Thyroid Dosimetry in Breast Cancer Patients Receiving Post-Mastectomy Radiotherapy: A Retrospective Analysis

Abstract

Background: Breast cancer is the most frequently diagnosed cancer in women and continues to be a significant contributor to cancer-related deaths worldwide. The management of advanced stages generally involves a combination of treatment modalities such as surgery, chemotherapy, and adjuvant radiotherapy. During post-mastectomy chest wall and supraclavicular irradiation, a portion of the thyroid gland may inadvertently receive radiation exposure, potentially leading to hypothyroidism. This study aimed to evaluate thyroid gland dosimetry in patients undergoing post-mastectomy radiotherapy using 3D-CRT. Materials and Methods: Thirty patients with histologically confirmed breast carcinoma who had undergone MRM were included. All patients received PMRT to the chest wall and supraclavicular region using the 3D conformal radiotherapy technique, with a total prescribed dose of 50 Gy delivered in 25 fractions. The thyroid gland was delineated for each patient and dosimetric parameters—thyroid volume, mean, minimum, and maximum doses, and percentage volume receiving 30 Gy were calculated and analyzed. Results: The patients ranged in age from 37 to 71 years. The mean thyroid gland volume was 15.63 cc. The mean dose to the entire thyroid gland was 19.05 Gy, with mean minimum and maximum doses of 0.676 Gy and 52.67 Gy, respectively. The mean thyroid V30 was 32.98%, while the ipsilateral thyroid V30 averaged 66.36%. Conclusion: Post-mastectomy radiotherapy involving the supraclavicular region exposes the thyroid gland to significant radiation doses, increasing the risk of hypothyroidism. The thyroid gland should be recognized as an organ at risk during radiotherapy planning, and periodic assessment of thyroid function is essential for the early detection and timely management of radiation-induced hypothyroidism.