Discussion
cancers, memory loss, head and neck tumors, fatigue, mucous oedema, NPC, toxicities, head and neck cancers, long-term sequelae, constipation, coma, oropharynx and hypopharynx cancers, HT, hypothyroidism
ORAL CAVITY TUMOR, CANCERS, NASOPHARYNGEAL CARCINOMA, LARYNGEAL CANCER, COMA, HEAD AND NECK CANCER, HYPOTHYROIDISM, SUBCLINICAL HYPOTHYROIDISM
With the widespread use of intensity-modulated radiation therapy (IMRT) in recent decades, most patients with nasopharyngeal carcinoma (NPC) are now able to survive long-term. However, NPC survivors still face a number of long-term sequelae that have many negative effects on their quality of life. One of the most common late toxicities is hypothyroidism (HT). It is reported to occur in 40–50% of patients treated with neck irradiation [A single center randomized clinical trial was completed to determine whether V40 ≤ 85% can be used as an effective dose constraint in IMRT planning. The cumulative incidence of subclinical HT in patients was 20%, 31%, and 37% at 1, 2, and 3 years, respectively. A total of 28 patients (30.4%) developed subclinical HT, similar to previous study [In our study, consistent with a previous study by Sommat et al. [Our study indicated the importance of regular follow-up as well as testing of thyroid function in NPC patients after radiotherapy. Usually, Patients with subclinical hypothyroidism occurs insidiously and lack specific symptoms. Symptoms in patients with subclinical hypothyroidism are mainly characterized by reduced metabolic rate and decreased sympathetic excitability, such as fatigue, memory loss, constipation, and slow pulse rate. Rarely, coma with mucous oedema occurs in patient with severe subclinical hypothyroidism. Furthermore, according to the guideline about subclinical hypothyroidism [The overall survival rate for patients with NPC is higher than for other head and neck tumors, which means that quality of survival associated with hypothyroidism draws the attention for NPC patients after radiotherapy. Therefore, it is important to explore whether thyroid V40 ≤ 85% can be used as an effective dose constraint in IMRT planning. However, the outcomes cannot be extrapolated to other entities where the neck receives bilateral irradiation, such as oral cavity tumors, oropharynx and hypopharynx cancers. As the planning target volume of other neck cancers usually include a portion of the VI lymph nodes, the actual irradiation dose to the thyroid gland in patients with other neck cancers is higher than NPC patients. Moreover, the dose of irradiation of the drainage area of the cervical lymph nodes in patients with other neck cancers, such as laryngeal cancer, is different from that of NPC patients. Therefore, to ensure the efficacy of treatment for other head and neck cancers, the thyroid should not be unduly restricted.The main strength of our study is that it is the first randomized clinical trial that explored the HT induced by radiotherapy in NPC in a follow-up period of 34 months. However, limitations of the study also need to be considered. First, this is a single-center study with a small sample size. The recommended samples were taken as per sample size calculation to provide adequate power to detect significance. However, larger, multi-center randomized clinical trials are needed to generalize the result. Second, this study did not evaluate the quality of life of patients. Further study will be conducted in the future.