Background: During the planning of 3D conformal radiotherapy for head and neck tumors, it is crucial to prioritize the dosage that reaches sensitive organs such as the thyroid gland. This is because there is a significant likelihood of developing thyroid dysfunction after radiotherapy, which can greatly impact the patient's quality of life. So, we aimed to evaluate thyroid gland function in H&N cancer patients after head and neck radiotherapy to correlate the relation between the RT dose and thyroid gland dysfunctions.

Methods: This prospective study was conducted in Clinical Oncology and Nuclear Medicine Department in Zagazig University Hospitals on 30 patients with head and neck carcinoma who presented to Clinical Oncology department to receive either definitive or adjuvant conformal three dimensional radiotherapy with or without concurrent chemotherapy.

Results: At 6 months of follow up, 73.3% had normal thyroid function while 26.7% had subclinical hypothyroidism and none had overt clinical hypothyroidism. However, at 12 months the rates of normal thyroid function dropped to 50% while subclinical hypothyroidism remained stable at 23.3% and now 26.7% demonstrated progression to clinical hypothyroidism.

Conclusion: There is a high risk of radiation-induced thyroid dysfunction, particularly clinical hypothyroidism, in head and neck cancer patients receiving radiotherapy.