title: Postoperative proton radiotherapy for localized and locoregional breast cancer: potential for clinically relevant improvements?
abstract: OBJECTIVE
  To study the potential reduction of dose to organs at risk (OARs) with intensity-modulated proton radiotherapy (IMPT) compared with intensity-modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy (3D-CRT) photon radiotherapy for left-sided breast cancer patients.
  
  
  METHODS
  Comparative treatment-planning was performed using planning computed tomography scans of 20 left-sided breast cancer patients. For each patient, three increasingly complex locoregional volumes (planning target volumes [PTVs]) were defined: whole breast (WB) or chest wall (CW) = (PTV1), WB/CW plus medial-supraclavicular (MSC), lateral-supraclavicular (LSC), and level III axillary (AxIII) nodes = (PTV2) and WB/CW+MSC+LSC+AxIII plus internal mammary chain = (PTV3). For each patient, 3D-CRT, IMRT, and IMPT plans were optimized for PTV coverage. Dose to OARs was compared while maintaining target coverage.
  
  
  RESULTS
  All the techniques met the required PTV coverage except the 3D-CRT plans for PTV3-scenario. All 3D-CRT plans for PTV3 exceeded left-lung V20. IMPT vs. 3D-CRT: significant dose reductions were observed for all OARs using IMPT for all PTVs. IMPT vs. IMRT: For PTV2 and PTV3, low (V5) left lung and cardiac doses were reduced by a factor >2.5, and cardiac doses (V22.5) were by a factor of >20 lower with IMPT compared with IMRT.
  
  
  CONCLUSIONS
  When complex-target irradiation is needed, 3D-CRT often compromises the target coverage and increases the dose to OARs; IMRT can provide better results but will increase the integral dose. The benefit of IMPT is based on improved target coverage and reduction of low doses to OARs, potentially reducing the risk of late-toxicity. These results indicate a potential role of proton-radiotherapy for extended locoregional irradiation in left breast cancer.
authors.affiliation: Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland. carmen.ares@psi.ch
authors.forename: Carmen
authors.initials: C
authors.lastname: Ares
authors.forename: Shaka
authors.initials: S
authors.lastname: Khan
authors.forename: Anne M
authors.initials: AM
authors.lastname: Macartain
authors.forename: Jürg
authors.initials: J
authors.lastname: Heuberger
authors.forename: Gudrun
authors.initials: G
authors.lastname: Goitein
authors.forename: Guenther
authors.initials: G
authors.lastname: Gruber
authors.forename: Gerd
authors.initials: G
authors.lastname: Lutters
authors.forename: Eugen B
authors.initials: EB
authors.lastname: Hug
authors.forename: Stephan
authors.initials: S
authors.lastname: Bodis
authors.forename: Antony J
authors.initials: AJ
authors.lastname: Lomax
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging / Q000528:radiation effects; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000528:radiation effects; D061766:Proton Therapy; D011832:Radiation Injuries / Q000517:prevention & control*; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D047368:Tumor Burden; D011522:Protons
chemical_list: D011522:Protons