For radiotherapy in patients with left-sided breast cancer, the deep inspiration breath-hold(DIBH) technique has been introduced to reduce cardiac toxicity and lower the risk of mortality due to cardiovascular complications. This technique was studied in 25 patients who had two sets of image data for DIBH and free-breathing (FB) treatments. The dose data from the FB and DIBH plans were then analyzed and compared. Additionally,the mean dose and dose-volume parameters for the heart, left ventricle (LV), and left anterior descending (LAD) artery were calculated and analyzed. Stricter criteria have been applied to these values, and the current treatment plans have been reviewed. Our results show that radiation doses to cardiac substructures, such as the LV and LAD artery, do not meet the stricter criteria in nearly all cases. Since radiation dose to these substructures is crucial in preventing late cardiac complications, relying solely on the DIBH technique is not enough for protecting the heart. It is essential to consider these substructures during the treatment planning phase for patients with left-sided breast cancer. Additionally, there should be an exploration of newer techniques that can help achieve the stricter criteria for protecting heart substructures.

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