多叶准直器在肿瘤适形放疗中的应用

Application of Multi-leaf Collimator in Tumor Conformal Radiotherapy

目的临床应用多叶准直器(MLC)放疗时要对MLC进行验收、校对和剂量测量。材料和方法对MLC的位置精度进行检测,测量MLC的透射率和漏射率,用慢感光胶片分别测量MLC和低熔点铅的半影(20%～80%)。选15例经医生确认的放疗计划,比较低熔点铅和MLC适形所做计划放疗体积的变化。结果在(20×20)cm2野内,叶片的误差在0～±1.3mm,6MVX线MLC的透射率为2.2%～2.9%,略低于低熔点铅在厚度为8cm的透射率3.3%。相对叶片的间隙为0～6mm时漏射率为0%～53.7%。MLC的半影大于低熔点铅挡块的半影0.36～1.37mm,边界放大(Margin50%～90%)的大小MLC平均为3.52mm,低熔点铅平均为2.78mm。综合各种其他误差我们制定治疗计划时头颈部肿瘤Margin一般放大5～8mm。对体部肿瘤Margin一般放大7～10mm。结论多叶准直器的适形程度和肿瘤的大小没有直接关系,而仅仅和射束方向观察(BEV方向)的照射野的形状和叶片的宽度有关。当采用更窄的叶片并且肿瘤在BEV方向照射野的形状更加规则时,就能达到更好的适形。

Objective When applying multi-leaf collimation （MLC） to do radiotherapy.we should check, collate and do dose measurement to MLC. Material and Methods Checked the accuracy of the leaf position in the light field, and measured the transmittance and leakage rate of MLC.Measured the low melting point lead penumhrao using slow light-sensitive film.Chose 15 cases to compare their radiotherapy volume change of low melting point lead and eonformal radiotherapy. Results The change of leaf position was 0-± 1.3mm,the rate of transmission of the MLC was 2.2%-2.9%,which was 3.3% less than low melting point alloy （high 8cm）. When the gap of the leaves face to face was 0-6mm,the rate of leakage. of the MLC was 00-53.7%. The penumbra of the MLC was 0.36-1.37mm larger than the block.The average of margin（50%-90%） of MLC was 3.52mm,the block was 2.78.The margin of target of the head-neck was 5-8mm.Conclusion The canformal degree of MLC was depended on the shapes of target in beams eye view and the wide of the leaf.When adnpting narrower leaf and the shape of tumor in BEV direction were more regular,the conformal degree of MLC would be better.