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放疗及放化综合治疗是不可切除性食管癌的主要治疗手段,目前,放疗计划的制定主要依靠常规影像学,而常规影像学提供的仅仅是解剖形态学信息,不能提供肿瘤生物活性信息,这使放疗计划制定的准确率受到限制。PET/CT将PET及CT两种影像学技术有机融合,一次扫描可同时获得功能代谢图像和解剖形态图像,为精确放疗的靶区勾画提供了新武器。PET/CT最常用的显像剂为18F-FDG。本文将主要对18F-FDG PET/CT在食管癌放疗前分期、放疗靶区的勾画、疗效监测及预后评估等方面的应用及存在的问题进行探讨。
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PET/CT用于放疗靶区的勾画是国内外研究的热点,许多学者对PET/CT在食管癌放疗靶区勾画中的应用进行了研究(表 1)。Gondi等[15]比较了16例食管癌患者在CT和PET/CT检查下的大体肿瘤体积(gross target volume,GTV),结果发现:PET/CT使62.5%(10/16)患者的GTV缩小超过5%,作者还计算出适形指数(conformality index,CI),若CI=1.00,提示CT和PET/CT检查下的GTV一致;若CI=0.00,则提示二者完全不同。该研究中CI=0.46,证明使用CT和PET/CT勾画GTV存在明显差异,作者分析可能与入组病例中大部分患者为食管下段癌有关,CT对此区域病变的分辨能力弱,而PET/CT则不受病变位置的影响。郭洪波等[14]回顾性地分析了30例食管癌患者,13例由CT确定的淋巴结GTV与病理结果一致,19例基于PET/CT的淋巴结GTV和病理结果相符,PET/CT改变了15例由CT确定的淋巴结GTV,导致3例淋巴结GTV缩小,12例淋巴结GTV增大。PET/CT确定淋巴结GTV的准确率高于CT(67% vs. 25%)。
研究者 时间 例数 靶区勾画方法 GTV减少比例(%) GTV增加比例(%) GTV改变总比例(%) PET及PET/CT对治疗计划影响 Moureau-Zabotto等[13] 2005 34 肉眼法 12/34(35) 7/34(21) 19/34(56) PET/CT使56%患者GTV改变,53%患者PTV改变 郭洪波等[14] 2007 30 肉眼法 3/30(10) 12/30(40) 15/30(50) PET/CT发现转移淋巴结的效能优于CT,使患者GTV扩大 Gondi等[15] 2007 16 肉眼法 10/16(63) - 10/16(63) PET/CT使63%患者GTV改变,推荐用适形指数评价其与CT勾画的差异 Hong等[16] 2008 25 ①肉眼法
②半自动法- - ①21/25(84)
②14/25(56)无论是对原发肿瘤还是远处淋巴结转移,PET/CT能提供更丰富的临床信息 Muijs等[17] 2009 21 肉眼法 9/21(43) 3/21(14) 12/21(57) CT可能排除部分PET阳性病变,PET/CT可导致正常组织受照剂量改变 Schreurs等[18] 2010 28 肉眼法 17/28(61) 11/28(39) 28/28(100) PET/CT可在不改变观察者之间差异的同时改变靶区 注:表中,GTV:大体肿瘤体积;PTV:计划靶区;“原”表示文中未提供明确数据。 表 1 PET/CT在食管癌放疗靶区勾画中的应用研究
不同的研究采用PET/CT勾画靶区的方法不同,其推荐的最佳勾画方法见表 2。有研究发现用PET/CT定位和勾画靶区,与单纯CT相比,可减小正常组织如肺、心脏、脊髓等的受照剂量[13]。目前,PET/CT在食管癌放疗靶区勾画中的应用均是小样本量研究,采用何种方法勾画靶区最佳,是否优于单纯CT,是否符合实际病变范围,尚无明确定论,有待大样本研究证实。
研究者 时间 例数 勾画方法 结论 Zhong等[19] 2009 33 ①肉眼法②SUV2.5③40%SUVmax PET评价肿瘤大小的最佳方法随肿瘤长度和SUVmax的变化而变化,SUV2.5为最佳阈值 Yu等[20] 2009 16 4种SUV阈值法* 以SUVbgd+20%为阈值勾画靶区,可能是最能准确反映肿瘤原发灶信息的方法 Han等[21] 2010 22 ①肉眼法②SUV2.5③40%SUVmax 最接近食管癌病理长度的阈值是SUV2.5 Jeganathan等[22] 2011 87 ①肉眼法②SUV2.5 PET/CT勾画靶区的准确率高,肉眼法优于SUV2.5阈值法 注:表中,*:分别以SUVbgd+20%、SUVbgd+40%、SUV2.5、40%SUVmax为阈值自动勾画确定病变长度和外侵范围,其中,SUVmax:最大标准化摄取值,SUVbgd:本底平均标准化摄取值。 表 2 PET/CT在食管癌靶区勾画中的最佳方法研究
18F-FDG PET/CT在食管癌放疗中的应用
The application of 18F-FDG PET/CT in the radiotherapy of esophageal cancer
