The following steps are typically required as part of conformal radiation therapy: patient positioning and fixation, registration of a three-dimensional model of the patient’s anatomy, calculation of a treatment plan, simulation, and the irradiation at the treatment machines. The intention of the simulation process is to define the position and the shape of radiation ports and to mark them or their surrogates on the patient’s skin or their fixation devices before therapeutic radiation is applied. It also serves as the last check of the treatment plan. In most cases an isocentrically mounted fluoroscopic x-ray unit called “simulator” is used for this purpose. This method is called “conventional simulation” in this book. The virtual simulation process, which is the topic of this book is a sequence of working steps and methods for quality assurance with the intent of simplifying or replacing the conventional simulation process. It is also the aim of the virtual simulation process to improve the radiation delivery precision. This chapter describes the virtual simulation process with specific examples using a laser projection device from the company LAP (“Dorado CT-4”), a CT scanner from Siemens (“Somatom Emotion”), and the treatment planning system “XiO” from Computerized Medical Systems (CMS). The necessary working steps are described and compared with the conventional simulation process. As an example virtual simulation was performed for patients who had a tumour in pelvic region or in the head. The results were compared directly with conventional simulation by comparing the positions of the ports drawn at the CT scanner and the coordinates determined during conventional simulation.weiterlesen