Purpose: Total body radiation (TBI) has been used for many years as a pre‐conditioning agent before bone marrow transplantation. Many side effects still plague its use. To assess the feasibility of using Helical Tomotherapy, we investigated various parameters and treatment techniques. Method and Materials: We studied variations in pitch, field width, and modulation on total body and total marrow helical tomotherapy treatments. We varied these parameters to provide a uniform dose along with a treatment times similar to conventional TBI (15–30 min.). We also investigated using limited total body mega‐voltage CT (MVCT) scanning rather than total body MVCT scanning to shorten the time per treatment fraction. Thermoluminescent detectors (TLDs) were placed inside a Rando phantom and we measured dose at seven anatomical sites including the lungs. Whole body MVCT and limited MVCT (head, chest, and pelvis) scanning were used for 3‐D set up verification. Results: TBI simulation showed homogeneous dose coverage to the whole body. Doses to the sensitive organs were reduced by 35–70 % of the target dose. In the TMI study, dose was mainly conformal to the bone marrow only. TBI and TMI treatment delivery time was reduced (by 50%) by increasing the field width from 2.5 cm to 5.0 cm in the inferior‐superior direction. TLD measurements on Rando showed accurate dose delivery to the target and critical organs. A limited MVCT reduced the target localization time significantly compared to whole body MVCT. Conclusion: This study showed that Helical Tomotherapy can deliver uniform dose to the total body and total marrow by a judicious selection of pitch, modulation, and field size. A limited MVCT also can be used in place of whole body MVCT. Details of this investigation will be presented. Conflict of Interest: The authors associated with TomoTherapy Inc. have a financial interest in that company.