title: Evaluation of axillary dose coverage following whole breast radiotherapy: variation with the breast volume and shape.
abstract: OBJECTIVE
  To evaluate the axillary dose coverage in patients treated with tridimensional whole breast radiotherapy (3D-WBRT), according to the breast volume and shape in treatment position.
  
  
  BACKGROUND
  Several studies have demonstrated an insufficient dose contribution to the axillary levels, using 3D-WBRT, remaining unclear whether the breast volume and shape can influence it.
  
  
  METHODS
  We retrospectively delineated the axillary levels on planning CT-images of 100 patients, treated with 3D-WBRT along 2012 in our institution. To estimate the shape we established an anatomic CT-based interval, defined as the Thoracic Extent (TE). The breast volume matched its CTV. Mean dose levels and V95 (volume receiving at least 95% of the prescribed dose) were evaluated.
  
  
  RESULTS
  Mean axillary level I (A1), II (A2) and III (A3) volume was 56.1 cc, 16.5 cc and 18.9 cc, respectively, and mean doses were 43.9 Gy, 38.6 Gy and 19.5 Gy. For breast volumes of <800 cc, 800-999 cc, 1000-1199 cc and >1200 cc, mean A1 V95 was 38%, 51%, 61.2% and 57.2% whereas median A2 V95 was 8.3%, 13.4%, 19.4% and 28% respectively. Regarding shape, where the breast relative position to the TE was categorized in intervals between 31% and 40%, 41% and 50%, 51% and 60%, and 61% and 70%, mean A1 V95 was 38.7%, 43.1%, 51.1% and 77.3% whereas mean A2 V95 was 6.1%, 11.2%, 17.1% and 37% respectively.
  
  
  CONCLUSIONS
  We observed inadequate dose coverage to all axillary levels, even after applying a sub-analysis accounting for different breast volumes and shapes. Although higher doses were associated with the more voluminous and pendulous breasts, axillary coverage with 3D-WBRT seems to be inefficient, regardless of the breast morphology.
authors.affiliation: Serviço de Radioterapia Externa, Instituto Português de Oncologia do Porto Francisco Gentil, E.P.E., Portugal. Electronic address: artur.med.aguiar@gmail.com.
authors.forename: Artur
authors.initials: A
authors.lastname: Aguiar
authors.affiliation: Serviço de Radioterapia Externa, Instituto Português de Oncologia do Porto Francisco Gentil, E.P.E., Portugal.
authors.forename: Helena
authors.initials: H
authors.lastname: Gomes Pereira
authors.affiliation: Serviço de Radioterapia Externa, Instituto Português de Oncologia do Porto Francisco Gentil, E.P.E., Portugal.
authors.forename: Isabel
authors.initials: I
authors.lastname: Azevedo
authors.affiliation: Serviço de Física Médica, Instituto Português de Oncologia do Porto Francisco Gentil, E.P.E., Portugal.
authors.forename: Luciano
authors.initials: L
authors.lastname: Gomes
mesh_terms: D000328:Adult; D000368:Aged; D001365:Axilla / Q000528:radiation effects; D001940:Breast / Q000473:pathology; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008875:Middle Aged; D009929:Organ Size; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
keywords: Axillary dose; Breast cancer; Breast shape; Breast volume