PET-CT同机融合精度验证及在放疗靶区勾画中的应用

目的验证PET-CT同机融合的精度并实际应用于患者，为放疗的PET-CT定位及靶区勾画提供临床依据。方法用不同浓度的^18FDG灌注体模上的标志点和不同尺寸的圆柱体，PET和CT以层厚4mm扫描后的影像传输至eNTEGRA工作站和放疗计划系统(TPS)工作站，进行图像融合和三维重建，在PET和CT影像上测量标志点之问的距离和PET-CT的融合误差。用扣除一定比例像素值的方法测量圆柱体的PET影像体积和CT影像体积，并把两者进行比较，同样的方法应用于10例非小细胞肺癌患者的10个肿瘤体积测量。结果eNTEGRA和TPS工作站有良好的长度线性，但后者的图像融合误差明显大于前者。不同体积肿瘤、不同浓度^18FDG需采用不同的像素值扣除比例。圆柱体和10个肿瘤PET影像体积和CT影像体积有较好的一致性。结论PET—CT同机融合的精度完全符合放疗的临床要求，扣除一定比例像素值的方法可用于PET影像的肿瘤范围的勾画。     

18F-脱氧葡萄糖PET不同阈值法勾画非小细胞肺癌靶区的比较研究

目的 探讨不同标准摄取值(SUV)阈值法下,18F-脱氧葡萄糖(18FDG)PET影像勾画非小细胞肺癌GTV的差异.方法 20例患者行18FDG PET扫描,比较阈值法(42%阈值)PET图像GTV(GTV42%)、相对阈值法[(threshold SUV=0.307×mean target SUV+0.588)/maximun SUV] PET图像GTV(GTVrelate)及CT图像GTV(GTVCT)的大小.结果 GTV42%为(13812.5±13 841.4)mm3,GTVrelate为(24 325.3±22 454.7)mm3,GTVCT为(28 350.9±26 079.8)mm3.GTV42%、GTVrelate及GTVCT之间差异有统计学意义(F=17.10,P＜0.01).GTV42%明显小于GTVrelate和GTVcT(P值均＜0.01),GTVrelate与GTVCT差异无统计学意义(P=0.125).结论 使用相对阈值法勾画靶区,其精确度优于固定阈值法(42%阈值),能较好地反映肿瘤真实体积.     

三种阈值下勾画非小细胞肺癌PET图像靶区及影响的研究

目的 比较不同阈值对18FDG PET-CT图像中非小细胞肺癌靶区勾画及放疗计划可能产生的影响.方法 选择CT图像上原发灶边界清楚的、呼吸动度≤5 mm的非小细胞肺癌8例,注射18FDG后1 h行PET扫描并以CT图像作衰减校正.以CT图像勾画的大体肿瘤体积(GTVCT)为标准,比较PET图像上用3种阈值条件[即肿瘤内最大像素值的42%(42%Imax(total))、本底平均像素值+肿瘤内最大像素值与本底平均像素值的差值的20%(Iback+20%Imax-back(max))和本底平均像素值+肿瘤内每层最大像素值与本底平均像素值的差值的20%(Iback+20%Imax-back(slice))]勾画的GTV(计为GTV42%、GTV20%max和GTV20%slice)与GTVCT差异及对GTVCT覆盖率的差异.以GTVCT、GTV42%、GTV20%max、GTV20%slice三维外放1 cm为计划靶体积,分别计为PTVCT、PTV42%、PTV20%max、PTV20%slice.对不同PTV设计三维适形放疗计划,并均给予靶区剂量66 Gy分33次6.6周完成.比较以不同PTV设计的计划中,PTVCT内接受＜95%处方剂量的体积(VPTV)及肺V20,并推算可能产生的TCP和肺NTCP的差异.结果 GTV42%、GTV20%max、GTV20%slice与GTVCT的中位体积差分别为-54.1%,-21.5%和5.3%,三者对GTVCT的覆盖率中位数分别为45.9%、78.0%和95.3%(F=57.50,P＜0.01).以不同PTV设计放疗计划时,PTV42%的中位VPTV为7.5%,由此可能导致TCP中位下降1%.PTV20%max和PTV20%slice的中位VPTV分别为1.3%和0.0%,其TCP与PTVCT的相似,与PTV42%的不同.三者的肺V20和肺NTCP与PTVCT的相似.结论 层面化阈值条件Iback+20%Imax-back(slice)可能是PET图像用于肺癌靶区勾画的较准确阈值,该阈值不依赖于预先由CT提供的肿瘤体积信息,可望用于伴有肺不张的非小细胞肺癌的靶区勾画.     

