头颈肩定位体架对放射治疗剂量的影响

Effect of head, neck and shoulder body-frame on radiotherapy dosage

目的:测量分析Civco、滕飞宇、华宇新3种头颈肩固定体架的穿射率、Gamma通过率等,探讨体架对放疗剂量的影响,为今后的临床工作提供参考数据。方法:扫描体架的CT图像并读取体架CT值,使用指形电离室测量不同开野条件的体架穿射率,分析体架材料与散射对射线能量衰减的影响;制订固定机架角Gan=0°和两组容积弧形调强放射治疗(VMAT)计划,通过电子射野影响系统获取治疗床上是否放置体架的图像,应用PD(Portal Dosimetry)软件模块分析profile曲线与Gamma通过率,分析体架对剂量验证的影响。结果:体架对射线能量的衰减低于2%,不同开野条件下散射对穿射率的影响在0.1%~1%内。治疗床上放置Civco、滕飞宇、华宇新体架与只有治疗床的PD图像的Gamma(2%、2 mm)通过率分析,机架角0°时分别为100.0%、93.4%、63.9%,VMAT照射时分别为99.7%、27.6%、19.6%。结论:头颈肩定位体架对剂量有衰减,且3种体架的穿射率、Gamma通过率等有所差别,在制订放疗计划时应该充分考虑头颈肩定位体架的影响以提高靶区剂量的精确性。

Objective To study the effect of body-frame on radiotherapy dosage and provide reference data for clinical work in future by measuring and analyzing the X ray transmission rate and Gamma passing rate of 3 kinds of head, neck and shoulder body-frame（Civco, Teng Feiyu, Hua Yuxin body-frame）. Methods After the body-frame was scanned to obtain the body-frame CT image and the CT value was read out, the X ray transmission rates of body-frame at various open-fields of different sizes were measured with a thumb ionization chamber in order to analyze the X-ray energy attenuation caused by the material and scattering of body-frame. When the gantry angle was fixed at 0°, or volumetric modulated arc therapy（VMAT） was used, the image with or without body-frame on the treatment couch was obtained with EPID. Finally, the profile curve and Gamma passing rate were analyzed with Portal Dosimetry（PD） software for evaluating the effect of body-frame on dose verification. Results The X-ray went through the body-frame, resulting in energy attenuation which was less than 2%. X-ray energy attenuation caused by the scattering of body-frame was within 0.1%-1.0%.When the Gantry angle was fixed at 0°, Gamma passing rates of the comparison between the PD image with frame on the treatment couch and no frame were 100%（Civco）, 93.4%（Teng Feiyu）, and 63.9%（Hua Yuxin）. The Gamma passing rates（2%/2 mm） for VMAT plans were 99.7%（Civco）, 27.6%（Teng Feiyu）, 19.6%（Hua Yuxin）.Conclusion All the 3 kinds of head, neck and shoulder body-frame lead to dose attenuation, and some differences exists in transmission rate and Gamma passing rate among them. When we make the radiotherapy plans, the impact of body-frame on radiotherapy dosage should be considered in order to ensure that the prescription is delivered accurately.