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Dosimetric comparison of three different radiotherapy regimens for bilateral breast cancer
Fanyang Kong1, Linyan Xie2, Bingyuan Wang1
1Department of Radiation Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, 45000, China.
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 V5, V10, V20, V30, 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 V10 (P < 0.05)and V20(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 V5 (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 V30 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 V5, 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.
