Abstract:

Objective To explore the effect of different calculation grids in the treatment planning system(TPS) on the dose distribution for the target and recepted doses of organs at risk (OAR) and to provide basis for clinical treatment.
Methods Ten nasopharyngeal carcinoma patients  recepted fixed-field IMRT rediation therapy were treated with  Anisotropic Analytical Algorithm(3A) method.Calculation grid of 2.50 mm was selected as control group and calculation grids of 5.00,4.00,3.00,2.00,1.00 and 1.25 mm were selected as experiment groups to perform  6 treatment plans.Pencil Beam Convolution (PBC) Algorithm were used for calculation,calculation grid of 2.50 mm was selected as  control group and calculation grids of 10.00,5.00 and 1.25 mm were selected as experiment groups to perfrom  4 treatment plans respectively for 10 patients.The effects of different calculation grids on the maximum dose,the minimum dose,the mean dose,conformal index and homogeneity index of the target,and the maximum dose of brain stem,left lens,left optic nerve,optic chiasm and spinal cord were analyzed by dose volume histogram.Results Compared with control group,with  3A method,the  size calculation grid was increased,the  maximum dose,the mean dose and conformal index of the target were increased;but the  homogeneity index, the maximum dose of the target,and the  maximum dose of left len were decreased（P<0.05）.With PBC  Algorithm,the  size calculation grid,the  the maximum dose,the minimum dose,the mean dose and conformal index of the target were increased;but the  homogeneity index of the target,and  the  maximum doses of left len and spinal cord were decreased,and the maximum dose of optic chiasm was increased（P<0.05）.Conclusion The target dose distribution and the dose of OAR change with the changes of  calculation grids.Using the right size calculation grid can evaluate  accurately the  doses of   the target and OAR.In clinical use,the calculation grid should generally choose 2.5-5.0 mm,and the  recommended grid is  2.5 mm.
 

Key words: calculation grid;treatment plan system;dose