Incidence of hypothyroidism after treatment for breast cancer: A Korean population-based study

Normal tissue complication probability models of hypothyroidism after radiotherapy for breast cancer

Purpose

We aimed to develop Lyman-Kutcher-Burman (LKB) and multivariable normal tissue complication probability (NTCP) models to predict the risk of radiation-induced hypothyroidism (RIHT) in breast cancer patients.

Materials and methods

A total of 1,063 breast cancer patients who underwent whole breast irradiation between 2009 and 2016 were analyzed. Individual dose-volume histograms were used to generate LKB and multivariable logistic regression models. LKB model was fit using the thyroid radiation dose-volume parameters. A multivariable model was constructed to identify potential dosimetric and clinical parameters associated with RIHT. Internal validation was conducted using bootstrapping techniques, and model performance was evaluated using the area under the curve (AUC) and Hosmer-Lemeshow (HL) goodness-of-fit test.

Results

RIHT developed in 4 % of patients with a median follow-up of 77.7 months. LKB and multivariable NTCP models exhibited significant agreement between the predicted and observed results (HL P values > 0.05). The multivariable NTCP model outperformed the LKB model in predicting RIHT (AUC 0.62 vs. 0.54). In the multivariable model, systemic therapy, age, and percentage of thyroid volume receiving ≥ 10 Gy (V10) were significant prognostic factors for RIHT. The cumulative incidence of RIHT was significantly higher in patients who exceeded the cut-off values for all three risk predictors (systemic therapy, age ≥ 40 years, and thyroid V10 ≥ 26 %, P < 0.005).

Conclusions

Systemic therapy, age, and V10 of the thyroid were identified as strong risk factors for the development of RIHT. Our NTCP models provide valuable insights to clinicians for predicting and preventing hypothyroidism by identifying high-risk patients.

Hypothyroidism Evaluation after Radiotherapy of Breast and Supraclavicular in Patients with Breast Cancer

Background

This study aims to evaluate the risk of hypothyroidism (HT) after radiotherapy (RT) of breast and supraclavicular in patients with breast cancer (BC).

Materials and Methods

In a historical cohort study, the records of all patients with BC who had been referred to the Mahdieh radiotherapy Center of Hamadan from 2017 to 2019 were reviewed. Demographic characteristics, clinical information, previous and current used treatment methods (surgery, radiotherapy, chemotherapy), number of RT sessions and doses, and HT (TSH >5 mIU/L) were extracted from the patient's documents. Data were analyzed using SPSS software version 16.

Results

Out of 304 patients referred to the Center, 266 patients were investigated. The mean TSH was 6.3 ± 7.9 ml/L (1.5 to 65.4). Approximately half of the patients were in Stage 2 of the disease. 37 (16.4%) patients were diagnosed with HT, of which 8.8% were clinical, and 7.5% were subclinical. The mean total dose of HT patients (5621.62 ± 491.67) was significantly higher than other patients (5304.76 ± 937.98). 21 patients (56.8%) in Stage 3 and 4 and 16 (43.2%) patients in Stages 1 and 2 had HT (P = 0.006). Spearman correlation coefficient showed that there was a significant relationship between total dose and TSH hormone (r = 0.624), the number of RT sessions with TSH hormone (r = 0.237), and total dose with T4 hormone (r = -0.232).

Conclusion

The findings of this study showed that the risk of HT increases significantly in patients with BC who undergo RT of breast and supraclavicular. Patients with higher stage, more radiation, and more RT sessions are at higher risk of HT.