不同CT赋值方法对脑转移放疗剂量计算的影响研究

Q4 Medicine
Jianxin Ren, G. Gong, Xingmin Ma, X. Yao, Yong Yin
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Three groups of pseudo CT were generated by three CT values assignment methods based on the CT images: whole tissue was assigned 140 HU; cavity, bone and other tissues were assigned -700 HU, 700 HU and 20 HU, respectively; different tissues and organs were assigned corresponding CT values. The dose distribution of Plan1 was recalculated on three groups of pseudo-CT to obtain Plan2, Plan3 and Plan4, respectively. Finally, the dosimetric difference between Plan1 and other plans (including Plan2, Plan3 and Plan4) were compared. \n \n \nResults \nThe average CT values of bone and cavity were (735.3±68.0) HU and (-723.9±27.0) HU, respectively. The average CT values of soft tissues was mostly distributed from -70 to 70 HU. The dosimetric differences between Plan2, Plan3, Plan4, and Plan1 decreased in turn. The differences of maximum dose of lens were the biggest, which can reach more than 5.0%, 1.5%-2.0% and 1.0%-1.5%, respectively, and the differences of other dose parameters were basically less than 2.0%, 1.2% and 0.8%, respectively. In the pixelwise dosimetric comparison, the areas with more than 1% difference in the local target cases were mainly distributed in the skin near the field. On the other hand, those in the whole brain target cases were mainly distributed at the bone, cavity, bone and soft tissues junction, and the skin near the field. In addition, the dose calculation error of CT value assignment methods in 3D-CRT plan was slightly larger than that in IMRT plan, and that in whole brain target cases were significantly larger than that in local target cases. \n \n \nConclusions \nDifferent CT value assignment methods have a significant effect on the dose calculation of radiotherapy for brain metastases. 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引用次数: 0

摘要

目的探讨不同CT赋值方法对脑转移瘤放疗方案剂量计算的影响,为基于MR影像的放疗方案提供参考。方法选择35例接受放射治疗的脑转移患者,当日行术前CT和MR模拟定位。根据模拟CT图像,计算三维适形放射治疗(3D-CRT)或调强放射治疗(IMRT)方案为原方案(Plan1)。对CT和MR图像进行严格配准,然后在CT和MR图像上圈定主要组织器官。计算各组织器官的平均CT值。基于CT图像,采用三种CT值赋值方法生成三组伪CT:全组织赋值140 HU;腔、骨和其他组织分别赋值为-700 HU、700 HU和20 HU;不同的组织器官被赋予相应的CT值。在三组伪ct上重新计算Plan1的剂量分布,分别得到Plan2、Plan3和Plan4。最后比较计划1与其他计划(包括计划2、计划3和计划4)的剂量学差异。结果骨、腔平均CT值分别为(735.3±68.0)HU和(-723.9±27.0)HU。软组织CT平均值多分布在-70 ~ 70 HU。计划2、计划3、计划4和计划1之间的剂量学差异依次减小。晶状体最大剂量差异最大,分别可达5.0%、1.5% ~ 2.0%和1.0% ~ 1.5%以上,其他剂量参数差异基本分别小于2.0%、1.2%和0.8%。在像素级剂量学比较中,局部靶病例差异大于1%的区域主要分布在近场皮肤。而全脑靶病例主要分布在骨、腔、骨与软组织交界处及近场皮肤。此外,3D-CRT计划CT赋值方法的剂量计算误差略大于IMRT计划,全脑靶病例的剂量计算误差明显大于局部靶病例。结论不同CT赋值方法对脑转移瘤放疗剂量计算有显著影响。当分别对骨、腔、软组织给予适当的CT值时,剂量计算偏差基本控制在1.2%以内。通过对各组织器官分配肿块CT值,偏差进一步控制在0.8%以内,可以满足临床要求。关键词:脑转移瘤;CT值;伪CT;剂量的比较
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Study on the effects of different CT values assignment methods on dose calculation of brain metastases radiotherapy
Objective To study the effects of different CT values assignment methods on the dose calculation of radiotherapy plan for brain metastases, which will provide a reference for radiotherapy treatment planning based on MR images. Methods A total of 35 patients treated with radiotherapy for brain metastases were selected, with pre-treatment CT and MR simulated positioning performed at the same day. Based on the simulation CT images, three dimensional conformal radiation therapy (3D-CRT) or intensity modulated radiation therapy (IMRT) plans were calculated as the original plan (Plan1). The CT and MR images were rigidly registered and then the main tissues and organs were delineated on CT and MR images. The average CT values of each tissue and organ were calculated. Three groups of pseudo CT were generated by three CT values assignment methods based on the CT images: whole tissue was assigned 140 HU; cavity, bone and other tissues were assigned -700 HU, 700 HU and 20 HU, respectively; different tissues and organs were assigned corresponding CT values. The dose distribution of Plan1 was recalculated on three groups of pseudo-CT to obtain Plan2, Plan3 and Plan4, respectively. Finally, the dosimetric difference between Plan1 and other plans (including Plan2, Plan3 and Plan4) were compared. Results The average CT values of bone and cavity were (735.3±68.0) HU and (-723.9±27.0) HU, respectively. The average CT values of soft tissues was mostly distributed from -70 to 70 HU. The dosimetric differences between Plan2, Plan3, Plan4, and Plan1 decreased in turn. The differences of maximum dose of lens were the biggest, which can reach more than 5.0%, 1.5%-2.0% and 1.0%-1.5%, respectively, and the differences of other dose parameters were basically less than 2.0%, 1.2% and 0.8%, respectively. In the pixelwise dosimetric comparison, the areas with more than 1% difference in the local target cases were mainly distributed in the skin near the field. On the other hand, those in the whole brain target cases were mainly distributed at the bone, cavity, bone and soft tissues junction, and the skin near the field. In addition, the dose calculation error of CT value assignment methods in 3D-CRT plan was slightly larger than that in IMRT plan, and that in whole brain target cases were significantly larger than that in local target cases. Conclusions Different CT value assignment methods have a significant effect on the dose calculation of radiotherapy for brain metastases. When appropriate CT values are given to bone, air cavity and soft tissue, respectively, the deviation of dose calculation can be basically controlled within 1.2%. And by assigning mass CT values to various tissues and organs, the deviation can be further controlled within 0.8%, which can meet the clinical requirements. Key words: Brain metastases; CT values; Pseudo CT; Dose comparison
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中华放射医学与防护杂志
中华放射医学与防护杂志 Medicine-Radiology, Nuclear Medicine and Imaging
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