PET/CT对非小细胞肺癌三维适形放疗中治疗计划参数的影响

目的:观察PET/CT对非小细胞肺癌(NSCLC)三维适形放疗(3D-CRT)中治疗计划参数的影响.方法:对83例在PET/CT定位下拟行根治性3D-CRT的NSCLC患者,分别以CT图像和PET/CT融合图像勾画大体肿瘤靶区(GTVCT和GTVPET/CT),分别制定放疗计划,并对两者进行比较.结果:PET/CT明显改变44例(53.01％)患者GTV或PTV,31例PTV和(或)GTV减小,13例PTV和(或)GTV增加.根据PET/CT和CT分别制定的放疗计划在VGTV、VE50、SCM和ESM的差异有统计学意义,P值分别为0.001、0.001、0.000和0.002.结论:应用PET/CT制定NSCLC3D-CRT治疗计划可降低食管和脊髓的受照射剂量,从而有利于放疗剂量的提升.     

肺癌患者GTVPET-CT勾画的系统分析

目的分析肺癌患者GTVPET-CT的勾画、阈值的选择,以及同机和非同机融合靶区的差异。方法在PUBMED和EMBASE中检索用PET-CT融合图像为肺癌患者勾画靶区的现有研究。回顾和分析靶区勾画方法,并对同机和非同机融合GTVPET-CT进行分析。结果文献检索中,共有10篇文献满足研究条件。10项研究总共有198例,其中非同机融合研究153例（77．3%）,同机融合45例（23．7%）。其中,4篇有详细GTV数据的文献共有79例,同机和非同机融合研究的GTVPET-CT分别为（88．0±93．0）cm^3和（59．1±77．9）cm^3。同机融合和非同机融合间GTV绝对差/绝对和差异有统计学意义（t=-6．55,P＜0．001）。即使把Brianzoni（同机融合）的绝对差/绝对和,与其一致性较好的Steenbakkers（非同机融合）单独比较时,差异仍有统计学意义（t=-3．27,P=0．003）。结论与非同机融合相比,同机融合PET-CT图像有更小的器官位移,更适用于靶区的勾画。放疗的靶区勾画方法应首选40%～50%范围的可变阈值,并且选取与肺窗CT靶区相应的阈值。     

非小细胞肺癌合并肺不张三维适形放疗靶区确定的方法学研究

目的探讨非小细胞肺癌（NSCLC）合并肺不张三维适形放疗（3DCRT）时大体肿瘤靶区（GTV）的确定方法。方法对19例经病理学检查确诊为非小细胞肺癌且CT检查合并肺不张患者，先后在同一体位和胸部热塑膜固定下行胸部CT—SIM扫描和胸部（全身）18F—FDGPET／CT检查，分别勾画大体肿瘤体积CT-GTV和18F-FDGPET／CT-GTV（PET-GTV），并由治疗计划系统给出GTV体积的具体数字加以比较。结果全部患者的CT—GTV和PET-GTV均有不同程度的差异，其中3例患者的PET-GTV较CT—GTV增加20．1％（31．7cm^3），CT-GTV平均为144cm^3（129～156cm^3），PET-GTV平均为173cm^3（152～188cm^3）；16例患者的PET-GTV较CT-GTV减少29％（27．2cm^3），CT-GTV平均为138cm^3（95～190cm^3），PET-GTV平均为126cm^3（60～160cm^3）（P〈0．05）。GTV的减少主要原因是PET显像除外了因肿瘤原因造成的肺不张，从而引起靶区范围的缩小，使靶区更加精确，且避免周围正常组织不必要的照射，最大限度地保护了正常组织，显示3DCRT的优点。结论18F—FDGPET／CT显像对于非小细胞肺癌合并肺不张患者的肺不张组织与局部病变有一定的鉴别意义，提高了靶区定位的精确性。     

