| Objective:By comparing and analyzing the influence of different grid size parameter settings on different sites of plans when using the Monaco5.11 treatment planning system to make volume modulated arc stereotactic radiotherapy plans.This paper provided a reference for the selection of grid size parameter in clinical plan design.Method:Thirty patients undergoing stereotactic radiotherapy were selected,10 cases each of head,chest and abdomen.With 2.5 mm grid,volumetric modulated arc technology was used to design stereotactic plans in Monaco5.11 treatment planning system,then plan results were recalculated with MC algorithm using 1 mm,2 mm,3 mm,4 mm,5 mm grid,each case received six plans for a total of 180 plans.To 1 mm grid group for comparison,comparing the differences in plan quality and plan efficiency between plans with different grid size paramenters in the same site and between plans in different sites.The plan quality indicators included the dosimetric parameters of the target and organs at risk,the plan efficiency indicators included computing time,monitor units and treatment time.Three-dimensional dose verification was performed to measure the gamma pass rate of these plans to compare their differences in calculation accuracy.Results:1.As the grid size increased,the D2%and D50%of the target in the three sites plans become larger,and D98%beome smaller;HI and GI become larger,and CI become smaller.Compared with the 1mm group,the maximum percentage difference in head cases:D2%was 2.7%,D50%was 2.5%,D98%was 2.4%,in chest cases:D2%was 1.8%,D50%was 1.2%.D98%was 0.8%,in abdomen cases:D2%was 1.9%,D50%was 2%,D98%was 0.7%,and the differences were statistically significant(P<0.05).2.In head cases,Dmean of left and right eyeballs and brainstem,Dmean and V12 of normal brain tissue increased with the increase of the grid size,and the difference between each group and the 1mm group was statistically significant(P<0.05).In chest cases,the Dmean of all organs,V12.5 and V13.5 of lung increased with the increase of the grid size.The Dmean of the trachea,esophagus,and aorta in 4mm and 5mm groups,V12.5 and V13.5 of lung and the Dmean of heart in all groups,the Dmean of lung and chest wall in groups which grid size was greater than 2.5mm compared with 1 mm group was statistically significant(P<0.05).In abdomen cases,V15,V21 and Dmean of liver,Dmean of left and right kidney all increased as the grid size increased.V15 of liver in 4mm and 5mm groups,D mean of liver in all groups except the 2.5mm group,and the Dmean of left and right kidney in all groups were statistically significant compared with the 1mm group(P<0.05).3.In the plans of the same site of the case,the larger the grid size,the longer the calculate time was.The difference between each group and the 1mm group was statistically significant(P<0.05).In the plans of different sites of the cases,the calculate time was:abdomen cases>chest cases>head cases.4.In the plans of the same site of the case,the larger the grid size,the more monitor units were.The difference between each group and the 1mm group was statistically significant(P<0.05).In the plans of different sites of the cases,the monitor units were:chest cases>abdomen cases>head cases.5.In the plans of the same site of the case,the larger the grid size,the longer the treatment time was.The difference between each group and the 1mm group was statistically significant(P<0.05).In the plans of different sites of the cases,the treatment time was:chest cases>abdomen cases>head cases.6.In the plans of the same site of the case,the larger the grid size,the lower the gamma pass rate was.The difference between each group and the 1mm group was not statistically significant(P>0.05).In the plans of different sites of the cases,the gamma pass rate was:head cases>abdomen cases>chest cases.Conclusion:Considering the planning quality and planning efficiency,when setting the grid parameter for the volumetric modulated arc stereotactic radiotherapy plan,a grid of no more than 2.5mm is recommended in head cases,a grid of 2mm is recommended in chest cases,and a 2mm or 2.5mm grid is recommended in abdomen cases. |
