Function protection of the parotid gland after intensity modulated radiotherapy for thirty-six patients of nasopharyngeal carcinoma

Objective: To study the parotid gland function protection of intensity modulated radiotherapy (IMRT) for patients with nasopharyngeal carcinoma (NPC) Methods: Thirty-six NPC patients were divided into IMRT group (therapy group) and conventional fraction (CF) group (control group) by random balanced design. Each group had 18 patients. The planning gross tumor volume (pGTV) of nasopharyngeal was treated with a total dose of 72.0 in therapy group, with a total dose of 70.0 Gy in control group (with daily 2.0 Gy/fraction and 5 times/week). Before treatment and at 3, 6, and 9 months, 1 and 2 years after therapy, all patients performed parotid imaging and both uptake index (UI) and excretion index (EI) after acid stimulation were calculated. The dose-volume histogram (DVH) was used to analyse the dose of parotid. Results: The values of UI were 77.6% and 96.2% at the end of therapy and after tow years in therapy group and 56.8% and 7.0% in contrast group. The values of EI were 64.1% and 95.3% at the end of therapy and after tow years in therapy group and 19.4% and 0 in control group. The mean doses of normal side and the trouble side of parotid gland were 20.0 Gy and 31.0 Gy in therapy group and 61.0 Gy and 68.2 Gy in control group. Conclusions: IMRT can reduce radiation dose of parotid glands compared with CF distinctly and thus protect parotid function effectively. (authors)