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肿瘤体积的大小直接影响放疗靶区的划定,但由于肺部呼吸运动引起靶组织位移的原因,常常影响瘤体体积的判定。早期文献报道采用呼吸门控PET/CT有助于肺部占位体积的精确计算[1-2],近年来文献大多报道了四维PET与三维PET相比肿瘤位置的变化,也有关于体积变化的研究[3]。此外,四维CT通过对一个呼吸周期内不同呼吸时期肿瘤体积的连续捕捉,有效减轻了呼吸运动产生的伪影,从而得到了广泛应用。许多学者比较了四维CT体积与三维CT体积的差别[4-6],以获得对肿瘤靶区的准确勾画。
本研究通过对肺部肿瘤进行呼吸门控PET/CT采集与常规采集,比较肺部不同位置结节的四维PET体积与三维PET体积的差别,以及四维CT体积与三维CT体积的差别,给予肺部肿瘤放疗靶区勾画指导,最终使患者接受合理的照射剂量。
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本研究共20个恶性肺结节(表 1),其中5个位于上肺,2个贴近胸膜,6个位于肺门,7个位于下肺。运动幅度为1.0~6.4 mm,平均3.3 mm。对每个结节进行常规PET/CT采集,得到三维PET体积,后进行呼吸门控PET/CT采集,分别用40%阈值法和MIP法两种方法测量得到平均四维PET体积。所有结节的三维PET体积为9.5 cm3,40%阈值法得到的平均四维PET体积为9.7 cm3,比三维PET体积大14.4%;MIP法得到的平均四维PET体积为11.0 cm3,比三维PET体积大20%。
结节序号 位置 运动幅度(mm) 三维PET体积(cm3) 平均四维PET体积(cm3) 40%阈值法 最大密度投影法 1 上肺 4.1 7.0 7.4 8.1 2 上肺 1.0 2.0 2.1 2.2 3 上肺 1.5 0.2 0.6 0.4 4 上肺 1.5 10.1 10.1 9.8 5 下肺 1.7 3.6 4.2 3.6 6 下肺 5.1 3.0 2.0 2.8 7 胸膜 1.0 45.5 42.1 45.0 8 肺门 3.8 2.1 2.2 2.3 9 下肺 3.0 32.9 33.5 36.8 10 上肺 2.0 4.5 4.7 4.6 11 肺门 2.5 7.9 7.7 6.9 12 下肺 7.1 7.0 8.2 12.3 13 下肺 3.3 3.8 4.1 4.2 14 胸膜 1.3 9.6 9.0 10.4 15 下肺 6.4 10.0 11.9 16.5 16 肺门 2.0 14.9 15.5 16.8 17 肺门 4.6 1.6 2.4 3.2 18 肺门 3.1 3.4 4.7 6.9 19 下肺 4.6 14.0 14.3 14.9 20 肺门 5.6 6.2 7.0 7.2 表 1 20个结节的三维PET体积与平均四维PET体积比较
Table 1. Comparison of gross tumor volume of twenty nodules defined by average four-dimensional PET and three-dimensional PET
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图 1为两种方法测得的平均四维PET体积与三维PET体积的比较结果,其中只有4个结节的三维PET体积小于平均四维PET体积,其余16个结节的平均四维PET体积大于三维PET体积,平均四维PET体积比三维PET体积大17.2%。图 2为平均四维PET体积与三维PET体积的相对差值与结节呼吸运动幅度及结节位置的关系,由图可见,除2个结节外,下肺和肺门的平均四维PET体积均大于三维PET体积,平均相对差值为26.5%;除1个结节差值较大外(155%),上肺和胸膜平均四维PET体积与三维PET体积的平均相对差值为2.7%。当结节呼吸运动幅度小于3 mm时,平均四维PET体积与三维PET体积的平均相对差值为1.8%;大于3 mm时,平均相对差值为24.3%。
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图 3为20个结节的三维CT体积与平均四维CT体积的比较结果,结节的基本信息与表 1一致。CT肺窗体积均远远大于PET体积。其中,13个结节6个时相的平均四维CT体积大于三维CT体积。三维CT体积为14.7 cm3,平均四维CT体积为15.2 cm3,平均四维CT体积比三维CT体积大3.9%。
图 3 20个结节的平均四维CT体积与三维CT体积的相对差值
Figure 3. Relative difference of gross tumor volume of twenty nodules defined by average four-dimensional CT and three-dimensional CT
图 4为三维CT体积与平均四维CT体积的相对差值与结节呼吸运动幅度及结节位置的关系。由图可见,对于下肺,除1例结节外,平均四维CT体积明显大于三维CT体积,平均相对差值为11.3%;对于上肺、肺门、胸膜,平均四维CT体积与三维CT体积比较没有规律。结节呼吸幅度与体积相对差值亦无明显规律,对于呼吸幅度大于3 mm的结节,平均四维CT体积与三维CT体积的平均相对差值为11.8%;对于呼吸幅度小于3 mm的结节,平均相对差值为7.4%。
图 4 20个结节的平均四维CT体积与三维CT体积的相对差值随结节呼吸运动幅度的变化
Figure 4. The changes of relative difference with respiratory motion amplitude of gross tumor volume of twenty nodules defined by aver- age four-dimensional CT and three-dimensional CT
本研究请一位放疗科医师在下肺某结节勾画常规靶区与呼吸门控靶区,并显示其差别(图 5)。由图可见,平均四维PET体积大于三维PET体积,而平均四维CT体积远远大于平均四维PET体积,因此,采用符合恶性肿瘤的生物学特点的平均四维PET体积勾画靶区,缩小了靶区。同时,平均四维CT体积大于三维CT体积,但并不能完全将其包含于内,然而考虑到四维CT体积涵盖呼吸信息,所以对上肺和胸膜的结节采用低剂量平均四维CT体积勾画靶区。
呼吸门控PET/CT对于肺癌放疗靶区勾画的指导
Guiding the target delineation in radiation therapy of lung cancer by respiratory gated PET/CT
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摘要:
目的 目的通过对肺部肿瘤进行呼吸门控PET/CT研究,给予肺部肿瘤放疗靶区勾画指导,最终使患者接受合理的照射靶区。 方法 对20个恶性结节进行呼吸门控PET/CT与常规PET/CT采集,比较肺部不同位置结节的平均四维PET体积与三维PET体积的差别,以及平均四维CT体积与三维CT体积的差别。以平均四维体积与三维体积的相对差值作为体积间的差异, 分别从结节位置、运动幅度研究其对四维体积与三维体积的影响。 结果 用两种方法测得的平均四维PET体积比三维PET体积大17.2%。体积相对差值与结节呼吸运动幅度及结节位置有关。下肺和肺门病灶平均四维PET体积与三维PET体积的平均差值为26.5%,远远大于上肺和胸膜病灶的平均差值(2.7%)。当结节呼吸运动幅度大于3 mm时,四维与三维PET体积差值的平均值为24.3%;小于3 mm时,平均值为1.8%。平均四维CT体积比三维CT体积大3.9%,体积差值范围为0.2~5.9 cm3,体积比值为1.10依0.32。只有在下肺,平均四维CT体积明显大于三维CT体积,平均差值为11.3%。 结论 对于靠近肝脾的下肺结节,用平均四维PET勾画肿瘤靶区更精确些;对于肺门周围的结节,考虑平均四维PET体积作为肿瘤靶区;对于上肺和胸膜的结节,建议采用低剂量呼吸门控扫描且已经考虑了呼吸运动的平均四维CT体积勾画靶区。 -
