ESTRO 2021 Abstract Book

S18

ESTRO 2021

Figure 1. Planning CTs with anatomic changes according to the white arrows. 1) As scanned 2) Anterior expansion 3) Lateral expansion. Results In figure 2, the target coverage and mean dose to OAR are compared. The VMAT plans have slightly higher PTVp_breast V47.5Gy compared to the 3D-CRT plans. However, there is also an increase in V52.5Gy. For the IMN, V45Gy is increased by 9%-points. The dose to OAR is distributed differently. While the median mean heart dose remains roughly unchanged, the relative volumes receiving 20 and 40 Gy are reduced. The mean ipsilateral lung dose is reduced. The contralateral lung and breast receive higher average dose due to a larger volume with 5-15Gy dose. Considering the target coverage, the 3D-CRT plans are generally robust to the simulated anatomical changes. Most notable change is the median V45Gy for IMN, which drops 5%-points with anterior expansion. The VMAT plans are in general more robust, i.e. maintains higher dose coverage, and in no cases inferior.