CT-planned internal mammary node radiotherapy in the DBCG-IMN study: benefit versus potentially harmful effects

Acta Oncol. 2014 Aug;53(8):1027-34. doi: 10.3109/0284186X.2014.925579. Epub 2014 Jun 24.


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).

Material and 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.

Conclusion: 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.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Breast Neoplasms / diagnostic imaging
  • Breast Neoplasms / mortality
  • Breast Neoplasms / radiotherapy*
  • Breast Neoplasms / surgery
  • Cohort Studies
  • Female
  • Heart / radiation effects
  • Humans
  • Lung / radiation effects
  • Lymph Nodes / radiation effects*
  • Lymphatic Irradiation / methods*
  • Middle Aged
  • Myocardial Ischemia / mortality
  • Neoplasm, Residual
  • Numbers Needed To Treat
  • Organs at Risk / diagnostic imaging
  • Organs at Risk / radiation effects
  • Radiography
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods*
  • Radiotherapy, Image-Guided / methods*
  • Radiotherapy, Image-Guided / mortality