The lungs are a primary dose limiting organ in high dose total body irradiation (TBI). Accurate prediction of lung dose can dictate treatment success by preventing pulmonary toxicity. Normal treatment planning consists of basic hand calculations and in vivo dosimetry. The use of a treatment planning system (TPS) is an unverified method at the extended treatment distance required by TBI. Our aim is to analyze the Eclipse TPS as a viable method to determine required monitor units (MU) to meet a prescription and estimate dose to the lungs during blocked treatment fractions.