Factors Affecting Contralateral Breast Dose in Radiation Treatment of Breast Cancer

Materials/Methods: Recurrent or advanced breast cancer patients with contrasted CT images to cover the whole regional nodes at the time of recurrence or advanced disease staging prior to systemic therapy were eligible. The regional lymph nodes were categorized into 8 anatomical substructures: medial and lateral-supraclavicular(Sc-M, Sc-L); axilla (ALN)-I,II,III; infraclavicular (Ic); Rotter’s nodes (RN) and internal mammary nodes (IMN). Frequency of involvement and anatomical characteristics of the involved nodes on CT images were analyzed. Results: A total of 97 regional recurrent pts and 14 advanced breast cancer pts with eligible images from July 2003 to January 2009 entered current study. Within the 111 pts, 199 anatomical substructures of involved nodes were identified. The frequency of involvement includes: Sc-M: 33 (16.6%), Sc-L:21 (10.6%), ALN-I: 30 (15.1%), ALN-II: 25 (12.6%), ALN-III and Ic: 35 (17.6%), RN: 27 (13.6%), IMN: 28 (14.1%). In pts received prior axillary dissection, 67.0% (114/170) had recurrent nodes cranial to the axillary vein. With IMN involvement, 26/28 had nodes within the first 3 intercostal spaces. The average distance between the center of involved IMN and midline is 29.38 ± 6.7 mm. The average distance between the center of involved IMN and internal mammary vessels (IMV) are 6.19 ± 5.73 mm in lateral and 5.73 ± 4.56 mm in depth. The average maximum depth of involved Sc nodes is 53.19 ± 21.68 mm. Conclusions: Identification of involved regional nodes in recurrent and advanced breast cancer is beneficial for better understanding the distribution of risk area. The lymphatic structures observed in our series confirm that current target definition of regional nodes is consistent with the potential risk of regional lymphatic spread. Sc and axillary nodes cranial to the axillary vein should be considered the primary risk target as it accounts for 2/3 of the recurrent nodes. The anatomical relationship of IMN and IMV supports the use of IMV as reference in IMN delineation and 7-10 mm from the center of IMV should be regarded as adequate definition of CTV to IMN. Conventional field design is unlikely to provide sufficient dose to the entire risk region. Individual treatment planning would become feasible with increasing knowledge of natural risk of nodal involvement. Author Disclosure: J. Chen, None; C. Zhu, None; J. Chen, None; G. Cai, None; J. Ma, None; X. Guo, None.