PET-CT在局部晚期非小细胞肺癌调强放疗中的应用

目的 探讨PET-CT对局部晚期非小细胞肺癌（NSCLC）临床分期的诊断及其融合图像下勾画靶区对调强放疗计划的影响。方法 对13例局部晚期NSCLC患者同一体位分别进行增强CT和PET同机扫描,图像重建后传输至三维治疗计划系统（3D-TPS）进行自动图像融合。PET-CT下诊断患者的分期;分别在CT、PET-CT融合图像上勾画靶区,设计放疗计划。患者均采用5野调强放疗,常规处方剂量60Gy／30f。比较两个计划的V20、全肺平均受量（MLD）、心脏平均受量、脊髓最大受量。结果 5例患者分期改变：3例升高,2例下降;CT下勾画靶区GTV、PTV分别为（159.35±84.44）cm3 、（442.12±172.57）cm3,显著高于PET-CT下勾画的GTV和PTV［（148.22±75.08）cm3 、（428.64±157.91）cm3］; PET CT下计划的全肺V20、MLD、心脏平均受量、脊髓最大受量等各项剂量学参数均优于CT下的计划（P＜0.05）。结论 PET-CT较CT更有利于局部晚期NSCLC放疗靶区的勾画,可以更好地保护周围正常组织和器官。     

PET-CT对非小细胞肺癌精确放疗靶区勾画的影响

目的 探讨正电子发射体层显像(PET)与cT同机融合图像(PET-CT)对非小细胞肺癌(NSCLC)大体肿瘤靶区(GTV)勾画的影响.方法 选取46例具有典型影像表现的NSCLC患者的PET-CT资料,根据其影像学特点将所有病例分为3组,肺不张组16例,纵隔和(或)肺门淋巴结转移组18例,外周型单纯肺内病灶组12例.根...     

FDG PET对非小细胞肺癌合并肺不张三维适形放疗时靶区确定的临床意义

目的 探讨^18F-脱氧葡萄糖（FDG）PET对合并肺不张的非小细胞肺癌（NSCLC）行三维适形放疗时病变靶区确定的临床意义。方法 对14例经病理组织学证实为NSCLC且其影像学检查伴有不同程度肺不张者，先后行胸部增强明扫描及胸部或全身FDGP盯肿瘤显像。根据扫描及显像结果勾画原发病灶范围，分别称为CT-GTV和PET-GTV，并由CMS治疗计划系统给出GTV体积的具体数值加以比较。结果 全部患者的CT-GTV与PET-GTV均有不同程度差别，其中1例患者PET-GTV较CT-GTV增加16．9％（22cm^3），CT-GTV为130cm3，PET-G11V为152cm^3；13例患者PET-GTV较CT-GTV平均减少20．4％（27．2cm^3），CT-GTV平均为133cm^3（90-180cm^3），PET-GTV平均为106cm^3（60—153cm^3）（P=0．000）。GTV的减少主要原因是PET显像除外了因肿瘤原因造成的肺不张，从而引起靶区范围的缩小，进而避免对周围正常组织（主要是正常或不张的肺组织、脊髓及心血管）的不必要照射，最大限度地保护了正常组织。结论 FDG PET在确定肺不张与局部病变相互关系方面具有一定临床价值，并由此提高了靶区定位的精确性。     

PET-CT在非小细胞肺癌治疗中的应用

正电子发射体层显像(PET)-CT融合了解剖图像和功能代谢图像,诊断的敏感性、特异性、准确性比PET显著提高。现分析PET-CT在非小细胞肺癌患者治疗方案制定中的应用及对治疗方案产生的影响。     

Practical integration of [18F]-FDG-PET and PET-CT in the planning of radiotherapy for non-small cell lung cancer (NSCLC): the technical basis, ICRU-target volumes, problems, perspectives.

