Abstract
Objective To analyze the impact of dose calculation resolution on Gamma pass rate for planar dose distribution verification of intensity-modulated radiotherapy (IMRT),and to find out the appropriate calculation resolution value with specific applied criteria.Methods 25 IMRT plans were selected for the planar dose verification.The Gamma pass rates with 3 mm/3％,2 mm/2％ and 1 mm/1％ criteria were compared and analyzed.The planar dose distributions were calculatedand exported from TPS with different resolutions of 0.5,1,2,3,4 and 5 mm.The pass rates of Gamma analysis between the computed dose distributions with different resolutions and the dose distributions measured by Mapcheck device were compared and analyzed.Results The average Gamma pass rates of all the 225 fields decreased with the increment of calculation resolution.When the pass rates of Gamma analysis were calculated using 3 mm/3％ criteria,the gamma pass rate with 1 mm and 0.5 mm calculation resolution were (98.3±1.3)％ and (98.3±1.2)％,respectively.The results were almost the same and the difference wasn't statistically significant (P＞0.05).The gamma pass rates with greater than or equal to3 mm calculation resolution were significantly less than the pass rate with 0.5 mm calculation resolution (P＜0.05).When the pass rates of Gamma analysis were calculated using 2 mm/2％ criteria,all the pass rates with greater than 0.5 mm calculation resolution were significantly less than the pass rate with 0.5 mm calculation resolution (P＜0.05).Conclusions The Gamma pass rates of planar dose verification reduce significantly with the increment of calculation resolution.In order to reduce the effect of calculation resolution on Gamma pass rate,the lower calculation resolution should be used.When using the 3 mm/3％ criteria for the Gamma analysis,1 mm calculation resolution is recommended.When using the 2 mn/2％ criteria for the Gamma analysis,0.5 mm calculation resolution is recommended.The appropriate calculation resolution will ensure the reliability of planar dose verification. Key words: IMRT plan verification; Gamma pass rate; Calculation resolution
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