Yan, E

Abstract Purpose/Objectives: The optimal clinical target volume (CTV) for internal mammary node irradiation (IMNI) is uncertain in an era of increasingly conformal volume-based treatment planning for breast cancer. We mapped the location of gross internal mammary lymph node (IMN) metastases in order to identify areas at highest risk for harboring occult disease. Methods and Materials: Patients with axial imaging of IMN disease, including fluorodeoxyglucose F-18 (FDG18) positron emission tomography (PET-CT) and magnetic resonance imaging (MRI), were identified from a breast cancer registry. The IMN location was transferred by a radiation oncologist and breast radiologist onto the corresponding anatomic position on representative axial CT images of a patient in the treatment position. Distribution of lymph nodes, and their location was compared with consensus group guidelines of IMN target delineation. Results: Sixty-seven patients with 130 IMN metastases were mapped. The location was in the first three intercostal spaces in 102 of 130 (78%) nodal metastases. Eighteen of 130 (14%) IMN were located caudal to the third intercostal space, while 10 of 130 (8%) IMN were located cranial to the first intercostal space, including 3 patients with isolated IMN metastases at that location in the absence of distant disease. Of the 102 nodal metastases within the first three intercostal spaces, 54 (53%) were located within the RTOG consensus volume. Relative to the internal mammary (IM) vessels, 19 (19%) nodal metastases were located medially with a mean distance of 2.2 mm (SD 2.9 mm), while 29 (28%) were located laterally with a mean distance of 3.6 mm (SD 2.5 mm). Ninety and ninety-five percent of lymph nodes within the first three intercostal spaces would have been encompassed within a 4 mm and 6 mm medial and lateral expansion on the IM vessels, respectively. Conclusions: For women with indications for elective IMNI, a 4 mm medial and lateral expansion on the IM vessels within the first 3 intercostal spaces may be appropriate. In women with known IMN involvement, cranial extension to the confluence of the IM vein with the brachiocephalic vein +/- caudal extension to the 4th or 5th interspace with a 6 mm medial and lateral expansion may be considered, provided that normal tissue constraints are met. Citation Format: Jethwa KR, Kahila MM, Hunt KN, Brown LC, Corbin KS, Park SS, Yan ES, Boughey JC, Mutter RW. Delineation of internal mammary nodal target volumes in breast cancer radiotherapy [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-10-09.

Abstract Lymphedema (LE) is a common complication of cancer treatment, and has been identified as the number one issue by breast cancer survivors with incidence as high as 70%. Given the long-term survivorship of these women, LE is a widely prevalent condition. Irradiation of axillary and supraclavicular lymph nodes increases a patient's risk of LE onset and progression by as much as 2-fold. It is anticipated that a more individualized approach to post-surgical irradiation of breast cancer patients may reduce radiation-induced lymph node (LN) damage without sacrificing control rates, although it is noted that a definitive radiation exposure threshold below which LNs physiological integrity will be preserved is currently lacking. To identify the locations of the small, non-pathological but physiologically relevant LNs which drain the arm after breast cancer surgery and incorporate them into radiation planning, filtered 99mTc sulfur colloid (TcSC) was administered and a SPECT-CT scan was acquired for 22 patients immobilized in the treatment position. These images were registered with the Radiation Oncology planning CT scan, and draining LN were contoured automatically using a threshold of 50% maximum intensity. Two treatment plans were generated for each patient, one per routine clinical practice (STD) and the other (MOD) with treatment fields modified to minimize dose to the LNs visible on SPECT/CT images while ensuringthat ≥50Gy or biologic equivalent is delivered to target tissues. 53 draining LN were identified, 54% of which were inside the STD plan fields but could be blocked in the MOD plan fields. 62% of LN in the STD plans vs. 17% in the MOD plans receiving a mean of ≥10Gy, and 27% in the STD plans vs. 6% in the MOD plans receiving a mean of ≥40Gy. Patient-specific LN dose reduction can be achieved through integration of SPECT/CT images into the radiation planning process. These patients will be followed for the development of LE, to estimate an exposure threshold below which LN preservation is assured. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-11-20.