title: The impact of active breathing control on internal mammary lymph node coverage and normal tissue exposure in breast cancer patients planned for left-sided postmastectomy radiation therapy.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the impact of the active breathing control (ABC) technique on IMN coverage and organs at risk in patients planned for postmastectomy radiation therapy (PMRT), with the inclusion of the internal mammary lymph nodes (IMNs). The effect of body mass index (BMI) on recorded dosimetric parameters was examined in the same patient cohort.
  
  
  METHODS
  Fifty left-sided postmastectomy patients with breast cancer who underwent free-breathing (FB) and ABC-Elekta CT simulation scans were selected at random from an institutional breast cancer database between 2008 and 2014. The ABC plans were directly compared with FB plans from the same patient.
  
  
  RESULTS
  The IMN planning target volume coverage met dosimetric criteria for coverage of receiving more than 90% of the prescribed dose (V90) >90%, although it decreased with ABC compared with FB (94.5% vs 98%, P < .001). Overall, ABC significantly reduced doses to all measured heart and left anterior descending coronary artery parameters, ipsilateral lung V20, and mean lung dose compared with FB (P < .001). There was no difference seen between the ABC and FB plans with respect to the dose to contralateral lung or contralateral breast. There was no correlation identified between BMI and any of the dosimetric parameters recorded from the ABC and FB plans.
  
  
  CONCLUSIONS
  Our results suggest that ABC reduces IMN coverage in left-sided breast cancer patients planned for PMRT; however, dosimetric criteria for IMN coverage were still met, suggesting that this is not likely to be clinically significant. ABC led to significant sparing of organs at risk compared with FB conditions and was not affected by BMI. Collectively, the results support the use of ABC for breast cancer patients undergoing left-sided PMRT requiring regional nodal irradiation that includes the IMNs. Further prospective clinical studies are required to determine the impact of these results on late normal tissue effects.
authors.affiliation: Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Aisling
authors.initials: A
authors.lastname: Barry
authors.affiliation: Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Kathy
authors.initials: K
authors.lastname: Rock
authors.affiliation: Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Claudio
authors.initials: C
authors.lastname: Sole
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Rahman
authors.affiliation: Department of Biostatistics, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada.
authors.forename: Melania
authors.initials: M
authors.lastname: Pintilie
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada.
authors.forename: Grace
authors.initials: G
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada; Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada.
authors.forename: Anthony
authors.initials: A
authors.lastname: Fyles
authors.affiliation: Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada; Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. Electronic address: anne.koch@rmp.uhn.on.ca.
authors.forename: C Anne
authors.initials: CA
authors.lastname: Koch
mesh_terms: D000328:Adult; D015992:Body Mass Index; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D062485:Breath Holding / Q000276:immunology*; D005260:Female; D006801:Humans; D008198:Lymph Nodes / Q000473:pathology; D011879:Radiotherapy Dosage; D012119:Respiration / Q000276:immunology*; D055815:Young Adult