The Effect Of Equivalent Uniform Dose Optimization Method On Protection Of Parotid Gland In The Radiotherapy Of Nasopharyngeal Carcinoma

[Objectives]To explore the clinical significance of Equivalent uniform dose(EUD)optimization method on plan optimization of IMRT in nasopharyngeal carcinoma(NPC).To compare the differences in protection of organ at risk(OARs)and volume of target between EUD biological optimization method and conventional dose-volume(DV)physical optimization method.[Methods]20 patients of NPC with pathological diagnosis were selected from Kunming General Hospital,between September 2014 to October 2016.The clinical target volume of NPC were delineated by well-trained doctors according to the consensus standard.Two sets of plans were formulated for each patiente,classified as control group and experimental group.The plans in control group were based on dose-volume physical optimization method,while EUD constraint of parotid gland was used in experiment group.The differences of V26,Dmean and NTCP of parotid gland were assessed between the two groups.Furthermore,the differences of target volume,TCP and Dmax of OARs were also analyzed.[Results]1.Effects on parotid gland:V26 of parotid gland in biological optimization group was 51.90±7.86%,which was significantly decreased compared to that in physical optimization(P<0.05).Mean dose of parotid gland was 30.52±3.53Gy in biological optimization,which was 33.44±3.68Gy in physical optimization.There was a significant difference between the two groups(P<0.05).NTCP of parotid gland was 17.73±6.89%in biological optimization group,which was obviously reduced compared with the physical optimization group.2.Effects on target volume and TCP:The target volumes of VPGTVnx(70.4)in biological optimization and physical optimization group were 99.53±0.39%and 99.63±0.50%,respectively.The differences between the two groups were not significant(P>0.05).The target volumes of VPGTVnd(66)was 99.38±0.69%in biological optimization group,which was 99.56±0.52%in physical optimization group.The differences between the two groups were not significant(P>0.05).TCP was 96.29±2.22%in biological optimization group,which was 96.28±2.22%in physical optimization group.The differences between the two groups were not significant(P>0.05).3.Effects on Dmax of spinal cord,brain stem,and optical chiasma:The Dmax of spinal cord,brain stem,and optical chiasma in biological optimization group were 42.57± 1.91Gy,52.97±1.97Gy,and 47.58±5.19Gy,respectively.While the Dmax of them were 42.47±2.00Gy,53.01 ± 1.67Gy,and 47.57±5.06Gy,respectively.The differences between the two groups were not significant(P>0.05).[Conclusions]EUD optimization of parotid gland could significantly reduce the V26,Dmean,and NTCP in parotid gland compared to conventional DV physical optimization method.After EUD optimization,the irradiated volume and exposed dose of parotid gland is decreased.Meanwhile,the target volume(VPGTVnx,VPGTVnd)and TCP are not significantly affected.EUD optimization could overcome the dose limits of OARs,which could ensure clinical efficacy of radiotherapy.