呼吸门控PET/CT对于肺癌放疗靶区勾画的指导

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。

Guiding the target delineation in radiation therapy of lung cancer by respiratory gated PET/CT

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.