Dosimetric comparison of three different radiotherapy regimens for bilateral breast cancer

Objective To compare the dosimetric characteristics of three radiotherapy techniques—VMAT, HT-5, and HT-2.5—in patients with bilateral breast cancer, and to serve as a reference for clinical plan optimization. Materials and methods For 30 patients with bilateral breast cancer, radiotherapy plans were generated using Monaco-based volumetric modulated arc therapy (VMAT) and Tomo-based helical tomotherapy with 5 cm field width (HT-5) and 2.5 cm field width (HT-2.5). The prescription dose was 50 Gy in 25 fractions. The conformity index (CI) and homogeneity index (HI) of the planning target volume (PTV) were evaluated. For organs at risk, the V 5 , V 10 , V 20 , V 30 , and mean dose ( Dmean ) of the lungs and heart, as well as the Dmean of the left anterior descending coronary artery (LAD), were analyzed. Beam-on time was recorded for each technique. Statistical analysis and data visualization were performed using R (version 4.3.2). Results All three techniques met clinical requirements for target coverage. VMAT achieved the highest CI (P < 0.05), with no significant difference in HI (P > 0.05) among the three techniques. HT-2.5 had a slightly lower Whole Lung-Dmean (10.59 ± 1.09 Gy) than VMAT (10.65 ± 0.69 Gy), but the difference was not statistically significant (P > 0.05). Whole Lung-V5% was significantly lower with HT-5 (52.61 ± 4.90%) (P < 0.05) and HT-2.5 (50.23 ± 4.43%) (P < 0.05) compared to VMAT (57.24 ± 5.37%), while VMAT had significantly lower V 10 (P < 0.05)and V 20 (P < 0.05). For the heart, HT-5 and HT-2.5 provided lower Dmean (5.71 ± 1.07 Gy and 5.40 ± 0.94 Gy) (P < 0.05,P < 0.05) and V 5 (24.25 ± 8.25% and 21.88 ± 7.37%) (P < 0.05,P < 0.05) than VMAT (6.37 ± 0.95 Gy and 49.52 ± 13.33%). However, heart V 30 was significantly lower with VMAT compared to HT-5 (P < 0.05) and HT-2.5 (P < 0.05). LAD Dmean was significantly lower with VMAT compared to HT-5 (P < 0.05) and HT-2.5(P < 0.05). Beam-on time was shortest with VMAT (4.5 ± 0.5 min), followed by HT-5 (8.1 ± 0.3 min) and HT-2.5 (14.8 ± 0.6 min). Conclusion All three techniques offer acceptable target coverage for bilateral breast cancer. VMAT provides superior target conformity, LAD sparing, and the shortest treatment time. HT-5 and HT-2.5 demonstrate advantages in cardiac protection, with lower heart Dmean and V 5 , while HT-2.5 offers the best reduction in low-dose lung exposure. Considering the combined factors of lung and heart sparing as well as overall treatment time, the Complete block type of 5 cm HT plan can also be recommended for synchronous bilateral breast cancer.