Thyroid volume changes following adjuvant radiation therapy for breast cancer

John Roberson; Huakang Huang; Collin Noldner; Wei Hou; Kartik Mani; Edward Valentine; Samuel Ryu; Alexander Stessin

doi:10.1016/j.ctro.2022.100566

Thyroid volume changes following adjuvant radiation therapy for breast cancer

Clin Transl Radiat Oncol. 2022 Dec 16:39:100566. doi: 10.1016/j.ctro.2022.100566. eCollection 2023 Mar.

Authors

John Roberson¹, Huakang Huang², Collin Noldner¹, Wei Hou³, Kartik Mani^{1

4}, Edward Valentine¹, Samuel Ryu^{1

5}, Alexander Stessin^{1

5}

Affiliations

¹ Department of Radiation Oncology, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA.
² Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA.
³ Department of Family, Population, and Preventive Medicine, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA.
⁴ Department of Biomedical Informatics, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA.
⁵ Department of Pharmacology, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA.

Abstract

Background and purpose: Incidental thyroid gland irradiation frequently occurs in breast cancer patients who receive regional nodal irradiation (RNI) to the supraclavicular (SCV) region. Recent studies suggest hypothyroidism (HT) is a complication of radiation therapy (RT) that includes SCV fields. We retrospectively analyzed patients who received RNI to evaluate thyroid gland evolution following RT as well as its association with the development of HT.

Materials and methods: 61 breast cancer patients received SCV-directed RT between 2007 and 2019 and met inclusion criteria. Thyroid glands were retrospectively contoured on CT simulation and follow-up images. Individual dose-volume histograms were analyzed to determine thyroid volume within and outside specific isodose lines. Relative thyroid volume changes based on different radiation doses were estimated by fusing post-RT scans with CT simulation. Logistic regression was performed to assess thyroid volume changes as a factor in the development of HT.

Results: Median pre-treatment thyroid volume was 11.8 cc (range: 6.3-74.1 cc) with a median of 42.2 % within the 20 Gy and 23.2 % within the 40 Gy isodose lines. A significant decrease in thyroid volume was noted by 1-year post-treatment (p < 0.0001) and thereafter. By 4 years post-treatment, average thyroid volume was decreased by 29.7 % (range: 2.3-64.4 %). Thyroid volume receiving 40 Gy or higher demonstrated a greater decrease compared to those receiving lower irradiation dosage. HT occurred in 17 patients (27.9 %). Patients who developed HT displayed a larger decrease in the thyroid volume receiving between 20 and 40 Gy at 12 months (p = 0.033).

Conclusion: Our study demonstrates for the first time that a reduction in thyroid volume may be seen as early as 6 months after SCV-directed RT for breast cancer, which correlates with development of clinical and subclinical HT. Furthermore, a dose-dependent correlation exists between thyroid subvolume reduction and SCV-directed RT in breast cancer patients. As feasible, efforts should be made to reduce the dose to the thyroid in patients who undergo RNI for breast cancer.

Keywords: Breast Neoplasms; Cancer survivors; HT, hypothyroidism; Hypothyroidism; RNI, regional nodal irradiation; RT, radiation therapy; Radiotherapy dosage; Radiotherapy, conformal; Radiotherapy, intensity-modulated; Retrospective studies; SCV, supraclavicular; Thyroid evolution.