基于Eclipse研究不同人体替代组织的深度剂量特性

The depth dose characters of different tissue substitutes based on Eclipse

目的研究放射治疗计划中不同人体组织深度剂量沉积特点。方法在Eclipse计划系统中建立20 cm×20cm×20 cm水模体,然后在水模体中心轴处,深度3cm下建立含不同人体替代组织的模体结构,并赋予组织密度值和CT值,射野10 cm×10 cm,使用6 MV X射线SSD=100 cm照射,提取射野中心轴深度剂量曲线数据与水模体中深度剂量曲线比较。结果当给予6MV X射线照射时,含空气和肺组织模体均在组织和水材料下交界后出现二次剂量建成,且剂量值下降大大慢于单纯水模体;含骨骼肌和脂肪组织模体中的深度剂量线和单纯水模体相比相差较小,其中含骨骼肌模体中深度剂量线基本与水模体中相同,而含脂肪模体中数值略高于水模体的;含骨组织、铝模体和水材料的上交界后出现二次剂量建成现象,而和水材料下交界后剂量快速下降;含各种组织的模体在达到一定深度后剂量曲线均趋于平行。结论当射线由低密度物质进入高密度物质后会产生二次剂量建成效应,且密度差异越大建成效应越明显;当射线由高密度物质进入低密度物质后,深度吸收剂量快速降低,且密度差越大降低速度越快。这种深度剂量特性对制定放射治疗计划可起到一定的指导作用。

Objective Researching the characters of depth dose deposition of different tissue substitutes. Methods The water phantom( 20 cm × 20 cm × 20 cm) is built in Eclipse TPS,then different tissue substitutes models which assigned density and CT values are set up 3 cm under the water phantom surface at the center axis. A radiation field,6 MV X-ray,10 cm ×10 cm,SSD = 100 cm,is given to different models,then we extract the center axis depth dose which are used to compared with the one in pure water phantom. Results The dose curves in water phantom with air and lung appear second dose built-up effect below the inferior interface,and the rate of descend of the dose value is significantly slower then the one in pure water phantom. The depth dose values in the phantom included Muscle-Skeletal and Adipose-Tissue are mainly as same as the ones in pure water phantom,but the dose curve in Adipose-Tissue is slightly on top of the curve in pure water phantom;The depth of dose curves in Bone and AL model below the superior interface appear the second dose built-up effect,but the rate of descend of the dose value in them decreases rapidly below the inferior interface. All the curves tend to be parallel to the one in pure water phantom after a certain depth. Conclusion The second dose built-up effect will appear when X-ray passes through from low density substance to high density substance,and the greater of the density difference,the more obvious of the effect.The depth dose decreases rapidly when the X-ray passes through from high density substance to low density substance,and the greater density difference will lead to more obvious phenomenon. The depth dose characters can be useful in TPS planning design.