Evaluation of Thyroid Gland Irradiation in Women with Breast Cancer during Radiotherapy with different Radiation Energies at Supraclavicular Region

Introduction: During treatment of breast cancer, Radiotherapy to the Supraclavicular fossa region results in absorption of radiation by the thyroid gland and consequently leads to hypothyroidism in 40% of patients. The aim of this study was to compare thyroid gland radiation absorption during radiotherapy with different anterior-posterior beam radiation of 6-15 and 15-15 MV photon beam energies. Materials and Methods: 29 patients with breast cancer were recruited to this study. Adjuvant radiotherapy with a total dose of 50 Gy was performed for each participant. Thyroid gland dosimetric measurements were evaluated including, mean dose, minimum and maximum dose, and V20, V30, V40, and V50 (percentage of thyroid volume receiving ≥20 Gy, ≥30 Gy, ≥40 Gy, and ≥50 Gy, respectively). The irradiation delivered doses were measured using Prowess Panther treatment planning system (Version 5.5). All data were evaluated using SPSS software. Results: 29 subjects with mean age of 53.4±9.4 were studied. According to the obtained results, at 15- 15 MV energies, a significantly lower dose was absorbed by the thyroid gland, was observed in contrast to their counterparts who were treated with 6-15 MV photon beam energies. Conclusion: Using 15-15 MV photon beam energies field can significantly reduce the absorbed dose to the thyroid gland and consequently can reduce the risk of developing hypothyroidism in breast cancer patients treated with radiotherapy.