Multimodality simulation is the most accurate process available to localize, define, and reconstruct a patient´s tumor in 3 dimensions. Three dimensional radiation therapy (3DRT) as the most up to date treatment method in radiation oncology requires, that optimal target localization is achieved, especially in Intensity Modulated Radiation Therapy (IMRT). Vital to the process of virtual simulation is the imaging device with a flat table top and the RT planning software with virtual simulation option, interfaced to the precision marking system with moving lasers. A modern CT scanner can delineate target volumes and organs at risk with high precision. The capabilities of the scanner are enhanced, when a DORADOnova laser marking system is part of the scanner configuration.This laser system projects and marks the correct treatment set-up directly on the patient´s skin, eliminating the need of a conventional simulator. Precision marking enables the radiation therapist to reproduce the treatment set-up each day with a high degree of accuracy.