The value of positron emission tomography using [18F]-fluoro-deoxy-glucose (FDG-PET) for pretherapeutic evaluation of patients with non-small cell lung cancer (NSCLC) is beyond doubt. Due to the increasing availability of PET and PET-CT scanners the method is now widely available, and its technical integration has become possible for radiotherapy planning systems. Due to the depiction of malignant tissue with high diagnostic accuracy, the use of FDG-PET in radiotherapy planning of NSCLC is very promising. However, by uncritical application, PET could impair rather than improve the prognosis of patients. Therefore, in the present paper we give an overview of technical factors influencing PET and PET-CT data, and their consequences for radiotherapy planning. We further review the relevant literature concerning the diagnostic value of FDG-PET and on the integration of FDG-PET data in RT planning for NSCLC. We point out the possible impact in gross tumor volume (GTV) definition and describe methods of target volume contouring of the primary tumor, as well as concepts for the integration of diagnostic information on lymph node involvement into the clinical target volume (CTV), and the possible implications of PET data on the definition of the planning target volume (PTV). Finally, we give an idea of the possible future use of tracers other than [18F]-FDG in lung cancer.     

The impact of (18)F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) lymph node staging on the radiation treatment volumes in patients with non-small cell lung cancer.

PURPOSE: (18)F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) combined with computer tomography (PET-CT) is superior to CT alone in mediastinal lymph node (LN) staging in non-small cell lung cancer (NSCLC). We studied the potential impact of this non-invasive LN staging procedure on the radiation treatment plan of patients with NSCLC. PATIENTS AND METHODS: The imaging and surgical pathology data from 105 patients included in two previously published prospective LN staging protocols form the basis for the present analysis. For 73 of these patients, with positive LN's on CT and/or on PET, a theoretical study was performed in which for each patient the gross tumour volume (GTV) was defined based on CT and on PET-CT data. For each GTV, the completeness of tumour coverage was assessed, using the available surgical pathology data as gold standard. A more detailed analysis was done for the first ten consecutive patients in whom the PET-CT-GTV was smaller than the CT-GTV. Theoretical radiation treatment plans were constructed based on both CT-GTV and PET-CT-GTV. Dose-volume histograms for the planning target volume (PTV), for the total lung volume and the lung volume receiving more than 20 Gy (V(lung(20))), were calculated. RESULTS: Data from 988 assessed LN stations were available. In the subgroup of 73 patients with CT or PET positive LN's, tumour coverage improved from 75% when the CT-GTV was used to 89% with the PET-CT-GTV (P=0.005). In 45 patients (62%) the information obtained from PET would have led to a change of the treatment volumes. For the ten patients in the dosimetry study, the use of PET-CT to define the GTV, resulted in an average reduction of the PTV by 29+/-18% (+/-1 SD) (P=0.002) and of the V(lung(20)) of 27+/-18% (+/-1 SD) (P=0.001). CONCLUSION: In patients with NSCLC considered for curative radiation treatment, assessment of locoregional LN tumour extension by PET will improve tumour coverage, and in selected patients, will reduce the volume of normal tissues irradiated, and thus toxicity. This subgroup of patients could then become candidates for treatment intensification.     

