['Adjuvant left breast radiotherapy (ALBR) for breast cancer can result in significant radiation dose to the heart. Current evidence suggests a dose-response relationship between the risk of cardiac morbidity and radiation dose to cardiac volumes. This study explores the potential benefit of utilising a deep inspiration breath hold (DIBH) technique to reduce cardiac doses.', 'Thirty patients with left-sided breast cancer underwent CT-simulation scans in free breathing (FB) and DIBH. Treatment plans were generated using a hybrid intensity-modulated radiation therapy technique with simultaneous integrated boost. A dosimetric comparison was made between the two techniques for the heart, left anterior descending coronary artery (LAD), left lung and contralateral breast.', 'Compared with FB, DIBH resulted in a significant reduction in heart V30 (7.1 vs. 2.4%, P < 0.0001), mean heart dose (6.9 vs. 3.9 Gy, P < 0.001), maximum LAD planning risk volume (PRV) dose, (51.6 vs. 45.6 Gy, P = 0.0032) and the mean LAD PRV dose (31.7 vs. 21.9 Gy, P < 0.001). No significant difference was noted for lung V20, mean lung dose or mean dose to the contralateral breast. The DIBH plans demonstrated significantly larger total lung volumes (1126 vs. 2051 cc, P < 0.0001), smaller maximum heart depth (2.08 vs. 1.17 cm, P < 0.0001) and irradiated heart volume (36.9 vs. 12.1 cc, P < 0.0001).'] Do deep inspiration breath hold technique reduces heart dose from radiotherapy for left-sided breast cancer?