Objective To compare and analyze DMLC(Sliding Window,SW)and SMLC(Step and Shoot,SS)for delivering IMRT.Methods 5 patients with nasopharyngeal carcinoma were treated with radical intensity modulated radiation therapy using Varian 23EX and Helios tool on a Varian Eclipse system.Different modalities to deliver IMRT were considered for Sliding Window(SW) and Step and Shoot(SS) techniques using a different number of intensity levels(e.g.5,10 and 20).The total beam-on-time,total delivery time and a number of dose-volume parameters regarding PTV and OARs were considered.Results Comparing with the DVH,it was found that SW was the best of the four modalities in the dose distribution of PTV,but SS was better when considering the protection of OARs.The total beam-on-time(MUs) requirement for SS was 9～23% less than SW,but the total delivery time(in minutes)was about twice as long.Conclusion With the number of intensity level of 10 or more,no differences between SS and SW can be appreciated in the dose distribution of PTV and OARs sparing.Referring to the quality assurance,only leaf position needed to be checked in SS,whereas both leaf position and leaf speed need to be checked in SW,so it is proposed to use SS10 for delivering IMRT.

Objective To explore the radiation dose from body γ-knife treatment to the nontargeted region's sensitive organs before and after shielding.Methods 20 patients suffering tumors less than 5 cm were selected.Calibrated thermoluminescence dosimeters (TLD) were placed above the sensitive organs,such as lens,thyroid gland and sexual gland,to measure the radiation dose received before shielding.Different plans were prepared for the patients with lung and renicapsule tumors using calibrators of different size.Radiation dose was measured by the aid of water phantom.For selected lungtumor treatment plan,the radiation doses were measured at the same location on the water phantom shielded with and without 1,2 and 4 cm lead,respectively.Results The maximum doses were 1 023.3 mGy for lens,1 235.7 mGy for thyroid gland and 1 176.8 mGy for sexual glands after treatment,respectively,being higher on the left site than the right.The radiation doses to the sensitive organs were higher for the water phatom with more tartgted points,decreasing by 55％-91％ after being covered with 1,2 and 4 cm lead shieldings.There were significant differences in doses received before and after lead shielding (t =14.4,12.9,13.3,P ＜ 0.05).Conclusions In the course of body γ-knife treatment,the additional factors would increase the dose to the sensitive organs.Therefore,it is necessary to provide lead shielding protection to the teenagers and adults with fertility when they undergo body γ-knife treatment.Trial registration Chinese Clinical Trial Registry,ChiCTR-OOC-16008259.