Impact of computed tomography (CT) and 18F-deoxyglucose-coincidence detection emission tomography (FDG-CDET) image fusion for optimisation of conformal radiotherapy in non-small-cell lung cancers]

To report a retrospective study concerning the impact of fused 18F-fluorodeoxy-D-glucose (FDG)-hybrid positron emission tomography (PET) and computed tomography (CT) images on three-dimensional conformal radiation therapy (3D-CRT) planning for patients with non-small-cell lung cancer (NSCLC). PATIENTS AND METHODS: One hundred and one patients consecutively treated for stages I-III NSCLC were studied. Each patient underwent CT and FDG-hybrid PET for simulation treatment in the same radiation treatment position. Images were coregistered using five fiducial markers. Target volume delineation was initially performed on the CT images and the corresponding FDG-PET data were subsequently used as an overlay to the CT data to define target volume. RESULTS: FDG-PET identified previously undetected distant metastatic disease in 8 patients making them ineligible for curative CRT (one patient presented some positive uptakes corresponding to concomitant pulmonary tuberculosis). Another patient was ineligible for curative treatment because fused CT/PET images demonstrated excessively extensive intrathoracic disease. The gross tumor volume (GTV) was decreased by CT/PET image fusion in 21 patients (23%) and was increased in 24 patients (26%). The GTV reduction was > or = 25% in 7 patients because CT/PET image fusion reduced pulmonary GTV in 6 patients (3 patients with atelectasis) and mediastinal nodal GTV in 1 patient. The GTV increase was > or = 25% in 14 patients due to an increase of the pulmonary GTV in 11 patients (4 patients with atelectasis) and detection of occult mediastinal lymph node involvement in 3 patients. Among 81 patients receiving a total dose > or = 60 Gy at ICRU point, after CT/PET image fusion, the percentage of total lung volume receiving more than 20 Gy (VL20) increased in 15 cases and decreased in 22 cases. The percentage of total heart volume receiving more than 36 Gy increased in 8 patients and decreased in 14 patients. The spinal cord volume receiving at least 45 Gy (2 patients) decreased. After multivariate analysis, one single independent factor made significant effect of FDG/PET on the modification of the size of the GTV: tumor with atelectasis (P = 0.0001). Conclusion. - Our study confirms that integrated hybrid PET/CT in the treatment position and coregistered images have an impact on treatment planning and management of patients with NSCLC. FDG images using dedicated PET scanners with modern image fusion techniques and respiration-gated acquisition protocols could improve CT/PET image coregistration. However, prospective studies with histological correlation are necessary and the impact on treatment outcome remains to be demonstrated.     

Positron emission tomography for target volume definition in the treatment of non-small cell lung cancer.

The additional benefit of positron emission tomography (PET) in the initial staging of non-small cell lung cancer (NSCLC) has generated interest in 18F-fluorodeoxyglucose (FDG) PET as a means of defining the extent of primary lung tumour for radiotherapy treatment planning (RTP). A review of published data suggests that PET results in a reduction in the CT-derived GTV for NSCLC primary target volume in 15% of the patients. This is principally due to the ability of PET to distinguish tumour from atelectasis. However, the difficulty of tumour edge definition, limited spatial resolution and tumour motion during image acquisition currently limits the accuracy of PET in target volume delineation in NSCLC without adjacent lung consolidation. This is compounded by the lack of data correlating PET with spatial pathology at the primary tumour site. With the current technical limitations, it is not established that PET can add accuracy to the CT-defined primary target delineation in RTP of NSCLC. It is hoped that advances in PET and combined PET/CT imaging may overcome some of the technical limitations. Future use of PET for primary tumour delineation in NSCLC will also be critically dependent on the detailed studies of imaging-pathology correlation.     

Observer variation in contouring gross tumor volume in patients with poorly defined non-small-cell lung tumors on CT: the impact of 18FDG-hybrid PET fusion.

