Comparison of Cardiac Position among Left Breast Cancer Patients Treated Supine or Prone on NYU Protocol 05-181

To determine whether cardiac position and displacement impacts preferred patient positioning either prone or supine for patients with a left breast cancer. Ninety patients, 30 treated supine and 60 treated prone, enrolled on NYU 05-181 were evaluated for cardiac position relative to the chest wall in the prone and supine position using CT simulation scans. On NYU Protocol 05-181, the supine or prone field set-up which covered the index breast (PTV) and minimized the amount of heart in the treatment field was chosen for treatment. Measurements of cardiac location relative to chest wall (CW) were performed on three CT axial planes: 1) superior plane defined by the first pulmonary trunk segment inferior to the pulmonary trunk bifurcation, 2) inferior plane defined on coronal CT section by the most superior aspect of the diaphragm, and 3) middle plane defined at the mid-distance level of the superior and inferior planes. In addition, the anterior lung volume (ALV), the amount of lung volume anterior to the heart and posterior to the CW was contoured within the superior and inferior axial planes. In all 90 patients a statistically significant anterior movement of the heart (by gravity) towards the CW occurred from the supine to the prone position in each of the parameters measured, i.e. in the superior, middle and infero-lateral planes. Specifically, in the two groups mean heart to CW distance was significantly less for the patients treated prone compared to patients treated supine 2.6 cm (SD 1.3) vs. 3.4 cm (SD 0.8) at the superolateral, and 1.1 cm (SD 1.1) vs. 2.3 cm (SD 0.9) at the midlateral planes respectively (p < 0.001). Despite the fact that in the patients treated prone the cardiac location was closer to the CW than when imaged supine, after treatment planning the prone in-field cardiac volume was reduced by 12 cc (SD 21) as compared to the supine position (p < 0.001), and therefore the prone position was chosen for treatment. Moreover, the patients treated supine demonstrated a larger excursion (movement of the heart) when moving from supine to prone, compared to patients treated prone: supine mean ADV 49 cc (SD 16) vs. prone 34 cc (SD 17), (p < 0.001). Although we detected consistent anterior movement of the heart from the supine to prone position, the proximity of the heart to the chest wall did not correlate with the amount of heart volume included in the treatment field which assured PTV coverage. Other variables, like the breast and chest wall anatomy combined with the heart location relative to field borders appear to predict for optimal patient positioning.