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Dosimetric Study of Intensity-Modulated Radiotherapy to the Axilla after Breast-Conserving Surgery for Breast Cancer |
NI Wenjie, WANG Qin, WANG Xiunan, et al |
Beijing Shijitan Hospital, Capital Medical University, Beijing 100038, China |
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Abstract Objective: To evaluate the dosimetric characteristics of axillary nodes with intensity modulated radiotherapy after breast conserving surgery. Methods: From November 2020 to November 2021, 16 consecutive left breast cancer patients were enrolled after breast conserving surgery. According to the ESTRO guidelines, the axillary level I and level II + interpectoral nodes were delineated. Four regimens are prepared: intensity-modulated radiotherapy based on tangential field for whole breast target (IMRT) or whole breast + axillary nodes target (IMRTn), volume modulated arc therapy for whole breast target (VMAT) or whole breast + axillary nodes target (VMATn). The prescription dose is 50 Gy per 25 fractions, and the relevant dosimetric parameters of each regimen are recorded. Results: The mean doses delivered to axillary nodes by IMRT and VMAT were (33.2±7.3) Gy and (32.6±7.4) Gy for level I (P = 0.477), (32.4±7.5) Gy and (30.2±7.8) Gy for level II + interpectoral nodes (P<0.001), respectively. The conformal index of IMRTn and IMRT were (0.698±0.05) and (0.753±0.03), (P = 0.001), (0.835±0.03) for VMATn and (0.857±0.04) for VMAT, (P = 0.018). The mean doses to ipsilateral lung by IMRT, IMRTn, VMATn were (10.3±1.2) Gy, (11.2±1.0) Gy and (10.5±0.8) Gy, respectively (P = 0.040). The V5 (volume receiving 5 Gy) to ipsilateral lung by IMRT, IMRTn, VMATn were (33.4±3.5)%, (38.5±3.7)% and (40.5±3.1)%, respectively (P<0.001). The mean doses to contralateral breast were (1.5±0.4) Gy, (1.7±0.7) Gy and (2.3±0.8) Gy, respectively (P = 0.006). Conclusion: The dose of axillary nodes was insufficient during whole breast radiotherapy. Whole breast + axillary area irradiation could deliver adequate prescription dose, and increase little dose to the normal tissues, but they were all lower than required dose constraints.
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