PURPOSE: To quantify interobserver variation in gross tumor volume (GTV) localization using CT images for patients with non-small-cell lung carcinoma and poorly defined tumors on CT and to determine whether variability would be reduced if coregistered 2-[18F]fluoro-2-deoxy-d-glucose (FDG)-hybrid positron emission tomography (PET) with CT images were used. METHODS AND MATERIALS: Prospectively, 30 patients with non-small-cell lung carcinoma had CT and FDG-hybrid PET examinations in radiation treatment position on the same day. Images were coregistered using eight fiducial markers. Guidelines were established for contouring GTVs. Three radiation oncologists performed localization independently. The coefficient of variation was used to assess interobserver variability. RESULTS: The size of the GTV defined showed great variation among observers. The mean ratios of largest to smallest GTV were 2.31 and 1.56 for CT only and for CT/FDG coregistered data, respectively. The addition of PET reduced this ratio in 23 of 30 cases and increased it in 7. The mean coefficient of variation for GTV based on the combined modalities was significantly smaller (p < 0.01) than that for CT data only. CONCLUSIONS: High observer variability in CT-based definition of the GTV can occur. A more consistent definition of the GTV can often be obtained if coregistered FDG-hybrid PET images are used.     

Impact of computed tomography and F-deoxyglucose coincidence detection emission tomography image fusion for optimization of conformal radiotherapy in non–small-cell lung cancer

PURPOSE: To report a retrospective study concerning the impact of fused 18F-fluoro-deoxy-D-glucose (FDG)-hybrid positron emission tomography (PET) and CT images on three-dimensional conformal radiotherapy planning for patients with non-small-cell lung cancer. METHODS AND MATERIALS: A total of 101 patients consecutively treated for Stage I-III non-small-cell lung cancer were studied. Each patient underwent CT and FDG-hybrid PET for simulation treatment in the same treatment position. Images were coregistered using five fiducial markers. Target volume delineation was initially performed on the CT images, and the corresponding FDG-PET data were subsequently used as an overlay to the CT data to define the target volume. RESULTS: 18F-fluoro-deoxy-D-glucose-PET identified previously undetected distant metastatic disease in 8 patients, making them ineligible for curative conformal radiotherapy (1 patient presented with some positive uptake corresponding to concomitant pulmonary tuberculosis). Another patient was ineligible for curative treatment because the fused PET-CT images demonstrated excessively extensive intrathoracic disease. The gross tumor volume (GTV) was decreased by CT-PET image fusion in 21 patients (23%) and was increased in 24 patients (26%). The GTV reduction was > or = 25% in 7 patients because CT-PET image fusion reduced the pulmonary GTV in 6 patients (3 patients with atelectasis) and the mediastinal nodal GTV in 1 patient. The GTV increase was > or = 25% in 14 patients owing to an increase in the pulmonary GTV in 11 patients (4 patients with atelectasis) and detection of occult mediastinal lymph node involvement in 3 patients. Of 81 patients receiving a total dose of > or = 60 Gy at the International Commission on Radiation Units and Measurements point, after CT-PET image fusion, the percentage of total lung volume receiving >20 Gy increased in 15 cases and decreased in 22. The percentage of total heart volume receiving >36 Gy increased in 8 patients and decreased in 14. The spinal cord volume receiving at least 45 Gy (2 patients) decreased. Multivariate analysis showed that tumor with atelectasis was the single independent factor that resulted in a significant effect on the modification of the size of the GTV by FDG-PET: tumor with atelectasis (with vs. without atelectasis, p = 0.0001). CONCLUSION: The results of our study have confirmed that integrated hybrid PET/CT in the treatment position and coregistered images have an impact on treatment planning and management of non-small-cell lung cancer. However, FDG images using dedicated PET scanners and respiration-gated acquisition protocols could improve the PET-CT image coregistration. Furthermore, the impact on treatment outcome remains to be demonstrated.     

