Assessment of radiation-induced salivary gland change in nasopharyngeal carcinoma: Correlation between clinical xerostomia grade and contrast-enhanced CT density change

Abstract

Background : Radiation-induced xerostomia is the most common complication in patients with nasopharyngeal carcinoma (NPC) after radiation therapy (RT).

Objective : To correlate salivary dysfunction as assessed by clinical xerostomia grade with change in computed tomography (CT) density of the salivary glands on contrast-enhanced CT in patients with NPC treated with RT.

Methods : Seventeen patients with NPC, who had contrast-enhanced CT before and after radiation therapy            (70 - 75 Gy) were assessed retrospectively. CT density change was calculated using difference in attenuation            (Δ attenuation) and ratio of attenuation (Δ ratio). The ratio of attenuation was: parotid or submandibular attenuation (HUs) / ipsilateral paraspinal muscle attenuation (HUs). The mean Δ ratio of bilateral parotid glands and submandibular glands in each patient was statistically correlated with clinical xerostomia grade. Mean percentage change in attenuation and ratio for all salivary glands were used as a CT index and ratio index and compared with clinical xerostomia grade.

Results : Attenuation (HUs) and ratio of attenuation in the parotid and submandibular glands after radiation significantly increased from pre-radiation (P <0.001). There was no significant correlation between Δ ratio and clinical xerostomia grade in parotid and submandibular glands at any of the 3 follow-up points. There was no significant difference between CT index and ratio index among the xerostomia grade 0, grade 1, and grade 2 groups.

Conclusions : Contrast-enhanced CT can detect increase in attenuation of the parotid and submandibular glands in NPC treated with RT, but there was no significant correlation between CT density change and severity of clinical
xerostomia grade.