Positron emission tomography in evaluating the response to treatment of brain tumors, lymphomas and breast cancer

Positron emission tomography (PET) with the glucose analogue (18)F-FDG is increasingly used to monitor tumour response in patients undergoing chemotherapy, radiotherapy or new therapeutic schemes including antiangiogenesis and molecular targeted cancer treatment. PET as a functional imaging technology provides timely, quantitative, cross-sectional, non invasive assessment of several biologic processes targeted by the above-mentioned therapies. Tests by the camera PET can be useful in distinguishing between radiation necrosis or scarring and tumour recurrence, thus evaluating response to therapy. The information provided by this technique is more sensitive and specific than that provided by conventional anatomic imaging modalities such as computerised tomography, magnetic resonance imaging or ultrasound and superior in evaluating the effectiveness of various treatment regimens early during therapy or after the completion of therapy. With this information in hand, physicians can modify ineffective therapy and consequently improve patient's outcome and reduce the cost of treatment. In the present review article we discuss the contribution of tests performed by the PET camera, mainly using (18)F-FDG as a radiotracer, in the evaluation of treatment response in patients with brain tumours, lymphomas and breast cancer.     

The role of 18F-FDG PET in staging and early prediction of response to therapy of recurrent gastrointestinal stromal tumors.

Gastrointestinal stromal tumors (GISTs) are gaining the interest of researchers because of impressive metabolic response to the targeted molecular therapeutic drug imatinib mesylate. Initial reports suggest an impressive role for (18)F-FDG PET in follow-up of therapy for these tumors. However, the role of (18)F-FDG PET versus that of CT has not been established. Therefore, we compared the roles of (18)F-FDG PET and CT in staging and evaluation of early response to imatinib mesylate therapy in recurrent or metastatic GIST. METHODS: The study included 54 patients who underwent (18)F-FDG PET and CT scans within 3 wk before initiation of imatinib mesylate therapy. Forty-nine of these patients underwent repeat scans 2 mo after therapy. The numbers of sites or organs containing lesions on (18)F-FDG PET and CT scans were compared. Corresponding lesions on (18)F-FDG PET and CT scans or those confirmed to be malignant in appearance by other imaging modalities or on follow-up were considered true positives. Lesions seen on (18)F-FDG PET or CT scans but not seen or confirmed to be of benign appearance with other imaging modalities or on follow-up were considered false positives. Measurements of the maximum standard uptake value (SUV) on (18)F-FDG PET scans and tumor size on CT scans were used for quantitative evaluation of early tumor response to therapy. RESULTS: A total of 122 and 114 sites and/or organs were involved on pretherapy (18)F-FDG PET and CT scans, respectively. The sensitivity and positive predictive values (PPVs) for CT were 93% and 100%; whereas these values for (18)F-FDG PET were 86% and 98%. However, the differences between these values for CT and (18)F-FDG PET were not statistically significant (P = 0.27 for sensitivity and 0.25 for PPV). This suggests comparable performance of (18)F-FDG PET and CT in staging GISTs. Repeat scans at 2 mo after therapy showed agreement between (18)F-FDG PET and CT scans in 71.4% of patients (57.1% having a good response to therapy and 14.3% lacking a response). Discrepant results between (18)F-FDG PET and CT were recorded for 28.6% of the patients. (18)F-FDG PET predicted response to therapy earlier than did CT in 22.5% of patients during a longer follow-up interval (4-16 mo), whereas CT predicted lack of response to therapy earlier than (18)F-FDG PET in 4.1%. One patient did not undergo long-term follow-up. These findings suggest that (18)F-FDG PET is superior to CT in predicting early response to therapy in recurrent or metastatic GIST patients. CONCLUSION: The performances of (18)F-FDG PET and CT are comparable in staging GISTs before initiation of imatinib mesylate therapy. However, (18)F-FDG PET is superior to CT in predicting early response to therapy. Thus, (18)F-FDG PET is a better guide for imatinib mesylate therapy.     

