空气间隙、射线过滤模式、计算模型和光束倾角在不同补偿膜厚度条件下对皮肤剂量的影响

Effects of Air Gap,Radiation Filtering Mode,Calculation Model and Beam Inclination Angle on Skin Dose Under Different Compensation Film Thickness

目的基于联影uRT-TPS建模,探讨空气间隙、射线过滤模式、计算模型和光束倾角在不同补偿膜厚度条件下对皮肤剂量的影响。方法利用固体水层板,通过改变空气间隙大小(0、2、4和6 mm)、补偿膜厚度(0、5、10、15和20 mm)分别构建17种模体模型,在uRT-TPS中通过改变射线过滤模式、计算模型(MC和Convolution)和光束倾角(0°~80°)这3类变量对这17种模体模型设计248个治疗计划,在满足所有计划靶区层平均剂量达到1000cGy的条件下,获得皮肤层平均剂量(Da或Dt)和皮肤层剂量增强因子(div)。结果补偿膜厚度在0~10 mm范围内,Dt随厚度增加而增加。补偿膜为5 mm时,4 mm空间间隙的Dt最大,0 mm空间间隙的div最小。无补偿膜时,FFF模式下的Da值高于FF模式,且FF和MC条件下的Da值偏高。有补偿膜时,FF和MC条件下的div偏低。div随光束倾角增大而增大,且FF模式下的div值随补偿膜的增加而降低,而FFF模式下的div值随补偿膜的增加而增加。结论在表浅肿瘤放射治疗中,皮肤剂量受到补偿膜厚度、空间间隙、射线过滤模式、计算模型和光束倾角5类因素的综合影响,临床实践应结合需求灵活调整,尽可能降低皮肤剂量。

Objective To explore the effects of air gap,radiation filtering mode,calculation model and beam inclination on skin dose under different compensation film thickness based on the combined imaging uRT-TPS model.Methods 17 phantom models were constructed by changing the size of air gap(0,2,4 and 6 mm)and the thickness of compensation film(0,5,10,15 and 20 mm)using a solid water layer plate.In uRT-TPS,248 treatment plans were designed for these 17 phantom models by changing three types of variables:ray filtering mode(FF and FFF),calculation model(MC and Convolution)and beam inclination(0°-80°),under the condition that the average dose of all planned target areas reached 1000 cGy,the average dose of skin layer(Da or Dt)and the dose enhancement factor of skin layer(div)were obtained.Results The thickness of compensation film was within 0-10 mm,and Dt increases with the increase of thickness.When the compensation film was 5 mm,the Dt of 4 mm space gap was the largest,and the div of 0 mm space gap was the smallest.Without compensation film,the value of Da under FFF mode was higher than that under FF mode,and the value of Da under FF and MC conditions was higher.With compensation film,div under FF and MC conditions was low.Div increases with the increase of beam inclination,and div value in FF mode decreases with the increase of compensation film,while div value in FFF mode increases with the increase of compensation film.Conclusion In the radiotherapy of superficial tumors,the skin dose is affected by five factors:compensation film thickness,space gap,radiation filtering mode,calculation model and beam angle.Clinical practice should be flexible to adjust according to the needs,and reduce the skin dose as much as possible.