Although there were reports on the breath‐hold motion using various systems, 15 , 16 based on our knowledge, no one has reported the corresponding dosimetric effect. We modified our in‐house treatment planning system (TPS) so that it can process the actual patient motion information and calculate the dosimetric variation due to the motion. We describe how the calculation was done in the Materials and Methods section below. The purpose of this study was to answer a clinical question: How much dosimetric variation the breath‐hold motion might generate compared to the plan?