Effect of dMLC dosimetric leaf gap in IMRT and VMAT / 中华放射医学与防护杂志

ABSTRACT

Objective To explore the relationship between DLG value and planning dose distribution and actual treatment dose distribution.Methods IMRT and VMAT plans were generated in Eclipse TPS for a typical whole pelvis case,separately.For IMRT plan,MLC position and actual fluence were calculated for each DLG value with the same optimal fluence.Plans with different DLGs of 0 cm and 0.3 cm were compared by several dosimetric indexes.For exploring the PTV mean dose difference between planning dose and actual IMRT or VMAT treatment,planning dose was recalculated with fixed MLC position and different DLGs.Results Dosimetric differences of PTV V50,rectum V40,bladder V40,small bowel V35,left and right femoral head Dmax were 1.49％,0.72％,0.82％,0.68％,0.02 and 0.14 Gy respectively,the average leaf pair width of MLC segments was correlated with DLG (R2 =0.996,P ＜0.05) and reduced with the increase of DLG.In actual treatment,3.95％ and 1.5％ mean dose reduction in PTV were observed while DLG increased per 0.1 cm in the typical pelvis case,in IMRT and VMAT treatment respectively.Conclusions DLG can result in the change of MLC position and the dose difference between planning and actual treatment.