基于形变配准算法评估前列腺癌分次间剂量的可行性研究

Feasibility of deformable image registration algorithm for interfractional dose calculation in radiotherapy for prostate cancer

目的:研究基于形变配准算法进行前列腺癌分次间剂量评估的可行性。方法:采用锥形束CT(CBCT)形变配准到再计划CT,产生有明显配准误差的形变CBCT。分别结合频谱峰值转换法和逐层线性变换法,根据刚性盆部模体的噪声模型来修正形变CBCT,生成与再计划CT解剖结构基本一致的两组虚拟CBCT作为形变配准评估的“金标准”。以再计划CT为基准,评估计划CT形变配准到虚拟CBCT形成的虚拟CT的Gamma通过率。比较两组虚拟CT的评估系数,验证再计划CT转换为虚拟CBCT的可行性。评估基于形变场映射产生感兴趣区域(ROI)的dice系数,验证基于形变配准中产生形变场的半自动勾画技术的可行性。结果:计划CT形变配准到两组虚拟CBCT产生的虚拟CT的1mm/1%和2mm/2%的Gamma通过率分别为(98.08±0.43)%/(97.95±0.37)%(P>0.05)和(99.53±0.08)%/(99.55±0.10)%(P>0.05)。基于形变场映射产生各个ROI的dice系数均值为0.78~0.95。结论:虚拟CBCT提供了一种解决形变配准算法缺少“金标准”的问题,并验证基于形变配准算法评估前列腺癌分次间剂量的可行性。

Objective To evaluate the feasibility of interfractional dose evaluation based on deformable image registration(DIR)algorithm in the radiotherapy for prostate cancer.Methods A deformed cone beam CT(CBCT)with obvious registration errors was generated by the DIR from cone beam CT(CBCT)to replan CT.Based on the rigid pelvic phantom-based noise model,peak spectrum conversion method and layer-by-layer linear transformation method were used to correct the deformed CBCT and then generate two sets of virtual CBCT in which the anatomical structures were consistent with those in replan CT.The two sets of virtual CBCT were taken as the golden standard of DIR evaluation.The replan CT was taken as the baseline to evaluate the Gamma passing rate of virtual CT generated by the DIR from planned CT to virtual CBCT.The evaluation coefficients of two groups of virtual CT were compared,so as to verify the feasibility of converting replan CT to virtual CBCT.Moreover,the dice coefficient of region of interest generated by deformation field mapping was evaluated,so as to verify the feasibility of semi-automatic segmentation based on the deformation field in DIR.Results The Gamma passing rates(1 mm/1%and 2 mm/2%)of virtual CT derived fromtwo different set of virtual CBCTwere(98.08±0.43)%/(97.95±0.37)%(P>0.05)and(99.53±0.08)%/(99.55±0.10)%(P>0.05).The dice similarity coefficient of region of interest generated based on deformation field was 0.78-0.95.Conclusion Virtual CBCT is a promising method to solve the problem that DIR algorithm lacks of golden standard and to verify the feasibility of DIR-based algorithm to evaluate the interfractional dose in the radiotherapy for prostate cancer.