RESUMO
Objective To investigate the setup error for nasopharyngeal carcinoma (NPC) patients with poor compliance using kV cone-beam computed tomography,and to calculate the expansion margin from the clinical target volume (CTV) to planning target volume (PTV).Methods In 45 NPC patients from 2013 to 2015,the setup error,95％ confidence interval (CI)-1 for random error,and PTV-1 value were calculated.Moreover,in 16 NPC patients with poor compliance based on five verifications (random error not within 95％ CI-1),the setup error,95％ CI-2 for random error,and PTV-2 value were calculated.For the 16 special patients,PTV-1 and PTV-1 combined with PTV-2 were used to develop the plan-1 and plan-2,respectively.The dosimetric difference between plan-1 and plan-2 was evaluated.Results Both PTV-1 and PTV-2 had the largest expansion margin in the y direction.The CTV of plan-1 could not meet the requirement of the prescription dose after the setup error was introduced.Compared with plan-1,the V95％ and D95 values for the CTV of plan-2 were increased by 6.26％ and 4.43％,respectively.The D01 value was significantly larger in plan-2 than in plan-1 (P=0.005),which,however,met the clinical requirement.Conclusions In patients with poor compliance,the dose to target volume can be effectively elevated and the normal tissue can be spared from damage when PTV-1 combined with PTV-2 is selected as expansion margin.
RESUMO
Objective To compare the 7th edition of International Union Against Cancer ( UICC) staging system with the Chinese 2008 staging system for nasopharyngeal carcinoma ( NPC) , and to provide evidence for further updating of the staging system. Methods A retrospective analysis was performed among 767 patients who were pathologically and newly diagnosed with non?metastatic NPC and treated with intensity?modulated radiotherapy from 2006 to 2012. Based on the main prognostic indices, overall survival ( OS) , locoregional failure?free survival( LFFS) local relapse?free survival ( LRFS) , and distant metastasis?free survival ( DMFS) rates, the value of T stage, N stage, and clinical stage in prognostic prediction was compared between the two staging systems. The Kaplan?Meier method was used for calculating survival rates. The log?rank test was used for survival difference analysis. The Cox model was used for multivariate prognostic analysis. Results In terms of T stage, the Chinese 2008 staging system was a significantly better predictor of the OS and LRFS rates than the 7th edition of UICC staging system. In terms of N stage, they were comparable in the prediction of the OS and DMFS rates. In terms of clinical stage, the 7th edition of UICC staging system was a significantly better predictor of the OS rate than the Chinese 2008 staging system. For the new staging system proposed based on the statistical results, the T, N, and clinical staging gave significantly better prognostic prediction. Conclusions The 7th edition of UICC staging system and the Chinese 2008 staging system for NPC have their own advantages in prognostic prediction. The new staging system proposed in this study could contribute to the updating of the current staging system for NPC.
