射野影像重建模体内剂量分布的研究  

Reconstruction of dose distribution in phantom from portal image with a backprojection of dosimetric algorithm

作　　者：傅卫华[1] 胡逸民[1] 戴建荣[1] 宋一昕[1] 

机构地区：[1]中国医学科学院中国协和医科大学肿瘤研究所肿瘤医院放疗科,北京100021

出　　处：《中华放射肿瘤学杂志》2006年第4期323-328,共6页Chinese Journal of Radiation Oncology

摘　　要：目的建立一种反向投影算法(模型),由射野影像和患者的CT图像,计算体内的三维剂量分布,进行剂量验证。方法该模型计算体内剂量分布步骤如下：(a)使用电子射野影像系统获取射野影像,将射野影像转换为射出剂量；(b)从射出剂量分布重建入射原射线注量分布；(c)由患者的三维信息(CT图像),计算得到体内的原射线剂量分布；(d)体内散射核叠加,求出体内散射线剂量分布,与原射线剂量相加,即得到体内的剂量分布。使用C语言编程实现算法。通过设置规则、不规则及调强射野,对均匀和不均匀、规则和不规则5种模体进行剂量验证实验,并将计算结果与测量结果进行比较。结果所有实验在射野内、剂量梯度小的区域计算的剂量和测量的剂量的偏差＜5%。在射野边界附近低密度肺组织内的计算剂量和测量的剂量的偏差＞5%。结论所建立的反向投影模型用于剂量验证,其准确性可满足临床要求。但模型还需进一步完善,以准确计算电子失平衡区的剂量。Objective To develop a dosimetric backpmjection algorithm for dosimetric verification. The algorithm would reconstruct a three-dimensional dose distribution in phantom from the treatment beam portal images and the cr images for a patient/phantom. Methods The reconstruction process consisted of four steps： a. To acquire a portal image with an electronic portal imaging device（EPID） and convert it into an exit dose distribution on EPID plane; b. To reconstruct the primary entrance dose distribution from the exit dose distribution; c. To calculate the primary dose distribution in the phantom using the phantom＇s CT image set;and d. To calculate the scatter dose distribution by superposing the scarier kernels in the patient/phantom, then to complete the summation of the primary and the scatter dose distribution to obtain the total dose distribution in the patient/phantom. The dosimetric algorithm was implemented in a C program and apphed to five phantoms： they were homogeneous; inhomogeneous;regular or irregular; irradiated by a regular-shaped; and irregular-shaped or intensity-modulated beam The calculated dose distributions were compared with the measured ones. Retsults For all the experiments, the deviation was 〈 5 % between the calculated and measured dose distribution in the field area with low dose gradients. Large deviation were observed in the field edge with 〉 5 % in the lung, which had a low density. Conclusions The accuracy of the developed backpmjection dosimetric algorithm can meet the clinical requirements of dosimetric verification. This algorithm should be further improved in order to calculate accurately the dose in the region of electronic disequilibrium.

关 键 词：电子射野影像系统 剂量验证 反向投影算法 

分 类 号：R815[医药卫生—放射医学] R730.55[医药卫生—临床医学]