A Study On Target Mobility Rule And Dosimetry Of Primary Middle And Distal Esophageal Cancer During The Radiotherapy

Objective: To investigate the target movement rule of the differentsegments of esophageal cancer on the three dimensional direction in theintrafractionated reditherapy.And analysis the variation of respiratorymotion and target mobility for esophageal cancer and normal tissueaffected by the radiation dose distribution.Methods: This study had collected30patients of esophageal squamouscarcinoma, who were previously untreated.The primary middleesophageal patients had15and the distal esophageal cancer patients have15.27cases of men and3cases of women in these patients,the medianage of which was63.Two cases was in T2staging,16and12cases wererespectively in T3/T4staging. The patients underwent4D-CT simulationscan and were collected the CT images of the ten respiratory phasesduring free breathing. The tumor volume (GTV)were respectivelydelineated on CT images of the ten respiratory phases and measured itscentre point position coordinates to determine the range of tumor motionin the different direction of the right and left sides (RL),theanterior–posterior sides(AP) and the superior–inferior sides(SI). ANDThe external margin of GTV in the phase0%versus50%wasconventionally enlarged to get CTV0CTV5, and PTV0、PTV5. Plan1 was designed according to the prescription dose(6600cGY/33f) in theimage of the phase0%CT and transported completely to the image of thePhase50%CT to make a Plan2. The tumor target and the surroundingnormal tissue irradiated dose under the two states in the process ofbreathing were compared in the Plan1and Plan2. The target andsurrounding normal tissue irradiated dose were compared in the basis ofthe Plan1and Plan2. Statistical analyses were performed by One-WayANOVA analysis in the group. Comparison between groups was used bypaired t-test. And pearson correlation analysis method was included in thestatistical analyses. The relationship between target motion and stage wasmade by the Mann-Whitney U rank. Application of SPSS20.0statisticalsoftware package for analysis, P <0.05for the difference was statisticallysignificant.Results:(1) The peak to peak displacement of the centroid of the middlethoracic GTV in the RL, AP, SI direction was respectively0.22±0.090cm,0.20±0.080cm,0.38±0.095cm. The displacement of thelower thoracic GTV mobility was respectively0.25±0.087cm,0.26±0.089cm,0.56±0.134cm.The displacement of the three-dimensionaldirection for the middle thoracic GTV and the lower thoracic GTVmobility was statistically significant difference (F=17.323, P=0.000, F=40.719, P=0.000). The displacement of the centroid of the middlethoracic GTV and the lower thoracic GTV mobility in the AP、SI direction was statistically difference,(t=-2.049,-4.360, P=0.049,0.000)in the AP and SI direction.(2) The Peak displacement of the middlethoracic GTV and the lower thoracic GTV were significant correlatedwell with respiratory movement displacement(P <0.05).There was onlycorrelation between the lower thoracic GTV mobility and heart beatdisplacement in SI direction, r=0.558、P=0.031. There was significantcorrelated with in the the lower thoracic GTV and the left and right sidesof the dome of diaphragm, r=0.524、0.670，P=0.045、0.006.The rightsides of the dome of diaphragm was correlated with in the the lowerthoracic GTV in RL direction, r=0.584、P=0.022.(3) Changes in themiddle thoracic GTV and the lower thoracic GTV volume showed anegative correlation with the double lung(r=-0.887、-0.927，P=0.001、0.000and r=-0.803、-0.945，P=0.005、0.000),but the correlation was notsignificant with the heart during respiratory cycle.(4) In three dimensionaldirections,T3stage thoracic segment esophageal dynamic degrees weregreater than the T4stage GTV mobility, difference was statisticalsignificance (Z=2.055,2.336,2.336, P=0.040,0.020,0.014).(5)Analysis of the dosimetric evaluation of the middle thoracic and thelower thoracic GTV under two limit Phases in the free-breathing state:For PTV,The Dmin、D100、D98、D95、D90、V95%、V90%averages ofthe Planl were higher than Plan2for the middle thoracic and the lowerthoracic target volume, the difference was statistically significant (P<0.05). For PTV, the HI values of the Planl was less than Plan2for themiddle thoracic and the lower thoracic target volume（P=0.027）,this wasthat dose distribution of Plan1was uniformity better than Plan2.For CTV,the Dmin、D100averages of the Planl has a statistically significantdifference with Plan2(P=0.016、0.011). The remaining parameter indexwas no significant difference between the two Plans. Analysis ofexposure doses of the spinal cord, lungs and heart showed no statisticallysignificant difference in all kinds of indicators for the two Plans.Conclusions:1. The mobility of the middle thoracic and the lower thoracic GTV wasconsidered statistically significant in the three dimensional directionsunder the respiratory control technology. The ITV margins of0.3cmRL,0.30cm AP,0.5cm SI would accound for95%of respiratory GTVmotion were covered in the middle thoracic esophageal cancer, and theITV margins of0.3cm RL,0.40cm AP,0.7cm SI would accound for95%of respiratory GTV motion were covered in the lower thoracic esophagealcancer2.This study show that respiratory motion was still a major factor toaffect the movement of thoracic esophageal cancer, and The movement ofthe heart beating was the secondary factor, The staging may be anotherimportant factor to affect the thoracic esophageal target movement andthe stage of esophageal cancer target was more later, the mobile degree was smaller.3. The exposure doses of the middle thoracic and the lower thoracic targetvolume under two limit phases in the free-breathing state had existeddifferences. For PTV, the D100、D98、D95averages of the Planl werehigher than Plan2. For CTV, the D100averages of the Plan1was higherthan Plan2.The respiratory movement and the target motion forintrafractional radiotherapy make tumor dose inadequate, which wasprobably one of the reasons for local recurrence after radiotherapy.