Displacement Of Pulmonary Tumors With The Change Of Respiratory Patterns In Radiotherapy

?Background? To evaluate the displacement and motion of pulmonary tumors with the change of respiratory patterns in radiotherapy by 4DCBCT.?Materials and methods?25 4DCT images and 125 CBCT images were collected from 25 patients.Image matching between the 4DCBCT and the planning CT was carried out by using dual registration(Clipbox and Mask).The change of respiratory patterns was defined as the change of the ratio of time spent in inspiration(I)versus time spent in expiration(E)(I=E ratio)in each CBCT image and we used D-value between extrema in Mask to indicate the displacement of tumors.?Results?With the progression of treatment,the mean I/E ratio was 1.1 + 0.12,and the change was related to the treatment fraction and different patients(F=3.89,P=0.00),time weight: I =52%±3%,E=47%±3%.Displacement of tumors was AP:0.2cm,SI:0.39 cm,RL:0.19 cm.And the deviation in SI had statistical significance(F=2.07,P=0.04).The motion of lung with respiratory patterns was the same as the motion of tumors: motion in SI direction is always larger than those in LR direction and AP direction.There was no evidence showed the relationship between the motion and radiotherapy fractions reached statistical significance(F=0.498,P=0.79).Yet we found the size of tumors(r=0.72,P=0.000)and the location of tumors(r=0.36,P=0.018)mattered.?Conclusions?Real-time 4DCBCT guided radiotherapy is suitable for those patients who take giant breaths and who have considerable tumor motions.The change of respiratory patterns affect the ITV so effectively that physicists should design plans based on the patterns.