Cardiac dose evaluation for 3Dimensional conformal partial breast irradiation compared with whole breast irradiation

Abstract

Purpose: To compare the radiation dose to normal cardiac tissue for 3-dimensional (3-D) conformal external beam partial breast irradiation (PBI) and standard whole breast irradiation (WBI) and examine the effect of tumor bed location.Methods: For 14 patients with left breast tumors randomized on the National Surgical Adjuvant Breast and Bowel Project B-39 protocol, computer-generated radiotherapy treatment plans were devised for WBI and PBI. Tumor bed location was designated according to whether more than 50% of the excision cavity was medial or lateral to the nipple line. The plans were then compared using dosimetric parameters below.Results: Of 14 patients, 8 had lateral tumor beds, and 6 had medial tumor beds. The volume of heart receiving 2.5, 5, 10, and 20 Gy was 2.4%, 1.3%, 0.6%, and 0.1%, respectively, for the lateral tumor beds and 13.2%, 8.2%, 2.3%, and 0.4%, respectively, for the medial tumor beds. Mean doses to 5% of the heart volume (D5) for lateral PBI, medial PBI, and WBI were 1.67 Gy, 5.10 Gy, and 5.69 Gy, respectively. Mean heart doses for lateral PBI, medial PBI, and WBI were 0.48 Gy, 1.31 Gy, and 1.68 Gy, respectively. Conclusion: Both 3-D conformal PBI and standard WBI can be delivered with relatively low doses to the heart. For patients with lateralized tumor beds, PBI offers significant sparing of cardiac tissue compared with WBI. Patients with medial lesions have relatively similar heart dosimetry with PBI and WBI.