| Objection: The goal of this study was to evaluate the effect of positional changes and volumetric of parotid gland(PG) for dosimetric in nasopharyngeal carcinoma(NPC) treated with intensity-modulated radiotherapy(IMRT).Methods: Between September 2011 and July 2014, 39 patients with NPC were enrolled in this study. All patients have two sets of CT images. There were 30 male and 20 female. The range of age was from 21 years old to 71 years old. The median age was 40 years old. Of the patients, 4 were in pathologic Stage II disease, 19 were in Stage III, and 16 were in Stage IV. The first and second CT images were fused in the Pinnacle system. Then parotid glands contour and body contour were mapped to the first CT images and imported the first radiotherapy plan,and the dose、the volume and the centroid of parotid glands, DSC and △V(%) of parotid glands and GTVnx volume were computed. Evaluating the effect of the position changes and the volumetric of parotid gland for dosimetric by paired-samples t-test and two-tailed Spearman correlation.Result: The mean volume of the left and right of parotid glands before radiotherapy were(23.85±9.46)cm3 and(23.90±9.11)cm3,respectively. The mean volume of the left and right of parotid glands at end of radiotherapy was(17.13±7.26)cm3and(16.76±6.34)cm3, respectively. The results of paired-sample t-test of the left and right parotid glands were 8.65(P=0.00)和 8.67(P=0.00),respectively. The changes in Dmean 、D50、V26 of left parotid gland were 13.88±24.36%、7.66±21.78%、7.48±15.98%, respectively. And the right parotid gland were 11.31±15.24% 、 17.82±24.92% 、12.67±20.56%. There was significant increase of the dose. There was no significant correlation between the dosimetric of the left and the right parotid gland. The changeof GTVnx volume was(71.69±18.51)%. the mean DSC value of the left and right parotid gland were(0.62±0.13)and(0.59±0.15), respectively. the mean displacement distance of the centroid of the left and right parotid gland were 0.51±0.19 cm and 0.56±0.22 cm, respectively. Of the left parotid gland, there were 30 moved to inside, 8 moved to outside and 1 didn’t move. Of the right parotid gland, there were 31 moved to inside, 7 moved to outside and 1 didn’t move. There was significant correlation between the changes in dose of parotid glands and the change in position of parotid glands(Spearman’s correlation coefficient: left:-0.57,-0.58 and-0.58,(P<0.01); right:-0.63,-0.67 and-0.60,(P<0.01)). There was significant correlation between the changes in dose of parotid glands and the change in position of parotid glands.There was not significant correlation between the dosimetric of parotid glands and the displacement distance of parotid gland centroid(P=0.000). The change in dose of parotid gland was not associated with the change in volume of GTVnx(P>0.05).Conclusion: The change in dose of bilateral parotid glands, parotid gland volume and position were significant. The positional change of parotid gland is the most important factor for the dosimetric of parotid gland. |
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