title: Delineation of Internal Mammary Nodal Target Volumes in Breast Cancer Radiation Therapy.
abstract: The optimal clinical target volume for internal mammary (IM) node irradiation 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 to identify areas at highest risk of harboring occult disease.
  
  
  
  Patients with axial imaging of IMN disease were identified from a breast cancer registry. The IMN location was transferred onto the corresponding anatomic position on representative axial computed tomography images of a patient in the treatment position and compared with consensus group guidelines of IMN target delineation.
  
  
  
  The IMN location in 67 patients with 130 IMN metastases was mapped. The location was in the first 3 intercostal spaces in 102 of 130 nodal metastases (78%), whereas 18 of 130 IMNs (14%) were located caudal to the third intercostal space and 10 of 130 IMNs (8%) were located cranial to the first intercostal space. Of the 102 nodal metastases within the first 3 intercostal spaces, 54 (53%) were located within the Radiation Therapy Oncology Group consensus volume. Relative to the IM vessels, 19 nodal metastases (19%) were located medially with a mean distance of 2.2 mm (SD, 2.9 mm) whereas 29 (28%) were located laterally with a mean distance of 3.6 mm (SD, 2.5 mm). Ninety percent of lymph nodes within the first 3 intercostal spaces would have been encompassed within a 4-mm medial and lateral expansion on the IM vessels.
  
  
  
  In women with indications for elective IMN irradiation, a 4-mm medial and lateral expansion on the IM vessels may be appropriate. In women with known IMN involvement, cranial extension to the confluence of the IM vein with the brachiocephalic vein with or without caudal extension to the fourth or fifth interspace may be considered provided that normal tissue constraints are met.
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota.
authors.forename: Krishan R
authors.initials: KR
authors.lastname: Jethwa
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota.
authors.forename: Mohamed M
authors.initials: MM
authors.lastname: Kahila
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, Minnesota.
authors.forename: Katie N
authors.initials: KN
authors.lastname: Hunt
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota.
authors.forename: Lindsay C
authors.initials: LC
authors.lastname: Brown
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota.
authors.forename: Kimberly S
authors.initials: KS
authors.lastname: Corbin
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota.
authors.forename: Sean S
authors.initials: SS
authors.lastname: Park
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota.
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Yan
authors.affiliation: Department of Surgery, Mayo Clinic, Rochester, Minnesota.
authors.forename: Judy C
authors.initials: JC
authors.lastname: Boughey
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota. Electronic address: mutter.robert@mayo.edu.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Mutter
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008198:Lymph Nodes / Q000000981:diagnostic imaging* / Q000528:radiation effects; D008207:Lymphatic Metastasis; D000072662:Margins of Excision; D008875:Middle Aged; D020266:Radiotherapy, Conformal / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden / Q000528:radiation effects