基于锥形束CT的直肠癌患者放疗中实际吸收剂量探讨

Actual absorbed dose in radiotherapy of patients with rectal cancer based on cone-beam CT

直肠癌放射治疗中,由于摆位误差的存在,患者体内实际得到的剂量与计划设计相比总有不同程度的差异。选取20例直肠癌RapidArc病例,首先将pCT图像的治疗计划移植到散射校准后的锥形束CT(CBCT)图像上生成初始CBCT计划,随后该计划经每周的摆位误差数据修正等中心位置后进行剂量计算,生成修正后的CBCT计划,最后用配对t检验比较CBCT计划与pCT计划剂量计算结果的差异。结果显示:CBCT计划的剂量学参数结果与pCT计划相比,靶区D2、D98、D50、CI、HI的平均值均在一定程度上减小,差异依次为2.8%、2.5%、2.9%、2.0%、4.4%,均有统计学意义(p<0.001);在小肠中Dmean、D5、V20、V30和V40的平均值均有一定程度的增大,差异依次为3.0%、3.1%、2.5%、3.1%、3.6%,均有统计学意义(p<0.001);在膀胱中Dmean、D5、V20、V30和V40的平均值均在一定程度上增大,差异依次为3.0%、1.8%、0.9%、3.2%、3.4%,均有统计学意义(p<0.001);左右股骨头的差异较小(最大为0.3%,最小为0.1%),但结果均有统计学意义(p<0.001)。实验结果提示:基于散射校准后的CBCT图像结合摆位误差数据制定的CBCT计划,可为直肠癌患者放疗中各组织实际吸收剂量提供参考,为临床使用中定量评估治疗效果提供数据支持。

In the radiotherapy of rectal cancer,the actual dose received by the patient's body always differs from the planned design due to setup errors.Twenty rectal cancer cases undergoing RapidArc treatment were selected.The treatment plan of the pCT images was transplanted to the scatter-corrected cone-beam computed tomography(CBCT)images.Then,the dose was calculated to generate the revised CBCT plan after the raw CBCT plan was corrected using the weekly setup error data.Finally,a paired t-test was used to compare the results of the dose calculation between the CBCT and pCT plans.This showed that the dosimetric parameter average values of D2,D98,D50,CI,and HI in the target of the CBCT plan were lower than those in the pCT plan.The differences of 2.8%,2.5%,2.9%,2.0%,and 4.4%,respectively,were statistically significant(p<0.001).The dosimetric parameter average values of Dmean,D5,V20,V30,and V40 in the small intestine of the CBCT plan were higher than those in the pCT plan.The differences of 3.0%,3.1%,2.5%,3.1%,and 3.6%,respectively,were statistically significant(p<0.001).The dosimetric parameter average values of Dmean,D5,V20,V30,and V40 in the bladder of the CBCT plan were higher than those in the pCT plan.The differences of 3.0%,1.8%,0.9%,3.2%,and 3.4%,respectively,were statistically significant(p<0.001).The difference between the left and right femoral heads was small(maximum difference:0.3%,minimum difference:0.1%);however,statistical significance was found(p<0.001).The comparative analysis indicates that the CBCT plan,based on scatter-corrected CBCT images combined with setup error data,provides a reference for the actual absorbed dose of each tissue in rectal cancer radiotherapy.These findings are useful for the quantitative evaluation of the therapeutic effect of radiotherapy for rectal cancer.