DVH analysis of the change of normal organs volume and dose in intensity modulated radiotherapy for nasopharyngeal carcinoma

Objective:To study the change of the normal organs volume and dose in intensity modulated radiotherapy for nasopharyngeal carcinoma with dose-volume histogram(DVH).Methods:Twenty patients with nasopharyngeal carcinoma were treated by intensity modulated radiotherapy(IMRT),CT-simulated image was rebuilded with the same body position and reference coordinate at the twentieth time during radiotherapy.The data obtained with DVH were analyzed on the normal organs(eyeballs,bilateral lens,optic nerves,parotid glands,spinal cord and brain stem) during, before and the twentieth treatment.Results:The volume of DVH2 about the left and right parotids were much less compared with DVH1(P0.05).The maximum and mean dose of parotid glands and spinal cord increased obviously,there was statistical significance on the maximum dose of brain stem(P=0.011),the parotids' dose augmented correlated with the shrunken degree of parotids,and other normal organs had no difference.Conclusion:There were some changes of the normal organs volume and dose in IMRT for nasopharyngeal carcinoma,especially for parotid glands.It was requisite to rebuild CT-simulated image and renew plan during midanaphase treatment to reduce radiate dosage and avoid radiotherapy reaction.