Ultrasound evaluation of salivary and thyroid glands in patients treated with external beam radiotherapy for nasopharyngeal carcinoma

Abstract

Radiation-induced xerostomia and hypothyroidism from damaged salivary and thyroid glands respectively are the common complications in head and neck cancer patients treated with external beam radiotherapy (RT). Ultrasound is a common imaging tool in the assessment of salivary and thyroid glands, which should be useful in investigating their post-RT morphological changes aiding differential diagnosis of the glands. In the present study, the sonographic appearances of salivary and thyroid glands in nasopharyngeal carcinoma (NPC) patients treated with different RT techniques were investigated and compared. In the investigation of parotid glands, 43 NPC patients treated with conventional RT, 38 NPC patients treated with intensity-modulated radiotherapy (IMRT) and 58 healthy subjects were involved. Parotid glands were sonographically assessed for their size, echogenicity and internal architectures. The mean transverse dimension of parotid glands in patients treated with conventional RT and those treated with IMRT were significantly smaller than that in healthy subjects (p < 0.05). Parotid glands of the IMRT group tended to be hyperechoic, homogenous, without hypoechoic areas and with marginally-seen intra-parotid ducts, which are similar to the findings in healthy subjects. Parotid glands in the conventional RT group tended to be hypoechoic, heterogeneous, with hypoechoic areas and had obviously-seen intra-parotid ducts For the submandibular glands, a total of 81 NPC patients treated with external beam radiotherapy and 66 healthy subjects were recruited and had a submandibular gland ultrasound examination. Bilateral submandibular glands were sonographically assessed for their size, echogenicity, border sharpness and internal architectures. The mean transverse dimension of submandibular glands in patients treated with RT was significantly smaller than that of the healthy subjects (p < 0.05). Submandibular glands in patients treated with RT tended to be heterogeneous with hypoechoic areas and ill-defined borders, whereas submandibular glands in healthy subjects usually appeared homogeneous without hypoechoic areas and had well-defined borders. However, there were no significant differences in echogenicity and conspicuity of intra-glandular ducts of submandibular glands between patients and healthy subjects (p > 0.05), in which the glands in both study groups tended to be hyperechoic and with marginally seen intra-glandular ducts. In the investigation of thyroid glands, 103 NPC patients who had finished radiotherapy of cervical lymph nodes using anterior cervical field, 30 NPC patients who had finished radiotherapy of cervical lymph nodes using IMRT and 61 healthy subjects were involved. Thyroid glands were sonographically assessed for their size, echogenicity, vascularity and internal architectures. Thyroid function test was also performed on each subject/patient. Compared to the patients with abnormal thyroid function, thyroid glands of the patients with normal thyroid function tended to be homogenous, and greater in thyroid volume and echogenicity index (p < 0.05). However, there were no significant differences in vascularity index, incidence and number of nodules, and echogenicity of thyroid glands between the two patient groups (p > 0.05). On the other hand, compared with the healthy subjects, the thyroid glands of patients treated with IMRT and those treated with anterior cervical field showed significantly lower thyroid volume, lower incidence and number of nodules, and higher vascularity index (p < 0.05). However, there were no significant differences in the thyroid echogenicity and echogeneity (p > 0.05). Ultrasound is a useful imaging tool in the evaluation of radiation-induced changes of salivary and thyroid glands in NPC patients with previous radiotherapy. For more accurate detection and to prevent misdiagnosis, the sonographic appearances of post-RT salivary and thyroid glands should be noted in ultrasound examination of patients with previous radiotherapy for NPC or other head and neck neoplasms.