Incidence and Dose–Volume Predictors of Radiation-Induced Hypothyroidism in Patients with Locally Advanced Breast Cancer Treated with VMAT

Abstract

Radiation-induced hypothyroidism (RIHT) is an increasingly recognized late toxicity following regional nodal irradiation for breast cancer; however, thyroid dose constraints remain poorly defined, particularly in the era of modern radiotherapy. This retrospective study investigated the incidence and predictors of RIHT in 95 patients with locally advanced breast cancer treated with volumetric modulated arc therapy (VMAT) including supraclavicular irradiation. Clinical characteristics, thyroid function tests, and thyroid dose-volume parameters (V5–V50, Dmean, and Dmax) were analyzed. During a median follow-up of 30.9 months, RIHT developed in 21 patients (22.1%), and the cumulative incidence increased progressively to 24.0% at 36 months. Baseline thyroid-stimulating hormone level was the only significant predictor of RIHT, whereas no thyroid dose-volume parameter was associated with hypothyroidism. These findings suggest that patient-related susceptibility may play a greater role than dosimetric factors when contemporary thyroid-sparing VMAT planning is routinely applied, highlighting the importance of baseline thyroid assessment and long-term endocrine surveillance.

Keywords

• Breast cancer
• Radiotherapy
• Hypothyroidism

Project Number

None

Ethical Statement

The entire process of the manuscript was carried out in compliance with the research and publication ethics guidelines of the Celal Bayar University Journal of Science. Ethics committee approval was obtained from Bahcesehir University Non-interventional Studies Ethical Committee with the decision dated [2025-20/06] and numbered [E-78097791-020-5143]

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