough to limit setup error probabilities.