Background: Despite of the use of tangential beam directions during the irradiation of mammary carcinomas, a dose reduction of the heart cannot always be achieved. This is decivise for the increased risk of heart diseases and the associated mortality. Especially affected is the cardiac apex. However, by using respiratory gated treatment techniques, like the deep inspiration breath-hold (DIBH), a dose sparing of this area can be reached.
Material and Methods: The Elekta ABC system was used to control the respiratory stop of early staged breast cancer patients. The treatment planning was implemented by a 3D and VMAT technique. The focus was the optimization of irradiation plans and the evaluation of the respective dose exposure to the heart, the left ventricle and the left anterior descending coronary artery (LAD artery). A planning concept of 28 x 2,25 Gy in the SIB and 28 x 1,8 Gy in the left breast was used.
Results: The results showed that a dose reduction of 30-40% in mean and maximal in all structures is possible by using the VMAT technique in combination with the ABC system. In the case of 3D irradiation planning, a substantial relief can only be seen at the mean dose exposure of approximately 50%. Also, only a maximum dose reduction of 13% could be achieved.
Conclusion: The mean dose reduction was mainly achieved by the increased distance between the heart and the thorax wall. The maximum dose was reduced by the volumentric optimization algortihm of the VMAT and the resulting steeper dose fall-off at the inner thoracic wall. Due to the lack of this optimization and thus the greater dose drop, the maximum dose of the 3D plans could only reduced by 13%.