Changes of volume dose of normal organs in IMRT for nasopharyngeal carcinoma

Objective To investigate the changes of the volume dose of normal organs in intensity modulated radiotherapy for nasopharyngeal carcinoma through repeated CT imaging and replanning.Methods This study enrolled twenty patients with nasopharyngeal carcinoma who were treated by intensity modulated radiotherapy(IMRT) as the first-line treatment,nasopharynx,cervical part and supraclavicular region were all treated by IMRT;we designed the first IMRT plan(plan1)and formed DVH1.CT-simulated image was rebuilt at the same body position at the twentieth time during radiotherapy,and plan1 was copied to the second CT-simulated image and generated plan1-2 and DVH1-2.we redesigned the second CT-simulated image and formed plan2,The data obtained from CT-simulated image and DVH were analyzed terms of in the vanations of normal organ volume dose between before and the twentieth treatment.Results The volume of plan1-2 about the left and right parotids were much decreased compared with plan1(P0.05).The maximum dose,mean dose,D50 and V35 of parotid glands,the maximum dose,mean dose and Dlcc of spinal cord obviously increased(P0.05).There was statistical difference in the maximum dose of brain stem(P=0.011);the parotid′s augmented dose correlated with the shrunken degree of weight,left and right contour and parotids;and the maximum dose of spinal cord correlated with left and right contour(r=0.469,P=0.037);and other normal organs have no difference.Conclusion There were some changes of the normal organs volume 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 radiated dosage and avoid radiotherapy reaction.