Assessment of cardiac exposure in left-tangential breast irradiation

To assess the value of treatment-planning related parameters namely, the breast volume; the distance of the inferior field border to diaphragm; and the cardiothoracic ratio for left-tangential breast irradiation.

Treatment plans of 27 consecutively left-sided breast cancer patients after breast conserving surgery were evaluated for several parameters concerning heart-irradiation. We measured the heart distance respective to the cardiothoracic ratio and the distance of the inferior field border to diaphragm, as well as the breast volume in correlation with the irradiated heart volume.

The mean heart and left breast volumes were 504 cm(3) and 672.8 cm(3), respectively. The mean heart diameter was 13.4 cm; the mean cardiothoracic ratio 0.51 and the mean distance of the inferior field border to diaphragm was 1.4 cm. Cardiothoracic ratio (p=0.01), breast volume (p=0.0002), distance of the inferior field border to diaphragm (p=0.02) and central lung distance (p=0.02) were significantly correlated with the measured heart distance. A significant correlation was also found between cardiothoracic ratio, breast volume and distance of the inferior field border to diaphragm with the irradiated heart volume measured by V10, V20 and V40.

The verification of parameters like cardiothoracic ratio, distance of the inferior field border to diaphragm and breast volume in left-sided breast cancer patients may help in determining which patients could benefit from more complex planning techniques such as intensity-modulated radiotherapy to reduced risk of late cardiac injury.