Relationship between the parotid glands function and the dose-volume effect in nasopharyngeal carcinoma patients with intensity-modulated radiotherapy by radionuclide imaging

Objective To evaluate the parotid glands function and the dose-volume effect in nasopharyngeal carcinoma (NPC) patients with intensity-modulated radiation therapy (IMRT) by radionuclide imaging. Methods From July 2005 to July 2006,the excretion index (EI) and uptake index (UI)of parotids in 33 NPC patients with radical IMRT was examined by radionuclide imaging,prior to IMRT,and at median dose,at the end of radiotherapy,and the follow-up time after radiotherapy. The relationship between parotid function (EI and UI)and DVH were analyzed. Results Scintigraphy showed that the EI of parotid were 0.58±0.13,0.17±0.22,0.09±0.17,0.42±0.18 at the beginning,the median dose,the end,and the follow-up time,respectively (P=0.000). EI decreased significantly after median and total doses as compared to that of pretherapy,and to the lowest level at the end of radiotherapy. During the follow-up time period,a recovery of EI was observed over time. EI were 0.30±0.21 at less than 6 months,and 0.53±0.12 at more than 6 months after IMRT (P=0.002). UI were 5.05±2.28,5.78±2.41,5.38±2.10 and 4.52±2.25 at the same intervals (P=0.070).The DVH showed that the mean dose of parotid was 35.5 Gy for all patients. During the follow-up time,the EI were 0.51±0.10,0.37±0.14 at mean dose of parotid ≤median group [mean dose of parotid:(32.88±1.66)Gy] and median group [mean dose of parotid:(38.13±2.05)Gy] (P=0.007). EI of V26≤median group [mean V26:(62.5±4.4)%],V26median group [mean V26:(80.1±8.1)%] were 0.49±0.12、0.40±0.14 (P=0.086) at the same follow up time. There was no significant difierence in UI between the two groups (P0.05). According to the RTOG criteria of xerostomia,85% of the patients had Grade 2,15% had Grade 1 at the moment after IMRT. The average follow-up time was 17 months (ranging 10 to 22 months),only 12% had Grade 2,70% had Grade 1,and 18% had Grade 0. There was one patient with local recurrence at nasopharynx and neck,three patients developed distant metastases,one of these patients died. Conclusions EI of parotid decreases significantly after IMRT,but increases during the follow-up over time although mean dose of parotid is 35.5 Gy. It way contribute to the improvement of EI if the dose of irradiation to the parotid is reduced.