关键词:
- 肺肿瘤 /
- 正电子发射断层显像术 /
- 体层摄影术,X线计算机 /
- 放疗靶区 /
- 体积比较
Abstract:Objective To give target outline guidance for lung tumor radiation therapy by respiratory gating(RG) four-dimensional PET/CT for lung cancer. Eventually reasonable radiation target regions in treatment planning are received by patients. Methods Twenty malignant nodules were studied by RG PET/CT and conventional PET/CT. The differences of gross tumor volume defined by average four-dimensional PET and three-dimensional PET were compared in different lung locations. Differences of gross tumor volume defined by average four-dimensional CT and three-dimensional CT were also investigated. Differences between volume defined by average four-dimensional volumes and three-dimensional volumes were defined as relative difference of gross tumor volume, and influences for volume defined by four-dimensional PET and CT and three-dimensional PET and CT based on the nodal position and respiratory motion amplitude were also investigated in this study. Results Both volumes defined by average four-dimensional PET measured with two techniques were 17.2% greater than the volume defined by three-dimensional PET on average. The relative difference of the volume defined by average four-dimensional PET and three-dimensional PET was related to the nodal position and respiratory motion amplitude. The mean difference was 26.5% for the lower lobe and hilus of the lung, which was much greater than that of the upper lobe and pleura(2.7%). When the respiratory motion amplitude of nodules was > 3 mm, the difference between the volumes defined by average four-dimensional PET and three-dimensional PET was 24.3%(as < 3 mm, difference was 1.8%). The volume defined by average four-dimensional CT was 3.9% larger than the volume defined by three-dimensional CT, with difference range of nodule volume at 0.2 cm3 to 5.9 cm3 and ratios of 1.10±0.32. Only the nodules in the lower lobe showed significantly larger volumes defined by average four-dimensional CT than those defined by three-dimensional CT with average difference of 11.3%. Conclusion For lung nodules close to the liver and spleen, the volume defined by average four-dimensional PET showed more accuracy for sketching tumor target. For nodules around the hilus of the lung, the volume defined by average four-dimensional PET can be considered as tumor target. For the upper lobe and pleural nodules, the volume defined by average four-dimensional CT was selected for the target outline, which adopted low-dose RG scan and considered breathing movement. -
表 1 20个结节的三维PET体积与平均四维PET体积比较
Table 1. Comparison of gross tumor volume of twenty nodules defined by average four-dimensional PET and three-dimensional PET
结节序号 位置 运动幅度(mm) 三维PET体积(cm3) 平均四维PET体积(cm3) 40%阈值法 最大密度投影法 1 上肺 4.1 7.0 7.4 8.1 2 上肺 1.0 2.0 2.1 2.2 3 上肺 1.5 0.2 0.6 0.4 4 上肺 1.5 10.1 10.1 9.8 5 下肺 1.7 3.6 4.2 3.6 6 下肺 5.1 3.0 2.0 2.8 7 胸膜 1.0 45.5 42.1 45.0 8 肺门 3.8 2.1 2.2 2.3 9 下肺 3.0 32.9 33.5 36.8 10 上肺 2.0 4.5 4.7 4.6 11 肺门 2.5 7.9 7.7 6.9 12 下肺 7.1 7.0 8.2 12.3 13 下肺 3.3 3.8 4.1 4.2 14 胸膜 1.3 9.6 9.0 10.4 15 下肺 6.4 10.0 11.9 16.5 16 肺门 2.0 14.9 15.5 16.8 17 肺门 4.6 1.6 2.4 3.2 18 肺门 3.1 3.4 4.7 6.9 19 下肺 4.6 14.0 14.3 14.9 20 肺门 5.6 6.2 7.0 7.2 -
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