Dose-Gradient Function-Guided Reduction of Radiation-Induced Heart Injury in Left-Sided Breast Cancer Treated With Helical Tomotherapy After Mastectomy.

IntroductionRadiation-induced heart injury (RIHI) remains an important concern in left-sided postmastectomy radiotherapy (PMRT), particularly when internal mammary lymph nodes (IMLNs) are included in the target volume. Helical tomotherapy (HT) provides excellent target conformity for complex targets, but cardiac sparing remains challenging. This study evaluated whether dose-gradient function (DGF)-guided optimization could further reduce cardiac exposure in left-sided breast cancer patients treated with HT after modified radical mastectomy.MethodsTwenty-six female patients with left-sided breast cancer who underwent PMRT were retrospectively included. Initial HT plan was generated and evaluated using DGF, which quantifies dose falloff outside the target volume. The patient with the minimum DGF curve area (Smin) was used as the internal benchmarking and was not re-optimized. The remaining 25 patients underwent DGF-guided re-optimization. Mean heart dose (MHD), cardiac dose-volume indices, left anterior descending coronary artery (LAD) dose, and the model-based relative risk increase (RRI) of major coronary events, were compared between the original and optimized plans.ResultsDGF-guided re-optimization significantly reduced cardiac dose parameters while maintaining target coverage and overall plan quality. MHD decreased from 6.190 ± 0.384 Gy to 5.322 ± 0.332 Gy (P < 0.001), and cardiac V5 decreased from 43.084 ± 4.807% to 29.260 ± 4.453% (P < 0.001), with significant reductions in V10, V20, and V30 (all P < 0.05). LAD V5 decreased from 86.150 ± 8.152% to 81.240 ± 9.100% (P < 0.001), and LAD mean dose decreased from 18.786 ± 2.661 Gy to 18.230 ± 2.691 Gy (P < 0.001). Greater cardiac dose reduction was observed in the IMLNs irradiation group. The estimated relative risk increase decreased from 45.803 ± 2.839% to 39.383 ± 2.459% (P < 0.001).ConclusionDGF-guided optimization may improve HT plan quality for left-sided PMRT and achieve additional reductions in cardiac dose and model-based cardiac risk estimates, particularly in cases requiring IMLNs irradiation.