Cavedon C, Giri M G, Zivelonghi E, Grigolato D, Zuffante M, Ferdeghini M
Azienda Ospedaliera Universitaria Integrata - Verona - Italy.
Med Phys. 2012 Jun;39(6Part8):3691. doi: 10.1118/1.4735007.
To find an optimized workflow for the use of respiratory-gated PET (4D-PET) in target volume delineation of tumors subject to respiratory-gated radiation therapy.
15 patients with lung (11) and pancreas (4) tumors who had FDG-PET-CT for target delineation prior to EBRT were studied. Patients were selected among the group that showed respiratory-induced tumor motion 〉5mm. 4D-PET was performed by means of a Philips Gemini BigBore scanner, using the Varian RPM gating system. An identical system was available at the linac for treatment. The breathing cycle was equally divided in 4 phases, according to a previous study. Since planning was made on a single CT-phase, no ITV was explicitly built from the set of phases. The BTV was identified with SUV=2.2 threshold and the PTV was obtained expanding the BTV by 8mm(S-I), 5mm(A-P) and 3mm(L-R) to account for residual motion and setup errors. The most advantageous CT-phase for treatment planning was then identified by simulating plans on each phase and analyzing the resulting DVHs of OARs (lung, trachea, oesophagus, spinal cord, left ventricle).
The observed maximum range of motion was 5.5mm(L-R), 12.3mm(A-P) and 19.2mm(S-I). The standard deviation of the BTV volume in the 4 phases ranged from 6% to 13.7%. V20 (lung) ranged 7.1%-15.2% in inspiration and 7.8%-18.6% in expiration. The mean dose to the oesophagus ranged 0.1-2.2Gy in inspiration and 1.4-2.0Gy in expiration. In general, the dose to OARs was smaller when planning on a single phase than on the overall, respiratory-uncontrolled volume (p-value〈0.05).
The BTV volume was almost constant between phases, confirming that the motion might be described by 4 phases. There was no obvious choice of the optimal phase for treatment planning, suggesting patient-by-patient studies. However, planning and delivery on one phase consistently allowed dose sparing to be obtained compared to non-gated techniques.
为在接受呼吸门控放射治疗的肿瘤靶区勾画中使用呼吸门控PET（4D-PET）寻找一种优化的工作流程。
研究了15例在立体定向放射治疗（EBRT）前进行FDG-PET-CT以勾画靶区的肺（11例）和胰腺（4例）肿瘤患者。患者从显示呼吸诱导肿瘤运动＞5mm的组中选取。4D-PET通过飞利浦Gemini大孔径扫描仪，使用瓦里安RPM门控系统进行。直线加速器上有相同的系统用于治疗。根据先前的研究，呼吸周期平均分为4个阶段。由于计划是在单个CT阶段进行的，因此未从各阶段集合中明确构建内部靶区（ITV）。以SUV=2.2为阈值确定生物学靶区（BTV），并通过将BTV在头脚方向（S-I）扩展8mm、前后方向（A-P）扩展5mm和左右方向（L-R）扩展3mm来获得计划靶区（PTV），以考虑残余运动和摆位误差。然后通过在每个阶段模拟计划并分析危及器官（肺、气管、食管、脊髓、左心室）的剂量体积直方图（DVH）来确定治疗计划最有利的CT阶段。
观察到的最大运动范围为左右方向5.5mm、前后方向12.3mm和头脚方向19.2mm。4个阶段中BTV体积的标准差范围为6%至13.7%。肺的V20在吸气时范围为7.1%-15.2%，呼气时范围为7.8%-18.6%。食管的平均剂量在吸气时范围为0.1-2.2Gy，呼气时范围为1.4-2.0Gy。一般来说，在单个阶段进行计划时，危及器官的剂量比在整个呼吸未控制体积上进行计划时要小（p值＜0.05）。
各阶段之间BTV体积几乎恒定，证实运动可用4个阶段来描述。在治疗计划的最佳阶段没有明显的选择，建议进行个体化研究。然而，与非门控技术相比，在一个阶段进行计划和实施始终能够实现剂量 sparing。
