Total body irradiation (TBI)is one important part in the conditioning for bone marrow and hematopoetic stem cell transplantation. Doses up to 12 Gy are delivered in hyperfractioned regime. TBI performed with helical Tomotherapy is an alternative to conventional techniques to deliver dose in exended target volumes with the possibility of simultanous dose sparing to organs at risk (OAR). Due to feared radiation side effects (i.e. intestitual pneumonitis) in this study we focused on maximum dose reduction to the lungs using helical Tomotherapy. This planning study demonstrates that total body irradiation with helical tomotherapy offers an excellent opportunity of highly conformal and homogenous dose delivery in extensive target volumes. Compromise in PTV dose might only occur in patients with high BMI. All predefined constraints are reachable in an acceptable planning time. To our knowledge we showed for the first time, that total body irradiation with a hyperfractionated total dose of 12 Gy can be delivered simultaneously to maximum lung tissue sparing without any compromise in the dose of the target volume.