治疗计划系统中CT值及图像质量保证的若干问题讨论

To discuss several question of quality assurance of CT value and image using by treatment planning system

目的:了解CT扫描时影响CT值的相关条件;讨论不同扫描参数扫描得到的CT重建图像可能产生的误差;对三维治疗计划系统使用的CT值及图像的质量保证的若干问题进行探讨。材料和方法:对SiemensSomatomPlus4螺旋CT设置不同扫描电压和电流,测量Gammex的RMI467体模中不同材料的密度值与CT值关系。测量CT孔径位置以及高密度材料治疗床板可能对CT值产生的影响。测量包含不同浓度造影剂的水溶液的CT值及相应的等效密度,初步对鼻咽癌病人加入造影剂前后的CT图像相对剂量计算的影响进行了估计。扫描一包含空腔的有机玻璃板,改变扫描层厚和螺距,对比ADAC三维治疗计划系统重建的CT图像与真实形态的差别。此外对使用的数字化仪以及打印设备进行了图像输入和输出的检查,检查了系统的文字和图像信息的登记和输出。结果:给出了不同电压和电流下CT值与密度的关系;对造影剂、CT治疗床等相关因素对CT值的影响给出了定量讨论;对有机玻璃模体的扫描结果表明:由于部分容积效应和阶梯状伪影的影响,CT图像中显示的空腔形态发生了改变。其他对治疗计划系统非剂量学质量保证措施也在计划系统使用前进行了检查。结论:对于三维治疗计划系统,正确输入密度-CT值是保证剂量计算正确的条件之一;

Purpose: To know the relative influence with CT value in CT scan; discussing the error of the CT reconstruct image with different scan parameters; to discuss the several question of quality assurance of CT value and image using by three dimension treatment planning system. Materials and Methods: Set different scan voltage and current to Siemens Somatom Plus4 helical CT- measured the different material density relative to CT value with the Gammex 467 phatom-.Measured the effect of the CT value when the phatom in different position of CT and the high density material of CT bed.Measured the CT value relative the density of the water including the different density contrast dose. Estimated the referent dose influence of the patient of Nasopharyngeal carcinoma who added the contrast dose.Scan a phatom including a air cavity- change the scanning slice thickness and pitch- checked the difference of the reconstruct CT image with the real size. Checked the image inputting and outputting of the using digital board and printers. Checked the registering and output of the information of the words and images of the system. Results: Give the relative curve of the CT value with the different scan voltage and current; Gived the result of CT bed and contrast dose influencing the CT value; the scan result of the phatom indicated that the shape of the air cavity in the CT image change because of part volume effect and ladder artifact. Other none-dose quality assurance had performed before using the treatment planning system. Conclusion: Inputting the correct density-CT value is one condition of right dose calculation; to know the error of CT image can reduce the error when drawing the outline of target.The three dimension treatment planning system before using need detail quality assurance.