The Clinical Significance Of The Change Of The Normal Organs Volume And Dose In IMRT For Nasopharyngeal Carcinoma

Objective: To investigate the change of the normal organs volume and dose in intensity modulated radiotherapy for nasopharyngeal carcinoma through repeat CT imaging and replanning.Methods: This study enrolled twenty patients with nasopharyngeal carcinoma 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 rebuilded with the same body position and reference coordinate at the twentieth time during radiotherapy, the plan1 was copied to the second CT-simulated image and generated plan1-2 and DVH1-2, redesigned the second CT-simulated image and formed plan2, The data obtained with CT-simulated image and DVH were analyzed the normal organs volume and dose variations between before and the twentieth treatment.Results: The volume of plan1-2 about the left and right parotids were much less compared with plan1(P<0.05), The maximum dose,mean dose,D50 and V35 of parotid glands and the maximum dose,mean dose and D1cc of spinal cord increased obviously(P<0.05), There was statistical significance on the maximum dose of brain stem(P=0.011),the parotids'dose augmented 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 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.