Early Assessment Of Radiation-Induced Parotid Damage Using T2~* Mapping And Tlrho-Weighted Magnetic Resonance Imaging

Part ?:Early assessment of radiation-induced parotid damage using T2*mappingObjective:Radiation-induced parotid damage is a common complication of radiotherapy in patients with nasopharyngeal carcinoma(NPC),which has been associated with xerostomia,dysphagia,dental decay and even sleep disorders,severely reducing their life quality.The objective of this study was to investigate the value of T2*mapping for monitoring the dynamic changes of parotid glands during radiotherapy in patients with NPC.Methods:Thirty-four patients with NPC were prospectively enrolled in this study.All patients underwent T1-and T2-weighted imaging,and T2*mapping for bilateral parotid glands at pre-RT(within 2 weeks before radiotherapy),mid-RT(5 weeks after the beginning of radiotherapy)and post-RT(4 weeks after the completion of radiotherapy).Parotid magnetic resonance(MR)parameters,mean radiation dose,and xerostomia degrees were recorded.The dynamic changes and correlations of parotid MR parameters were analyzed.Furthermore,nine healthy volunteers undergone T2*mapping with an interval of 4 weeks were enrolled for reproducibility study of T2*value.Results:From pre-to mid-and post-RT,parotid volume(atrophy rates,25.34� 11.33%and 25.74 � 9.93%,respectively)and T2*value decreased(change rates,-5.63�8.86%and-4.81 � 10.67%,respectively)significantly(all P<0.01).Parotid normalized T1 signal intensity decreased significantly from pre-to post-RT(change rate,-7.43�10.61%,P=0.007),and its change rate correlated inversely with mean radiation dose significantly(r=-0.646,P<0.001).Parotid volume,T2*value and xerostomia degree showed corresponding change pattern during radiotherapy.All parotid MR parameters showed excellent reproducibility(intraclass correlation coefficient,0.843-0.993).Conclusion:Radiation-induced parotid damage in patients with NPC could be noninvasively evaluated by conventional MR imaging and T2*mapping.Part ?:Early assessment of radiation-induced parotid damage using Tlrho-weighted magnetic resonance imaging Objective To investigate the feasibility of Tlrho-weighted MR imaging to evaluate the dynamic changes of parotid glands in patients with nasopharyngeal carcinoma(NPC)undergoing intensity-modulated radiotherapy(IMRT).Methods:Twenty-six NPC patients(19 men,7 women;age,48.9� 13.4 years)were prospectively enrolled,and underwent the following three serial Tlrho-weighted MR imaging:pre-RT(within 2 weeks before radiotherapy),mid-RT(5 weeks after the beginning of radiotherapy)and post-RT(4 weeks after radiotherapy).Parotid volumes,Tlrho values,mean radiation doses,and xerostomia degrees of the patients were recorded.Change rates of parotid Tlrho values during radiotherapy were correlated with parotid atrophy rates,mean radiation doses and xerostomia degrees of the patients.Results:During radiotherapy,parotid volume decreased(atrophy rate,32.7 � 8.1%at mid-RT and 27.9� 10.0%at post-RT compared to pre-RT;both P<0.001),and parotid Tlrho values increased(change rate,25.0 � 15.8%at mid-RT and 30.1 � 18.0%at post-RT compared with pre-RT,both P<0.001)significantly.The change rate of parotid Tlrho value correlated with the atrophy rate significantly at post-RT(r=0.301;P=0.047).Intra-and inter-observer reproducibility of parotid Tlrho measurements were excellent(intraclass correlation coefficient,0.974 and 0.956,respectively).Conclusion:Dynamic changes of radiation-induced parotid damage in patients with NPC who underwent IMRT could be noninvasively evaluated by Tlrho-weighted MR imaging.