ESTRO 2024 - Abstract Book

S669

Clinical - Breast

ESTRO 2024

treatment plans. From this dataset we identified left-sided breast cancer patients prescribed locoregional RT with 40 Gy in 15 fractions.

All treatment plans were made based on the guidelines of the Danish Breast Cancer Group (DBCG). Patients were planned with VMAT if 3DCRT failed ensuring V95%≥95% for the breast/chestwall (CTVp_breast/chestwall), V90%≥95% for regional lymph nodes and at the same time fulfilling V17Gy≤37% for ipsilateral lung and Dmean≤4 Gy for the heart.

Deep-inspiration breath hold was used for all patients able to comply with the technique.

Extracted dose parameters include V95% and V90% (corresponding to V38Gy and V36Gy, respectively) for target coverage and V107% and V110% for hotspots. For all OAR we extract Dmean and V17Gy for ipsilateral OAR and V5Gy for contralateral lung.

Results:

We identified 38 patients treated with VMAT, and 171 patients treated with 3DCRT, where dose parameters could be extracted. Of these 119 had breast conserving surgery and 90 has mastectomy.

With VMAT planning, the target coverage for challenging anatomies was at least as good as achieved with standard tangential techniques for typical patient anatomies (figure 2, left column). For the heart, the mean dose increased on average in the challenging anatomies, but was generally below 5Gy and in most cases below 4Gy. The increase in mean heart dose was primarily due to increased low dose volumes, while high dose was significantly reduced (figure 2, middle column). Ipsilateral lung dose (figure 2, right column) was reduced slightly for both mean dose (median from 13.5Gy to 12.9Gy) and V17Gy (median from 34.6% to 32.7%).