title: CT-planned internal mammary node radiotherapy in the DBCG-IMN study: benefit versus potentially harmful effects.
abstract: BACKGROUND
  The DBCG-IMN is a nationwide population-based cohort study on the effect of internal mammary node radiotherapy (IMN-RT) in patients with node positive early breast cancer. Due to the risk of RT-induced heart disease, only patients with right-sided breast cancer received IMN-RT, whereas patients with left-sided breast cancer did not. At seven-year median follow-up, a 3% gain in overall survival with IMN-RT has been reported. This study estimates IMN doses and doses to organs at risk (OAR) in patients from the DBCG-IMN. Numbers needed to harm (NNH) if patients with left-sided breast cancer had received IMN-RT are compared to the number needed to treat (NNT).
  
  
  METHODS
  Ten percent of CT-guided treatment plans from the DBCG-IMN patients were selected randomly. IMNs and OAR were contoured in 68 planning CT scans. Dose distributions were re-calculated. IMNs and OAR dose estimates were compared in right-sided versus left-sided breast cancer patients. In six left-sided patients, IMN-RT was simulated, and OAR doses were compared to those in the original plan. The NNH resulting from the change in mean heart dose (MHD) was calculated using a published model for risk of RT-related ischemic heart death.
  
  
  RESULTS
  In original plans, the absolute difference between right- and left-sided V90% to the IMNs was 38.0% [95% confidence interval (5.5%; 70.5%), p < 0.05]. Heart doses were higher in left-sided plans. With IMN-RT simulation without regard to OAR constraints, MHD increased 4.8 Gy (0.9 Gy; 8.7 Gy), p < 0.05. Resulting NNHs from ischemic heart death were consistently larger than the NNT with IMN-RT.
  
  
  CONCLUSIONS
  Refraining from IMN-RT on the left side may have spared some ischemic heart deaths. Assuming left-sided patients benefit as much from IMN-RT as right-sided patients, the benefits from IMN-RT outweigh the costs in terms of ischemic heart death.
authors: Department of Experimental Clinical Oncology, Aarhus University Hospital , Denmark.
authors: Lise B J
authors: LB
authors: Thorsen
authors: Mette S
authors: MS
authors: Thomsen
authors: Martin
authors: M
authors: Berg
authors: Ingelise
authors: I
authors: Jensen
authors: Mirjana
authors: M
authors: Josipovic
authors: Marie
authors: M
authors: Overgaard
authors: Jens
authors: J
authors: Overgaard
authors: Peter
authors: P
authors: Skogholt
authors: Birgitte V
authors: BV
authors: Offersen
mesh_terms: D000465:Algorithms; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000401:mortality / Q000532:radiotherapy* / Q000601:surgery; D015331:Cohort Studies; D005260:Female; D006321:Heart / Q000528:radiation effects; D006801:Humans; D008168:Lung / Q000528:radiation effects; D008198:Lymph Nodes / Q000528:radiation effects*; D015182:Lymphatic Irradiation / Q000379:methods*; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000401:mortality; D018365:Neoplasm, Residual; D061366:Numbers Needed To Treat; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods* / Q000401:mortality