Left-sided breast cancer patients undergoing radiation therapy have a higher risk of cardiac mortality. Advanced techniques like t-IMRT, t-VMAT, and deep inspiratory breath-hold (DIBH) can help reduce side effects by sparing organs at risk. Recent studies suggest considering dose parameters of the left ventricle (LV), left anterior descending artery (LAD), and mean heart dose for better results. A retrospective study was conducted to evaluate the dose parameters of the heart and its substructures. The DIBH treatment plans of 12 patients with left-sided breast cancer (LSBC) were analyzed. The contours of the heart, LV, and LAD were regenerated. Then the 3D dose distribution was recalculated and compared the results with the QUANTEC criteria and recently proposed stricter criteria. Heart mean dose was <26 Gy for all plans. 8/12 plans met V25 criteria, all met V30. 2 plans had mean heart dose of 2.5 Gy but failed for LAD and LV. Only 1 plan met criteria for LV. The study found that shifting LAD towards the posterior direction reduced its dose parameters compared to shifting it towards the anterior direction. However, none of the adjustments made met the required criteria. The investigation underlines the importance of strict criteria for critical heart substructures during treatment planning.

Keywords