Simulafion of respiratory motion effect on dose distributions in three-dimensional radiotherapy of tumor

Objective To evaluate the effects of respiratory on dose distributions in three dimensional conformal radiotherapy (3 DCRT) and intensity-modulated radiotherapy (IMRT).Methods The dose distributions were measured with a Sun Nuclear Mapcheck 2D-ARRAY placed on a moving platform home-made to simulate the respiratory.The periodic motion of the moving platform was 3.5 s.The rang of the moving platform was ± 3 mm,±5 mm,± 10 mm,± 15 mm.Dosimetric comparisions for 3DCRT and IMRT plans were performed by means of Gamma analysis with 3％ and 3 mm,respectively.Dates of two groups were used by paired t-test.Results The respiratory could reduce the target dose and conformal index,blurring effect of dose distribution.The pass rate (3％/3 mm) in 3DCRT was greater than it in IMRT of the 11 cases,and P ＜ 0.05 ; The failed points were mainly near the field edge for 3 DCRT plans,but located in the whole target volumes for IMRT plans.Conclusions Respiratory motion blurred the dose distribution of 3DCRT and IMRT,yet the influence on IMRT was much more striking.As for tumors with large motion amplitude,it is advisable to use 3DCRT rather than IMRT techniques.3DCRT may deliver a more reliable dose distribution by cautiously delineating the PTV margin. Key words: Respiratory motion;  Three-dimensional conformal radiotherapy;  Intensity-modulated radiotherapy;  Dose distribution