Clinical Implementation of a Real-Time Electromagnetic Localization System: Accuracy, Motion and Margin Analysis for IMRT and IMAT Treatments

Accurate delivery of external beam radiation therapy relies on localization of the treatment target. For this work, the accuracy of an electromagnetic localization system (ELS) was first verified. Next, prostate deformations and rotations occurring throughout therapy were analyzed. Motion studies were also conducted to investigate the use of the ELS during intensity modulated arc therapy (IMAT) for prostate cancer. Lastly, appropriate margins were determined and new plans utilizing smaller margins were tested for two patients who exhibited large transponder displacements. Electromagnetic alignments were accurate to within 1mm as compared to x-ray imaging. All patients fell within the default geometric residual limit (2mm) and most fell within the default rotation limit (10°). The ELS appeared to be suitable for use during IMAT with a 5mm margin. A 3mm margin was tested and was adequate when the main displacements were translational shifts; however, it was not adequate when large rotational displacements occurred.