ESTRO 2024 - Abstract Book

S494

Clinical - Breast

ESTRO 2024

685

Digital Poster

Incidental dose distribution to contralateral internal mammary nodes in breast cancer patients

Sophie Therese Behzadi 1 , Rebecca Moser 1 , Sophia Kiesl 1 , Stephanie Elisabeth Combs 1,2 , Kai Joachim Borm 1

1 Technical University Munich, Radiation Oncology, Munich, Germany. 2 Helmholtz Zentrum München, Institute for Radiation Medicine, Munich, Germany

Purpose/Objective:

Previous studies revealed lymphatic drainage to the contralateral internal mammary chain in up to 17% of a healthy cohort and bilateral internal mammary node (IMN) metastasis in up to 29% of breast cancer patients [1-4] . Nevertheless, this part of the lymphatic drainage pathway is usually not taken into consideration during adjuvant radiotherapy. This study aims to evaluate the incidental dose coverage of the contralateral IMN in patients with advanced breast cancer.

Material/Methods:

120 treatment plans for 40 patients with left-sided, node positive breast cancer were calculated with and without inclusion of internal mammary region (IMNI) in free breathing (FB) and deep inspiration breath hold (DIBH). Contralateral IMN (1-5th intercostal space) and supraclavicular CTVs were delineated according to ESTRO consensus guideline [5] with a 5 mm PTV margin.

We analyzed mean doses of contralateral IMN and supraclavicular target volumes (CTV and PTV). Moreover, we evaluated V30Gy of the contralateral IMN CTV as well as mean doses of the organs at risk.

Results:

The mean incidental dose (Dmean) to the contralateral IMN CTV of all treatment plans was 13.0 Gy (2.2 to 25.6 Gy). The Dmean for contralateral IMN PTV was 13.3 Gy (2.4 to 25.6 Gy). The mean dose distribution of the first to the fifth intercostal spaces were 14.5 Gy, 12.8 Gy, 13.1 Gy, 12.5 and 8.0 Gy respectively. Dmean for supraclavicular CTV and PTV was 14.1 Gy. For radiation plans with inclusion of ipsilateral IMNI (n=80) the Dmean of the contralateral IMN CTV was significantly higher than in those without ipsilateral IMNI (n=40; 14.3 Gy vs. 9.6 Gy; p=.0001). In only 9 cases the maximum dose in the contralateral IMN exceeded 30 Gy with a median V30 of 0.2 cm3.