Feasibility of pathology-correlated lung imaging for accurate target definition of lung tumors

PURPOSE: To accurately define the gross tumor volume (GTV) and clinical target volume (GTV plus microscopic disease spread) for radiotherapy, the pretreatment imaging findings should be correlated with the histopathologic findings. In this pilot study, we investigated the feasibility of pathology-correlated imaging for lung tumors, taking into account lung deformations after surgery. METHODS AND MATERIALS: High-resolution multislice computed tomography (CT) and positron emission tomography (PET) scans were obtained for 5 patients who had non-small-cell lung cancer (NSCLC) before lobectomy. At the pathologic examination, the involved lung lobes were inflated with formalin, sectioned in parallel slices, and photographed, and microscopic sections were obtained. The GTVs were delineated for CT and autocontoured at the 42% PET level, and both were compared with the histopathologic volumes. The CT data were subsequently reformatted in the direction of the macroscopic sections, and the corresponding fiducial points in both images were compared. Hence, the lung deformations were determined to correct the distances of microscopic spread. RESULTS: In 4 of 5 patients, the GTV(CT) was, on average, 4 cm(3) ( approximately 53%) too large. In contrast, for 1 patient (with lymphangitis carcinomatosa), the GTV(CT) was 16 cm(3) ( approximately 40%) too small. The GTV(PET) was too small for the same patient. Regarding deformations, the volume of the well-inflated lung lobes on pathologic examination was still, on average, only 50% of the lobe volume on CT. Consequently, the observed average maximal distance of microscopic spread (5 mm) might, in vivo, be as large as 9 mm. CONCLUSIONS: Our results have shown that pathology-correlated lung imaging is feasible and can be used to improve target definition. Ignoring deformations of the lung might result in underestimation of the microscopic spread.     

Impact of FDG-PET on radiation therapy volume delineation in non-small-cell lung cancer

PURPOSE: Locoregional failure remains a significant problem for patients receiving definitive radiation therapy alone or combined with chemotherapy for non-small-cell lung cancer (NSCLC). Positron emission tomography (PET) with [(18)F]fluoro-2-deoxy-d-glucose (FDG) has proven to be a valuable diagnostic and staging tool for NSCLC. This prospective study was performed to determine the impact of treatment simulation with FDG-PET and CT on radiation therapy target volume definition and toxicity profiles by comparison to simulation with computed tomography (CT) scanning alone. METHODS: Twenty-six patients with Stages I-III NSCLC were studied. Each patient underwent sequential CT and FDG-PET simulation on the same day. Immobilization devices used for both simulations included an alpha cradle, a flat tabletop, 6 external fiducial markers, and a laser positioning system. A radiation therapist participated in both simulations to reproduce the treatment setup. Both the CT and fused PET/CT image data sets were transferred to the radiation treatment planning workstation for contouring. Each FDG-PET study was reviewed with the interpreting nuclear radiologist before tumor volumes were contoured. The fused PET/CT images were used to develop the three-dimensional conformal radiation therapy (3DCRT) plan. A second physician, blinded to the results of PET, contoured the gross tumor volumes (GTV) and planning target volumes (PTV) from the CT data sets, and these volumes were used to generate mock 3DCRT plans. The PTV was defined by a 10-mm margin around the GTV. The two 3DCRT plans for each patient were compared with respect to the GTV, PTV, mean lung dose, volume of normal lung receiving > or =20 Gy (V20), and mean esophageal dose. RESULTS: The FDG-PET findings altered the AJCC TNM stage in 8 of 26 (31%) patients; 2 patients were diagnosed with metastatic disease based on FDG-PET and received palliative radiation therapy. Of the 24 patients who were planned with 3DCRT, PET clearly altered the radiation therapy volume in 14 (58%), as follows. PET helped to distinguish tumor from atelectasis in all 3 patients with atelectasis. Unsuspected nodal disease was detected by PET in 10 patients, and 1 patient had a separate tumor focus detected within the same lobe of the lung. Increases in the target volumes led to increases in the mean lung dose, V20, and mean esophageal dose. Decreases in the target volumes in the patients with atelectasis led to decreases in these normal-tissue toxicity parameters. CONCLUSIONS: Radiation targeting with fused FDG-PET and CT images resulted in alterations in radiation therapy planning in over 50% of patients by comparison with CT targeting. The increasing availability of integrated PET/CT units will facilitate the use of this technology for radiation treatment planning. A confirmatory multicenter, cooperative group trial is planned within the Radiation Therapy Oncology Group.