Dosimetric Comparison Between 3D Conformal Radiation Therapy Plus Electron Boost and Simultaneous Integrated Boost Volumetric Modulated Arc Therapy for Left-Sided Breast Cancer Patients With a Potential Risk of Radiation-Induced Cardiac Toxicity.

PURPOSE/OBJECTIVE(S) Reducing radiation doses to the heart and/or cardiac segments are crucial to decrease the risk of radiation-induced coronary artery diseases (RICAD) for patients with left-sided breast cancer. However, dosimetric advantages for these structures between three-dimensional conformal radiation therapy plus electron boost (3D-CRT+EB) and simultaneous integrated boost volumetric modulated arc therapy (SIB-VMAT) remain unclear, especially in the patients with a potential risk of RICAD. The aim of this study was to compare some dosimetric parameters between the 3D-CRT + EB and SIB-VMAT in left-sided breast cancer patients with a potential risk of RICAD. MATERIALS/METHODS A total of 57 patients with left-sided breast cancer treated with SIB-VMAT between 2018 and 2020 were enrolled. All patients were identified as the potential risk of RICAD by radiation oncologists using maximum heart distance (MHD), and met the MHD ≧ 1 cm. All patients were prescribed a dose of 42.56 Gy/ 16 fractions to planning target volume and a total dose of 53.2 Gy (N = 21) or 51.2 Gy (N = 36) for a concomitant-boosted target. The 3D-CRT + EB plans were retrospectively created for a comparison purpose, using field-in-field technique followed by electron beam irradiations. Some dosimetric parameters for clinical target volume (CTV), heart, left anterior descending coronary artery (LAD), middle LAD (mLAD), lungs, and contralateral breast were compared using the Wilcoxon signed rank test. RESULTS The Dmean, Dmax and D98% for CTV were significantly improved in the SIB-VMAT plans. For cardiac-related structures, the median doses of SIB-VMAT versus 3D-CRT + EB were as follows: Dmean for heart, 2.9 Gy vs. 1.9 Gy (P < 0.001); Dmean, V20 and V30 for LAD, 12.6 Gy vs. 15.4 Gy (P < 0.001), 23.0% vs. 33.3% (P = 0.0049) and 2.0% vs. 24.7% (P < 0.001); Dmean, V20 and V30 for mLAD, 16.0 Gy vs. 21.1 Gy (P = 0.0014), 29.9% vs. 51.4% (P = 0.0040) and 0.5% vs. 31.1% (P < 0.001), respectively. The Dmean, V5 and V20 for the lungs and the Dmean for contralateral breast were significantly reduced in the 3D-CRT + EB plans (P < 0.001, for all). The doses to the LAD and mLAD tended to be higher in lateral cohort (upper outer and lower outer quadrants of breast) than in medial cohort (upper inner and lower inner quadrants of breast), while these doses were significantly reduced by the SIB-VMAT. CONCLUSION Although 3D-CRT + EB technique can reduce the mean dose to the heart, the doses to LAD and mLAD can be significantly decreased by SIB-VMAT, which could be a benchmark for selecting the most appropriate irradiation technique in the patients with a potential risk of RICAD.