title: Prevalence of poor cardiac anatomy in carcinoma of the breast treated with whole-breast radiotherapy: reconciling modern cardiac dosimetry with cardiac mortality data.
abstract: OBJECTIVE
  : The purpose of the study was to identify patient characteristics that predict for increased cardiac exposure through dosimetric analysis of the anatomy of a cohort of women treated with left-sided tangential breast radiation. Statistical analyses estimations for the appropriate sample sizes required for detection of significant differences in cardiac mortality at 15 years were conducted, assuming a threshold V25 for radiation-induced coronary artery disease (CAD) beyond which women are at risk for radiation-induced coronary artery disease.
  
  
  METHODS
  : Detailed heart dosimetry was recorded. Clinical factors (age, history of CAD, diabetes, receipt of cardiotoxic agents, weight/body mass index) and anatomic factors (heart volume, breast volume, cardiac contact distance) were recorded for each patient.
  
  
  RESULTS
  : The average heart V25 was 3.57%. The median percentage of the heart included in the tangential beam was 4.02%. There were no clinical or anatomic factors that predict suboptimal heart anatomy (ie, V25 of ≥6%) on multivariate analysis. The sample size calculations using thresholds for induction of CAD of V25 ≥1%, 6%, and 10% yielded sample sizes of 1314, 9504, and 61,342, respectively; considering node-positive breast cancer mortality and 15% loss to follow-up, these change to 2237, 16,166, and 104,334, respectively.
  
  
  CONCLUSIONS
  : Current studies with modern radiotherapy techniques would be underpowered to detect a difference in cardiac mortality where only some women are at risk. The heart, chest wall, and breast have a complex relationship to tangential breast radiation, and their interplay prevented this anatomic metric's success.
authors.affiliation: Department of Therapeutic Radiology Yale University, New Haven, CT 06510, USA. Suzanne.evans@yale.edu
authors.forename: Suzanne B
authors.initials: SB
authors.lastname: Evans
authors.forename: Shirin
authors.initials: S
authors.lastname: Sioshansi
authors.forename: Meena S
authors.initials: MS
authors.lastname: Moran
authors.forename: Jessica
authors.initials: J
authors.lastname: Hiatt
authors.forename: Lori Lyn
authors.initials: LL
authors.lastname: Price
authors.forename: David E
authors.initials: DE
authors.lastname: Wazer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D001940:Breast / Q000033:anatomy & histology*; D001943:Breast Neoplasms / Q000532:radiotherapy*; D002277:Carcinoma / Q000532:radiotherapy*; D003324:Coronary Artery Disease / Q000209:etiology / Q000401:mortality*; D005260:Female; D006321:Heart / Q000033:anatomy & histology* / Q000528:radiation effects; D006801:Humans; D008875:Middle Aged; D015999:Multivariate Analysis; D009929:Organ Size; D011832:Radiation Injuries / Q000209:etiology; D011879:Radiotherapy Dosage