Prevalence of poor cardiac anatomy in carcinoma of the breast treated with whole-breast radiotherapy: reconciling modern cardiac dosimetry with cardiac mortality data

Am J Clin Oncol. 2012 Dec;35(6):587-92. doi: 10.1097/COC.0b013e31822d9cf6.

Abstract

Purpose: : 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 and materials: : 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.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Body Mass Index
  • Breast / anatomy & histology*
  • Breast Neoplasms / radiotherapy*
  • Carcinoma / radiotherapy*
  • Coronary Artery Disease / etiology
  • Coronary Artery Disease / mortality*
  • Female
  • Heart / anatomy & histology*
  • Heart / radiation effects
  • Humans
  • Middle Aged
  • Multivariate Analysis
  • Organ Size
  • Radiation Injuries / etiology
  • Radiotherapy Dosage