^18F-FDG PET／CT引导局部晚期非小细胞肺癌靶区剂量提升的可行性研究

The study of the feasibility of dose escalation guided by ^18F-FDG PET/CT for high metabolic region in radiotherapy of locally advanced non-small cell lung cancer

目的 研究基于放疗前正电子发射计算机断层显像（PET/CT）的标准摄取值（SUV）梯度引导局部晚期非小细胞肺癌（NSCLC）患者靶向剂量提升的可行性及剂量学特点.方法 收集29例NSCLC患者的放疗前PET/CT图像,在PET/CT图像上勾画大体肿瘤靶区（GTV）,以最大SUV值（SUVmax）的50%和75%为阈值将GTV分割为3个代谢活性亚区域,低于50%SUVmax的区域为GTV1,50%SUVmax到75%SUVmax的区域为GTV2,高于75%SUVmax的区域为GTV3.计划靶区（PTV）、PTV1、PTV2、PTV3分别由GTV、GTV1、GTV2及GTV3外放适当边界得到.计划1：在PTV上照射均匀60 Gy处方剂量.计划2：将PTV1、PTV2和PTV3的处方剂量分别设置为60-66 Gy、66-72 Gy和≥72 Gy.比较两种治疗计划靶区和危及器官（OAR）的剂量学差异.结果 相对于计划1,计划2将2%的PTV体积接受的剂量（D2）由66.5 Gy提升至78.5 Gy,剂量提升约20%;PTV的平均剂量提升了8.9%（63.2-68.8 Gy）、PTV1,PTV2、PTV3的平均剂量分别提升了2.8%（62.7-64.4 Gy）、10.3%（63.5-70.0 Gy）、18.7%（63.8-75.8 Gy）.各亚区域剂量均得到有效提升.计划1与计划2中PTV的60 Gy剂量线靶区覆盖度基本相当,差异无统计学意义（P〉0.05）,均匀性指数（HI）的差异有统计学意义（t=23.3,P〈0.05）,计划2中随着最大剂量的提升,HI下降显著.肺、心脏和脊髓的受照剂量在两个治疗计划中基本相当,差异均无统计学意义（P〉0.05）.结论 对不同代谢活性梯度实施差异化的放疗剂量,在不增加危及器官辐射剂量的前提下,可对代谢活性高的亚区域进行靶向剂量提升,具有提高肿瘤局部控制的潜能.

Objective To investigate dose escalation by metabolic sub-volume based on standard uptake values （ SUV） gradient of pre-treatment positron emission tomography/computed tomography （ PET/CT） for locally advanced non-small cell lung cancer （ NSCLC） radiotherapy. Methods The pre-treatment 18 F-FDG PET/CT images of 29 patients with locally advanced NSCLC were analyzed retrospectively. Gross tumor volume （ GTV） was delineated on the PET/CT fusion images. Tumor metabolic sub-volume was segmented according to the threshold of 50% and 75% maximum standard uptake values （ SUVmax ） . The region that under 50% SUVmax was defined as GTV1. From 50% to 75% SUVmax was defined as GTV2,and over 75% SUVmax was defined as GTV3. PTV （planning target volume）, PTV1, PTV2 and PTV3 were extended from GTV, GTV1, GTV2 and GTV3, and different plans were designed subsequently. Plan 1 was designed for PTV with prescription dose 60 Gy, and Plan 2 was designed for PTV1, PTV2 and PTV3 with prescription dose 60-66 Gy, 66-72 Gy and≥72 Gy, respectively. The dosimetric parameters between tumor target and organs at risk （OARs） were compared. Results Compared to Plan 1, the absorbed dose in Plan 2 that covers 2% volume of the PTV （ D2 ） was increased from 66. 5 Gy to 78. 5 Gy and the dose was escalated by about 23. 2%. The average dose of PTV1, PTV2 and PTV3 increased by 2. 8% （62. 7-64. 4 Gy）, 10. 3% （63. 5 -70. 0 Gy）, 18. 7% （63. 8 -75. 8 Gy）, and the average dose of PTV increased by 8. 9% （63. 2-68. 8 Gy）. The sub-regional dose had been effectively improved. There was no significant difference in target coverage between Plan 1 and Plan 2 （ P 〉0. 05 ） . Homogeneity index （HI） was decreased with the escalation of maximum dose for Plan 2（t=23. 3, P〈0. 05）. There was no statistically significant difference in radiation dose of OARs between two plans （ P〉0. 05 ） . Conclusions Dose escalation based on metabolic sub-volume from 18 F-FDG PET/CT was feasible, and radiation dose escalation of sub-volume with high metabolic activity can be achieved without increasing the OARs dose.