Purpose:The leakage and transmission rate(LTR)of the new-type multileaf collimator(MLC)in the Elekta Synergy-S accelerator was measured,the effects of the X-ray energy and gantry angles on the LTR,as well as the application research of LTR in clinic,were discussed.Moreover,the causes of the leakage and transmission dose(LTD)were analyzed.Methods:With a PTW UNIDOS dosimeter and a MP3 3D water tank,under the condition of different Xray energies,the interleaf transmission,between-leaf leakage and leaf ends leakage at the reference position,as well as the LTR with changing the gantry angle,were measured.Moreover,the LTR change curves in the direction of gun-target(GT)and left-to-right(AB)in the isocentric plane were obtained,and the LTR was also measured at 0mm,50mm and 100mm off-axis,respectively.In clinical research,each patient was treated with the whole brain radiotherapy for both Plan 1 and Plan 2,Plan 1 was without jaws,but Plan 2 adopted jaws for shielding leakage and transmission irradiation therein,whose effects on the target volume and organs at risk(OARs,including eyes and lens)were studied.Results:At the reference position,the X-ray energy slightly affected the interleaf transmission,betweenleaf and leaf ends leakages.Moreover,the gravity had slight effect on the between-leaf leakage; the X-ray energy had little effect on the LTD change curves in the GT and AB directions.Based on the same X-ray energy,the LTD was rather low at the point off-axis,which showed a decreased tendency following with the point further away from the axis gradually.Furthermore,different X-ray energies also had a certain effect on the LTD at the same position away from the axis,and the LTRs were larger with 10MV and 18MV of X-ray than that with 6MV.Compared with Plan 1,the dose distribution of the target volume was superior,the maximum doses of eyes and lens were lower for Plan 2.Conclusion:The existence of interleaf leakage radiation remarkably affected the target volume and OARs,the collimator should be rotated using the jaws in accordance with the circumstances when optimizing the radiotherapy plans to protect OARs and normal tissues,which aimed to reduce the risks of irradiation.