18F-FDG PET显像在乳腺癌中的应用

^18F-FDG(^18F-氟脱氧葡萄糖)PET(正电子发射型计算断层显像)是反映恶性肿瘤代谢特征的一种无创性的功能显像方法。在绝大多数肿瘤中均得到广泛应用。本文通过对国内外乳腺癌^18F-FDG PET。显像的文章进行全面综合分析，旨在探讨^18F-FDG PET显像在乳腺癌中的应用原理及其临床应用价值。与传统影像学相比，^18F-FDG PET。显像能够更为准确地发现原发性乳腺癌远处转移和局部复发，可以在治疗早期及时评价化疗疗效以指导临床治疗。对于原发性乳腺癌的诊断。PET显像不作为首选检查。但对于临床检查或常规影像检查难以进行或无明确结论的病人。PET显像可以作为其乳腺肿块定性诊断的最佳选择。     

PET in the assessment of therapy response in patients with carcinoma of the head and neck and of the esophagus.

In patients with carcinoma of the head and neck and of the esophagus, metabolic and functional imaging by PET with (18)F-FDG has a pivotal role in the evaluation of tumor response to therapy, specifically, in the prediction of progression-free survival and overall survival. Metabolic imaging allows the detection of biochemical changes within tumor cells as opposed to identifiable morphologic changes. Anatomic imaging modalities do not reliably differentiate between responders and nonresponders early during the course of follow-up. The correlation between histopathologic tumor response after preoperative therapy and clinical prognosis is well established for many cancers. Squamous carcinoma of the head and neck and esophageal carcinoma demonstrate avid (18)F-FDG uptake. For these cancers, (18)F-FDG PET parallels histopathologic findings in its ability to detect residual viable tumor; therefore, it is a valuable tool for the noninvasive assessment of histopathologic tumor response in advanced-stage cases after neoadjuvant therapy before surgery. Early determination of nonresponders is of prime importance, as timely therapy modification can be accomplished for patients who do not demonstrate a response to therapy. This determination is exceptionally important for head and neck and esophageal malignancies, both of which are known for their unfavorable prognosis, as early modifications in therapy regimens for nonresponders may improve patient outcome. There is now evidence that (18)F-FDG PET is a sensitive and specific method for determining therapy response and for providing important prognostic information for these cancers. Therefore, (18)F-FDG PET may change patient management and lead to improved survival for a selected group of patients with carcinoma of the head and neck and of the esophagus.     

18F-FDG PET在淋巴瘤分期和治疗反应评价中的价值

18F-FDG PET显像对淋巴瘤的诊断、分期作用显著,对淋巴瘤病灶的探测灵敏度和准确性高于67Ga显像.在化疗过程中和化疗后持续18F-FDG PET阳性对预测复发有高灵敏度.治疗结束时18F-FDG PET阴性提示患者预后好.与其他常规显像相比,18F-FDG PET在监测淋巴瘤疗效、判断治疗反应方面有独特优势.     

颅内肿瘤放射治疗后18F-氟代脱氧葡萄糖PET的临床意义

放射治疗是颅内良恶性肿瘤安全有效的治疗方法,18F—FDG PET可以提供肿瘤细胞生物特性信息,能区分颅内肿瘤放射治疗后射线损伤与肿瘤复发,灵敏度为80%-90％,特异度为 40%～100％;能预测3～4级复发恶性胶质瘤放射治疗的生存时间,预测颅内肿瘤放射治疗预后和评价治疗反应;结合其他影像方法可提高颅内肿瘤放射治疗诊断准确性。     

Dynamic imaging of transient metabolic processes by small-animal PET for the evaluation of photosensitizers in photodynamic therapy of cancer.

