Prevalence of poor cardiac anatomy in carcinoma of the breast treated with whole-breast radiotherapy: reconciling modern cardiac dosimetry with cardiac mortality data
Department of Radiation Oncology
Medical Subject Headings
Adult; Aged; Aged, 80 and over; Body Mass Index; Breast; Breast Neoplasms; Carcinoma; Coronary Artery Disease; Female; Heart; Humans; Middle Aged; Multivariate Analysis; Organ Size; Radiation Injuries; Radiotherapy Dosage
Neoplasms | Oncology
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.
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Citation: Am J Clin Oncol. 2012 Dec;35(6):587-92. doi: 10.1097/COC.0b013e31822d9cf6. Link to article on publisher's site