Isolated Locoregional Recurrence Patterns of Breast Cancer After Mastectomy in the Era of Multimodality Therapy

Abstract

Purpose/Objective(s): To identify the location and boundary of metastatic supraclavicular nodes (SCN) in breast cancer patients and evaluate the coverage of RTOG atlas using diagnostic computed tomography (CT) maps of SCN. Materials/Methods: The diagnostic CT images of 55 patients with ipsilateral SCN were reviewed. Due to different body positions during diagnostic CT, a standard sim-CT of one breast cancer patient was selected to contour clinical target volume (CTV) of supraclavicular nodal region per RTOG breast atlas. Locations of SCN of each patient were contoured on this same sim-CT based on surrounding anatomical references. Sizes of nodes and distances to nearby structures were proportionally reproduced during contouring to generate map1. A map2 with a 5 mm spot representing the epicenter of each node was built to reduce volume effects. Locations and coverage of SCN by CTV-RTOG were analyzed. Results: Among those 55 patients, 29 (52.7%) had left-sided and 26 (47.3%) had right-sided primary lesions, 34 (61.8%) had SCN concurrent or after distant metastasis (DM), and 15 (27.3%) had SCN without DM. Fifty (90.9%) patients had medial SCN, and 40 (72.7%) had lateral SCN involvement. Thirty-six (65.5%) patients had SCN located in the jugularsubclavian venous confluence. In map1, CTV-RTOG only adequately covered the SCN in 6 (10.9%) patients, with SCN extending outside the anterior, medial, posterior, and lateral border of CTV-RTOG in 2 (3.6%), 4 (7.2%), 46 (83.6%), and 45 (81.8%) patients. In map2, CTV-RTOG adequately covered the SCN epicenters in 13 (23.6%) patients, with SCN outside the anterior, medial, posterior, and lateral border of CTV-RTOG in 0 (0%), 1 (1.8%), 36 (65.5%), and 39 (70.9%) patients, respectively. There were no significant differences in locations or CTV-RTOG coverage of SCN between patients with left-sided and right-sided SCN, or between patients with and without DM. Given 37 (67.3%) and 23 (41.8%) patients harboring SCN lateral and posterior to scalene muscles, in order to cover over 85% of the SCN, the posterior border of CTV should extend to the lateral surface of levator scapulae and anterior surface of trapezius muscles, and the subclavian vessels should be included before they go beyond the interior border of pectoralis minor. The lateral border should extend to the lateral border of trapezius muscle. Conclusions: Metastatic SCN in breast cancer frequently involves the medial followed by the lateral SCN region and jugular-subclavian venous confluence. RTOG breast atlas is insufficient for coverage of SCN, especially in the lateral and posterior directions. A larger and tailored volume should be defined for optimal field design in prophylactic supraclavicular region irradiation. Author Disclosure: H. Jing: None. S. Wang: None. J. Li: None. Y. Li: None. M. Xue: None. Z. Yu: None.