为了研究乳腺癌患者接受体积调强弧治疗（VMAT）进行局部淋巴结区域放疗（RNI）期间，甲状腺功能紊乱与甲状腺辐射剂量的关联性，我们回顾了2018年至2021年期间接受根治性手术后辅助放疗，包括VMAT治疗的67名乳腺癌患者的医疗数据。所有患者的甲状腺功能测试结果，包括促甲状腺激素（TSH），T3和游离T4均正常。我们将亚临床甲状腺功能减退定义为VMAT完成后TSH升高，并可能伴有游离T4和T3水平降低。我们计算了剂量容积直方图参数（DVHPs），包括平均剂量和接受至少10、20、30和40Gy的相对甲状腺体积。 中位随访时间为23.2个月。3年局部区域无复发生存率、进展生存率和总生存率分别为96.3%、94.7%和96.2%。平均甲状腺剂量为21.4Gy（范围为11.5-29.4Gy）。14名患者（20.9%）出现亚临床甲状腺功能减退，发生事件的中位时间为4.1个月。在DVHPs中，接受≥20Gy（V20Gy）的相对体积与亚临床甲状腺功能减退有关。接受V20Gy ≤ 46.3%和> 46.3%的患者，2年亚临床甲状腺功能减退率分别为24.8%和59.1%。 一部分乳腺癌患者在接受VMAT进行RNI后发展出亚临床甲状腺功能减退。我们的研究结果强调了在VMAT计划中将甲状腺视为风险器官的重要性，并建议V20Gy可能是一个有用的剂量容积约束。 版权所有 © 2023，国际抗癌研究学院（Dr. George J. Delinasios）

To investigate the association between the thyroid dysfunction and thyroid radiation dose in regional nodal irradiation (RNI) using volumetric modulated arc therapy (VMAT) for breast cancer.We reviewed medical data of 67 patients with breast cancer who underwent curative surgery followed by adjuvant radiotherapy, including RNI using VMAT, between 2018 and 2021. All patients had normal thyroid functional test results, including thyroid stimulating hormone (TSH), T3, and free-T4. We defined subclinical hypothyroidism as increased TSH with or without decreased levels of free-T4 and T3 after the completion of VMAT. We calculated dose-volume histogram parameters (DVHPs), including the mean dose and relative thyroid volume receiving at least 10, 20, 30, and 40 Gy.The median follow-up time was 23.2 months. The 3-year locoregional failure-free survival, progression-free survival, and overall survival rates were 96.3%, 94.7%, and 96.2%, respectively. The mean thyroid dose was 21.4 Gy (range=11.5-29.4 Gy). Subclinical hypothyroidism was noted in 14 patients (20.9%) and the median time to the event was 4.1 months. Among the DVHPs, the relative volume receiving ≥20 Gy (V20Gy) was associated with subclinical hypothyroidism. The 2-year rates of subclinical hypothyroidism were 24.8% and 59.1% in patients with V20Gy ≤46.3% and >46.3%, respectively.A significant proportion of patients with breast cancer developed subclinical hypothyroidism after undergoing VMAT for RNI. Our findings highlight the importance of considering the thyroid as an organ at risk for VMAT planning, and suggest that V20Gy could be a useful dose-volume constraint.Copyright © 2023, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.