Taylor C, et al. - Researchers investigated the impact of breast cancer radiotherapy on specific cardiac segments. In relation to receipt of higher radiation doses, more frequent injury was strongly detected for individual left ventricular (LV) and coronary artery segments. This indicated the sensitivity of all segments to radiation. Minimizing doses to all segments is recommended.

Methods

• Researchers gathered data on the radiotherapy regimen and on the location of the cardiac injury for 456 women who received breast cancer radiotherapy between 1958 and 2001 and then later had a major coronary event.
• They estimated doses to five LV segments for 414 women, all with documented left ventricular (LV) injury.
• They also estimated doses to six coronary artery segments for 133 women, all with documented coronary artery disease with ≥ 70% stenosis.
• They compared numbers of women with left-sided and right-sided breast cancer for each segment.

Results

• Left-sided breast cancer was present in 243 and right-sided breast cancer in 171 (ratio of left v right, 1.42; 95% CI, 1.17 to 1.73) of women with LV injury, indicating the higher typical LV radiation doses in left-sided cancer (average dose left-sided, 8.3 Gy; average dose right-sided, 0.6 Gy; left minus right dose difference, 7.7 Gy).
• The reported ratios of women with left- vs right-sided radiotherapy for individual LV segments were as follows: inferior, 0.94 (95% CI, 0.70 to 1.25); lateral, 1.42 (95% CI, 1.04 to 1.95); septal, 2.09 (95% CI, 1.37 to 3.19); anterior, 1.85 (95% CI, 1.39 to 2.46); and apex, 4.64 (95% CI, 2.42 to 8.90); corresponding left-minus-right dose differences for these segments were 2.7, 4.9, 7.2, 10.4, and 21.6 Gy, respectively (P_trend < .001).
• The ratios of women with left- vs right-radiotherapy for individual coronary artery segments reported for women with coronary artery disease were as follows: right coronary artery proximal, 0.48 (95% CI, 0.26 to 0.91); right coronary artery mid or distal, 1.69 (95% CI, 0.85 to 3.36); circumflex proximal, 1.46 (95% CI, 0.72 to 2.96); circumflex distal, 1.11 (95% CI, 0.45 to 2.73); left anterior descending proximal, 1.89 (95% CI, 1.07 to 3.34); and left anterior descending mid or distal, 2.33 (95% CI, 1.19 to 4.59); corresponding left-minus-right dose differences for these segements were -5.0, -2.5, 1.6, 3.5, 9.5, and 38.8 Gy (P_trend = .002).