Prone Positioning Causes the Heart To Be Displaced Anteriorly Within the Thorax: Implications for Breast Cancer Treatment

Abstract

Prone positioning has been suggested as an alternative to the conventional supine position for patients receiving breast radiotherapy, but few data exist on how this may alter heart location. We herein quantitatively compare the intrathoracic location of the heart in the prone and supine positions in patients treated for breast cancer. In 16 patients treated with tangent photons for breast cancer, the computed tomography planning images (obtained in the supine position) and diagnostic magnetic resonance images (obtained in the prone position) were studied. For each case, the distance between the anterior pericardium and the anterior chest wall was measured at nine specific points; three points at each of three axial levels. The differences in the measurements between the prone and supine positions were compared with the Wilcoxon signed-rank test. There is a systematic displacement of the lateral and superior aspect of the heart closer to the chest wall in the prone vs. supine position (mean displacement 19 mm (95% confidence interval 13.7-25.1 mm, p < 0.001); the medial and inferior aspects remain fixed. There was also a reduction in volume of lung interposed between the heart and chest wall when prone (mean decrease of 22 mL, p < 0.001 for difference). The superior and lateral aspects of the heart typically move anteriorly during prone positioning compared with the supine position. This may have negative consequences in situations in which the high-risk target tissues include the chest wall or deep breast.