扫描视野对乳腺癌调强放射治疗剂量学影响的研究

Dosimetric effects of field of view on intensity-modulated radiotherapy for breast cancer

目的研究不同扫描视野(FOV)CT图像对乳腺癌根治术后放射治疗中危及器官自动勾画及剂量计算精度的影响。方法使用相同扫描条件在患者模拟定位CT等中心处及扩展扫描射野(eFOV)处建立50、60、70和80 cm FOV的电子密度转换曲线并比较其差异;扫描已知体积的标准模体,比较模体在不同FOV重建图像上自动勾画的差异。简单随机抽样选取2020年1月至2022年6月广东省第二人民医院乳腺癌患者30例,获取不同FOV模拟定位CT图像进行危及器官自动勾画,并与医师的勾画进行比较;基于FOV_(50)图像设计治疗计划,将计划移植到不同FOV重建图像进行剂量计算,比较剂量计算结果的差异。结果以不同FOV重建CT图像建立的电子密度转换曲线基本一致。在等中心处,标准模体随FOV增大,模体勾画体积与实际体积差异增大,最大为6 cm^(3)(4.8%);在自动勾画中,脊髓、气管、食管、甲状腺、健侧乳腺和皮肤的勾画精度随FOV增大而减小(t=-28.43~8.23,P<0.05),基于不同FOV图像的剂量计算比较中,锁骨上淋巴结区域靶区V_(95)、最大剂量和平均剂量,危及器官剂量学的差异无统计学意义(P>0.05);计划靶区覆盖度随FOV增大而减小(最大差异为4.06%)。结论乳腺癌根治术后放疗中危及器官自动勾画应选择FOV_(50)重建图像,电子密度转换曲线应依据eFOV区域电子密度模体影像建立,首选eFOV_(80)的重建图像进行剂量计算。

Objective To investigate the effects of CT images reconstructed using different field of view(FOV)sizes on the automatic segmentation of organs at risk and dose calculation accuracy in radiotherapy after radical mastectomy.Methods Under the same scanning conditions,CT values-electron density conversion curves were established by reconstructing the original CT images of a phantom placed at the isocenter and extended FOV(eFOV)positions using FOV sizes of 50,60,70 and 80 cm.Then,these curves were compared.A standard phantom with a known volume was scanned,and the automatic segmentation result of the phantom on CT images reconstructed using different FOV sizes was compared.A total of 30 patients in Guangdong Second Provincial General Hospital from January 2020 to June 2022 with breast cancer were randomly selected.Through simulated positioning,their CT images were reconstructed using different FOV sizes for the purpose of automatic segmentation of organs at risk,followed by comparison between the outcomes of automatic segmentation and physicians′segmentation.The treatment plan established based on CT images reconstructed using a FOV size of 50 cm(FOV_(50) images for short)was applied to CT images reconstructed using FOV sizes of 60,70 and 80 cm(FOV60,FOV70 and FOV_(80) images for short)for dose calculation,and the dose calculation result were compared.Results The CT values-electron density conversion curves derived from CT images reconstructed using different FOV sizes were roughly consistent.At the isocenter,the difference between the segmented volume and actual volume of the standard phantom increased up to a maximum of 6 cm^(3)(4.8%)with an increase in the FOV size.As indicated by the automatic segmentation result,the segmentation accuracy of the spinal cord,trachea,esophagus,thyroid,healthy mammary gland,and skin decreased with an increase in the FOV size(t=-28.43-8.23,P<0.05).The comparison of dose calculated based on CT images reconstructed using different FOV sizes showed that there was no statistically significant differences(P>0.05)in the dose to target volume(V_(95))and the maximum and average doses in the supraclavicular lymph node region,as well as the dose to organs at risk.The coverage for planned target volume decreased with an increase in the FOV size,with a maximum difference of 4.06%.Conclusions It is recommended that,for radiotherapy after radical mastectomy,FOV_(50) images should be selected for the automatic segmentation of organs at risk,CTvalues-electron density conversion curves should be established based on the electron density phantom images of the eFOV region,and the eFOV_(80) images should be preferred for dose calculation.