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摘要: 随着三维适形和调强放疗技术的发展,放射治疗成为食管癌的重要治疗手段之一。准确的肿瘤分期和精确的靶区勾画是食管癌精确放疗成功的先决条件。常规影像在指导食管癌精确放疗计划、早期疗效监测以及检测肿瘤复发中有很大帮助,但仍存在许多局限性。PET/CT作为一种功能与解剖的融合影像,可以弥补传统影像的某些不足,在食管癌的诊治中发挥着越来越重要的作用。该文将主要对18F-FDG PET/CT在食管癌放疗前分期、放疗靶区勾画、疗效监测及预后评估等方面的应用进行探讨。Abstract: With the development of three dimensional conformal radiotherapy and intensity modulated radiotherapy, radiotherapy becomes an important treatment for esophageal cancer. Accurate staging and target volume delineation are prerequisites for a successful treatment of esophageal cancer with radiotherapy. Conventional cross-sectional images are helpful for guiding radiotherapy plans, assessing treatment response and detecting recurrence. But there are still many limitations for anatomic information alone. PET/CT is an imaging fusion modality which may overcome some limitations of conventional cross-sectional modalities. It plays an important role in the diagnosis and treatment of esophageal cancer. This review evaluates the applications of 18F-FDG PET/CT in the initial staging before radiotherapy, its target volume definition, treatment response and the prognosis of esophageal cancer.
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表 1 PET/CT在食管癌放疗靶区勾画中的应用研究
研究者 时间 例数 靶区勾画方法 GTV减少比例(%) GTV增加比例(%) GTV改变总比例(%) PET及PET/CT对治疗计划影响 Moureau-Zabotto等[13] 2005 34 肉眼法 12/34(35) 7/34(21) 19/34(56) PET/CT使56%患者GTV改变,53%患者PTV改变 郭洪波等[14] 2007 30 肉眼法 3/30(10) 12/30(40) 15/30(50) PET/CT发现转移淋巴结的效能优于CT,使患者GTV扩大 Gondi等[15] 2007 16 肉眼法 10/16(63) - 10/16(63) PET/CT使63%患者GTV改变,推荐用适形指数评价其与CT勾画的差异 Hong等[16] 2008 25 ①肉眼法
②半自动法- - ①21/25(84)
②14/25(56)无论是对原发肿瘤还是远处淋巴结转移,PET/CT能提供更丰富的临床信息 Muijs等[17] 2009 21 肉眼法 9/21(43) 3/21(14) 12/21(57) CT可能排除部分PET阳性病变,PET/CT可导致正常组织受照剂量改变 Schreurs等[18] 2010 28 肉眼法 17/28(61) 11/28(39) 28/28(100) PET/CT可在不改变观察者之间差异的同时改变靶区 注:表中,GTV:大体肿瘤体积;PTV:计划靶区;“原”表示文中未提供明确数据。 表 2 PET/CT在食管癌靶区勾画中的最佳方法研究
研究者 时间 例数 勾画方法 结论 Zhong等[19] 2009 33 ①肉眼法②SUV2.5③40%SUVmax PET评价肿瘤大小的最佳方法随肿瘤长度和SUVmax的变化而变化,SUV2.5为最佳阈值 Yu等[20] 2009 16 4种SUV阈值法* 以SUVbgd+20%为阈值勾画靶区,可能是最能准确反映肿瘤原发灶信息的方法 Han等[21] 2010 22 ①肉眼法②SUV2.5③40%SUVmax 最接近食管癌病理长度的阈值是SUV2.5 Jeganathan等[22] 2011 87 ①肉眼法②SUV2.5 PET/CT勾画靶区的准确率高,肉眼法优于SUV2.5阈值法 注:表中,*:分别以SUVbgd+20%、SUVbgd+40%、SUV2.5、40%SUVmax为阈值自动勾画确定病变长度和外侵范围,其中,SUVmax:最大标准化摄取值,SUVbgd:本底平均标准化摄取值。 -
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