Dosimetry of the left anterior descending coronary artery in left breast cancer patients treated with postoperative external radiotherapy.

Aim: To evaluate the dose distribution to the left anterior descending (LAD) coronary artery in patients treated with postoperative three-dimensional conformal radiotherapy (3DCRT).

Background: Postoperative radiotherapy may increase the risk of heart disease, particularly in patients with left-sided breast cancer. Clinical data on doses to the LAD are limited.

Materials and methods: Retrospective study of 14 patients who underwent postoperative 3DCRT for left breast cancer in 2014. All data were retrieved from medical records. Means, medians, ranges, and percentages were calculated.

Results: The mean dose to the LAD in patients with V25 < 1% was 0.12 cGy. D mean , D max and V25 to the heart were, respectively, 3.7 Gy (range, 0.9-4.18), 40.3 Gy (9.28-62.9), and 1.59 cGy. The mean D mean and D max values in the sample were 9.71 Gy and 33.2 Gy, respectively. The maximum dose to the LAD (D2%) ranged from 3.66 to 53.01 Gy. Due to the spacing of the CT slices (5 mm), it was not possible to completely contour the entire artery. The mean dose to the heart (3.3 Gy) was considered acceptable.

Conclusions: The maximum dose to the LAD was as high as 53 Gy, suggesting an increased risk of cardiac morbidity. This study underscores the value of contouring the LAD and the value of the breath hold technique to reduce maximum cardiac doses. Smaller CT cuts (2.5 mm) can improve contouring. Larger studies with long-term follow up are needed to determine the radiation tolerance dose for the LAD.