Nestle Ursula, Kremp Stephanie, Schaefer-Schuler Andrea, Sebastian-Welsch Christiane, Hellwig Dirk, Rübe Christian, Kirsch Carl-Martin
Department for Nuclear Medicine, Saarland University Medical Center, Homburg/Saar, Germany.
J Nucl Med. 2005 Aug;46(8):1342-8.
PET with (18)F-FDG ((18)F-FDG PET) is increasingly used in the definition of target volumes for radiotherapy, especially in patients with non-small cell lung cancer (NSCLC). In this context, the delineation of tumor contours is crucial and is currently done by different methods. This investigation compared the gross tumor volumes (GTVs) resulting from 4 methods used for this purpose in a set of clinical cases.
Data on the primary tumors of 25 patients with NSCLC were analyzed. They had (18)F-FDG PET during initial tumor staging. Thereafter, additional PET of the thorax in treatment position was done, followed by planning CT. CT and PET images were coregistered, and the data were then transferred to the treatment planning system (PS). Sets of 4 GTVs were generated for each case by 4 methods: visually (GTV(vis)), applying a threshold of 40% of the maximum standardized uptake value (SUV(max); GTV(40)), and using an isocontour of SUV = 2.5 around the tumor (GTV(2.5)). By phantom measurements we determined an algorithm, which rendered the best fit comparing PET with CT volumes using tumor and background intensities at the PS. Using this method as the fourth approach, GTV(bg) was defined. A subset of the tumors was clearly delimitable by CT. Here, a GTV(CT) was determined.
We found substantial differences between the 4 methods of up to 41% of the GTV(vis). The differences correlated with SUV(max), tumor homogeneity, and lesion size. The volumes increased significantly from GTV(40) (mean 53.6 mL) < GTV(bg) (94.7 mL) < GTV(vis) (157.7 mL) and GTV(2.5) (164.6 mL). In inhomogeneous lesions, GTV(40) led to visually inadequate tumor coverage in 3 of 8 patients, whereas GTV(bg) led to intermediate, more satisfactory volumes. In contrast to all other GTVs, GTV(40) did not correlate with the GTV(CT).
The different techniques of tumor contour definition by (18)F-FDG PET in radiotherapy planning lead to substantially different volumes, especially in patients with inhomogeneous tumors. Here, the GTV(40) does not appear to be suitable for target volume delineation. More complex methods, such as system-specific contrast-oriented algorithms for contour definition, should be further evaluated with special respect to patient data.
正电子发射断层显像（PET）联合（18）F - 氟脱氧葡萄糖（（18）F - FDG PET）越来越多地用于放射治疗靶区体积的定义，尤其是在非小细胞肺癌（NSCLC）患者中。在此背景下，肿瘤轮廓的勾画至关重要，目前有不同的方法。本研究比较了在一组临床病例中用于此目的的4种方法所得到的大体肿瘤体积（GTV）。
分析了25例NSCLC患者原发肿瘤的数据。他们在初始肿瘤分期时有（18）F - FDG PET检查。此后，在治疗体位进行胸部额外的PET检查，随后进行计划CT扫描。CT和PET图像进行配准，然后将数据传输到治疗计划系统（PS）。通过4种方法为每个病例生成4组GTV：视觉勾画（GTV（vis））、应用最大标准化摄取值（SUV（max））40%的阈值（GTV（40））以及使用肿瘤周围SUV = 2.5的等剂量线（GTV（2.5））。通过模体测量我们确定了一种算法，该算法在PS中使用肿瘤和背景强度将PET与CT体积进行最佳拟合比较。将此方法作为第四种方法，定义GTV（bg）。一部分肿瘤可通过CT清晰界定。在此，确定GTV（CT）。
我们发现4种方法之间存在显著差异，相差可达GTV（vis）的41%。这些差异与SUV（max）、肿瘤同质性和病变大小相关。体积从GTV（40）（平均53.6 mL）< GTV（bg）（94.7 mL）< GTV（vis）（157.7 mL）和GTV（2.5）（164.6 mL）显著增加。在不均匀病变中，GTV（40）导致8例患者中有3例在视觉上肿瘤覆盖不足，而GTV（bg）导致的体积处于中间水平，更令人满意。与所有其他GTV不同，GTV（40）与GTV（CT）不相关。
在放射治疗计划中，通过（18）F - FDG PET进行肿瘤轮廓定义的不同技术导致体积有显著差异，尤其是在肿瘤不均匀的患者中。在此，GTV（40）似乎不适用于靶区体积的勾画。更复杂的方法，如针对系统的基于对比度的轮廓定义算法，应结合患者数据进一步评估。
