Predictive Factors for Thyroid Complications After Radiation Therapy

Data From a Cohort of Cancer Patients Closely Followed Since They Were Irradiated

Vitoria Duarte; Joana Maciel; Daniela Cavaco; Sara Donato; Inês Damásio; Sara Pinheiro; Ana Figueiredo; Ana Ferreira; Joana S. Pereira


Clin Endocrinol. 2022;96(5):728-733. 

In This Article

Patients and Methods

We performed a retrospective study that included 282 cancer patients followed at our endocrine cancer late-effects outpatient clinic. These subjects were patients of any age who received external beam radiotherapy (RT) to the neck, craniospinal irradiation (CSI), or total body irradiation (TBI) preceding hematopoietic stem cell transplantation. Patients had their primary cancer diagnosis between 1972 and 2015. The study was conducted at the Instituto Português de Oncologia Francisco Gentil, in Lisbon. The time period for data extraction was October–December 2020. This study was approved by the Ethics Committee of our centre.

Patients were clustered into four diagnostic groups, formed according to the type of malignancy: leukaemia, HD, central nervous system (CNS), and head or neck tumours (HNT). Eight non-Hodgkin lymphoma (NHL) patients were grouped with either Leukaemia or HD patients in line with treatment modality (TBI vs. neck irradiation). RT data were collected from patients' medical records including time of treatment, dose, and field of irradiation.

Subjects were excluded based on the following criteria: diagnosis of thyroid nodules, thyroid cancer, hyperthyroidism or hypothyroidism before RT; prior prescription of levothyroxine, thiamazole, or propylthiouracil at any time; prior radioactive iodine therapy; prior thyroid surgery; and diagnosis of central hypothyroidism after RT.

Thyroid function was evaluated routinely after the completion of RT by measuring thyroid-stimulating hormone (TSH) and free thyroxine (T4). Thyroid autoimmunity was investigated by the measurement of serum antithyroid peroxidase antibodies and antithyroglobulin antibodies. Primary hypothyroidism was defined as serum TSH above the normal range (0.30–4.5 mIU/L) on two consecutive measurements and low T4. Thyroid parenchyma was evaluated by an experienced ultrasound radiologist. A fine-needle aspiration biopsy was performed when considered appropriate according to standard clinical practice.

Categorical variables are presented as absolute numbers and percentages. Gaussian distribution of continuous variables was determined with Shapiro–Wilk test; normally distributed variables are shown as mean ± standard deviation and non-normally variables are presented as median (interquartile range [IQR]; minimum–maximum). Categorical variables were compared using the χ 2 test. All continuous variables described as mean ± standard deviation were compared using the Student t-test.

Independent factors associated with the development of thyroid abnormalities (dysfunction and nodules/cancer) were identified with binary logistic regression.

A p < .05 was considered statistically significant. Data collection and registration were made in Microsoft Excel (Microsoft). Statistical analysis was performed with IBM SPSS Statistics version 25 (IBM Corp).