^18F-FDG PET/CT勾画鼻咽癌原发肿瘤体积最适阈值的研究

The suitable uptake value threshold of ^18F-FDG PET/CT image on gross tumor volume delineation of nasopharyngeal carcinoma

目的寻找^18F-FDG PET/CT勾画鼻咽癌大体肿瘤体积（GTV）的最适阈值.方法 16例初诊鼻咽癌患者在治疗前接受^18F-FDG PET/CT及MRI检查,将MRI/CT融合图像上勾画的肿瘤GTV定义为GTVf,^18F-FDG PET/CT勾画肿瘤范围为BTV.不同阈值条件下的BTV通过调整最大标准摄取值（SUVmax）的比例得到.将不同阈值条件下的BTV和GTVf进行比较,当二者在体积及形态学上达到最佳匹配时对应的阈值水平为最适阈值（sTL）.sTL×SUVmax得到相应的最适标准摄取值（sSUV）.结果 16例患者最适阈值sTL（％）为20.93 ±6.51,相应的最适标准摄取值sSUV为2.27±0.48.sTL与SUVmax呈负相关（R^2=0.85,F=78.57,P＜0.05）;sSUV与SUVmax呈正相关（R^2 =0.75,F=41.88,P＜0.05）;sTL与GTVf无相关性.结论利用SUVmax阈值法勾画鼻咽癌GTV是可行的,最适阈值不是一个固定数值,与SUVmax相关,与肿瘤体积没有明显相关性.

Objective To define a suitable threshold setting for gross tumor volume （GTV）when using ^18F-fluoro-deoxyglucose positron emission tomography and computed tomogram （PET/CT） for radiotherapy planning in Nasopharyngeal carcinoma（NPC）.Methods Sixteen NPC patients respectively received PET/CT and MRI scan before their radiation treatment.All of the images were transferred to the radiotherapy planning system （TPS）.MRI/CT-based primary GTV was defined as GTVf.Biological target volumes （BTVs） were derived from PET/CT-based GTVs of primary tumors.The BTVs were defined as the volumes when adjusting different percentage of the maximal standardized uptake value （SUVmax）.GTVfs were compared with BTVs.The suitable threshold level （sTL） could be determined when BTV value and its morphology using a certain threshold level were observed to be the fittest GTVf.The suitable standardized uptake value （sSUV） was calculated as the sTL multiplied by the SUVmax.Results Our result demonstrated no single sTL or sSUV method could achieve an optimized volumetric match with the GTVf.The sTL was [20.93%±6.51%（15%-40%）],whereas the sSUV was [2.27±0.48（1.56-3.25）].The sTL was inversely correlated with the SUVmax sTL =-0.144ln（SUVmax） ＋ 0.5548 （R^2 =0.85,F =78.57,P〈0.01.The sSUV showed a linear correlation with the SUVmax sSUV =0.104（SUVmax） ＋ 1.0398,（R^2=0.75,F=41.88,P〈0.01）.The sTL was not associated with the value of GTVf.Conclusions In PET/CT-based BTV for NPC,SUVmax threshold method is feasible.sTL is not a fixed value,which is correlated with the SUVmax instead of the value of tumor.