Dose and organ displacement comparisons with breast conservative radiotherapy using abdominal and thoracic deep‐inspiration breath‐holds: A comparative dosimetric study

Deep‐inspiration breath‐hold (DIBH) reduces the radiation dose to the heart and lungs during breast radiotherapy in cancer. However, there is not enough discussion about suitable breathing methods for DIBH. Therefore, we investigated the radiation doses and organ and body surface displacement in abdominal DIBH (A‐DIBH) and thoracic DIBH (T‐DIBH). Free‐breathing, A‐DIBH, and T‐DIBH computed tomography images of 100 patients were used. After contouring the targets, heart, and lungs, radiotherapy plans were created. We investigated the heart and lung doses, the associations between the heart and left lung displacements, and the thorax and abdominal surface displacements. No significant differences were observed in the target dose indices. However, the heart and lung doses were significantly lower in A‐DIBH than in T‐DIBH for all the indices; the mean heart and lung doses were 1.69 and 3.48 Gy, and 1.91 and 3.55 Gy in A‐DIBH and T‐DIBH, respectively. The inferior displacement of the heart and the left lung was more significant in A‐DIBH. Therefore, inferior expansion of the heart and lungs may be responsible for the respective dose reductions. The abdominal surface displaced more than the thoracic surface in both A‐DIBH and T‐DIBH, and thoracic surface displacement was greater in T‐DIBH than in A‐DIBH. Moreover, A‐DIBH can be identified because abdominal surface displacement was greater in A‐DIBH than in T‐DIBH. In conclusion, A‐DIBH and T‐DIBH could be distinguished by comparing the abdominal and thoracic surfaces of A‐DIBH and T‐DIBH, thereby ensuring the implementation of A‐DIBH and reducing the heart and lung doses.