后装施源器Offset值验证研究

目的 研究后装治疗中多种施源器的Offset值。方法 选取插植钢针(Part#083.062)、插植塑料圆针(Part#189.608)、插植塑料尖针(Part#189.601)、多通道施源器软管(Part#110.800)、塑料宫腔管(Part#189.745)、金属宫腔管(Part#110.437)施源器。根据源在荧光胶片放射性成像,确定施源器顶端驻留点位置以及到施源器顶端的距离。在施源器顶端驻留点位置贴铅珠,将施源器置入盆腔体模中进行CT扫描。然后在计划系统中重建施源器,通过调整Offset值使铅珠与施源器顶端驻留点对准,从而得到施源器Offset值。塑料材质施源器由于密度与人体组织接近,施源器顶端难以准确重建,因此利用挡块或者假源重建施源器,得到塑料材质施源器Offset值。根据验证结果分析比较不同施源器Offset值差异。结果 不同施源器Offset值存在较大差异,其中插植钢针为-11.4 mm,插植塑料圆针为-4.1 mm,插植塑料尖针为-3.5 mm,多通道施源器软管为0 mm或-5.0 mm,塑料宫腔管为-6.5 mm,金属宫腔管为-7.5 mm。结论 为了适应精确放疗的发展趋势,有必要对后装中施源器Offset值进行测量验证。

A verification study of Offset values of different applicators in afterloading brachytherapy

Objective To investigate the Offset values of different applicators in afterloading brachytherapy. Methods Six types of applicators were selected in this study which included stainless steel interstitial needle (Part#083.062),proguide round needle (Part#189.608),proguide sharp needle (Part#189.601),vaginal multi-channel applicator (Part#110.800),fletcher CT/MR applicator (Part#189.745) and henschke titanium applicator (Part#110.437). According to the sources imaging in the fluorography film, the distance of applicators between the first dwell position and the top could be measured. Marker was pasted on the surface of applicator corresponding to the first dwell position. And then the applicator was put into the pelvic phantom for a CT scan. During applicator reconstruction in the treatment planning system, the Offset values of all applicators could be acquired through adjusting the value of offset to superimpose the first dwell and the marker images. On account of the density of plastic material applicators were similar to human tissues, it was difficult to reconstruct the top of the applicator. With the help of stopper or simulation source, the value of offset could be acquired for plastic material applicators. Based on the measurement results, the differences were analyzed among different applicators. Results The Offset values significantly differed among various applicators. The Offset value for stainless steel interstitial needle was -11.4 mm,-4.1 mm for proguide round needle,-3.5 mm for proguide sharp needle, 0 mm or -5.0 mm for vaginal multi-channel applicator,-6.5 mm for fletcher CT/MR applicator and -7.5 mm for henschke titanium applicator, respectively. Conclusion To adapt to the rapid development of precise radiotherapy, it is necessary to verify the Offset value in afterloading brachytherapy.