This study evaluated the potential use of dynamic PET to monitor transient metabolic processes and to investigate the mechanisms of action of new photosensitizing drugs in the photodynamic therapy (PDT) of cancer. METHODS: Rats bearing 2 mammary tumors received different phthalocyanine-based photosensitizers. The following day, the animals were positioned in a Sherbrooke small-animal PET scanner and continuously infused with 18F-FDG while dynamic images were acquired for 2 h. During that period, one of the 2 tumors was exposed for 30 min to red light delivered by a small diode laser to activate PDT. RESULTS: 18F-FDG time-activity curves during PDT showed distinct transient patterns characterized by a drop and subsequent recovery of tumor 18F-FDG uptake rates. Variations in these rates and response delay parameters revealed tumoral and systemic metabolic processes that correlated with differences in mechanism of action between drugs, that is, direct tumor cell kill or initial vascular shutdown. CONCLUSION: Real-time follow-up of tumor response to PDT as monitored by dynamic 18F-FDG PET has been shown to correlate with the mechanisms of action of photosensitizing drugs in vivo. This new imaging paradigm can be exploited to monitor a variety of transient cellular and molecular processes as they occur in vivo, enabling the mechanisms of action of therapeutic interventions to be scrutinized and their efficacy predicted in real time.     

Impact of whole-body 18F-FDG PET on staging and managing patients for radiation therapy.

Whole-body PET with (18)F-FDG has proven to be a very effective imaging modality for staging of malignant tumors. This study was performed to evaluate the impact of (18)F-FDG PET on staging and managing patients for radiation therapy. METHODS: The treatment records of 202 consecutive patients (98 male, 104 female; mean age, 56.9 y; age range, 8-91 y) with different malignant tumors were reviewed. Radiation therapy was intended for all patients. The diagnoses were head and neck tumors (n = 55), gynecologic tumors (n = 28), breast cancer (n = 28), lung cancer (n = 26), malignant lymphomas (n = 24), tumors of the gastrointestinal tract (n = 18), and others (n = 23). Whole-body PET was performed before radiation therapy. The alteration of PET on each patient's staging and management decisions for radiation therapy were determined. RESULTS: For 55 of 202 patients (27%), PET results changed the patients' management in radiation therapy. In 18 cases (9%), PET resulted in a cancellation of radiation therapy because of the detection of previously unknown distant metastases (8 patients), additional lymph node metastases (9 patients), residual tumor (6 patients), or the exclusion of active disease (2 patients). In 6 patients, >1 incremental reason was found for cancellation. In 21 PET examinations (10%), PET results changed the intention of radiation treatment (curative or palliative). The radiation dose was changed in 25 cases (12%). A change of radiation volume was necessary in 12 patients (6%). CONCLUSION: The results of this study show that (18)F-FDG PET has a major impact on the management of patients for radiation therapy, influencing both the stage and the management in 27% of patients.     

18F-FDG PET of patients with Hürthle cell carcinoma.

Hürthle cell carcinoma is an uncommon differentiated thyroid cancer characterized by an aggressive clinical course and low avidity for (131)I. Treatment usually involves an aggressive surgical approach often combined with (131)I. (18)F-FDG PET has been helpful in the staging and evaluation of many types of aggressive malignancy. No reports to date have described the utility of PET in a series of patients with Hürthle cell cancer. We reviewed our experience with (18)F-FDG PET in the care of patients with Hürthle cell carcinoma to determine the likelihood of uptake in these cancers and the effect of (18)F-FDG PET on patient care. METHODS: Patients with Hürthle cell cancer who were seen between June 2000 and April 2002 and were imaged with (18)F-FDG PET were included. Imaging and clinical data were reviewed. PET results were compared with the results of anatomic imaging (CT, sonography, or MRI) and (131)I imaging when performed. Patient charts were reviewed to identify any change in management that resulted from the (18)F-FDG PET findings. RESULTS: Fourteen (18)F-FDG PET scans of 12 patients were obtained in the time frame indicated. All patients had documented Hürthle cell carcinoma. PET showed intense (18)F-FDG uptake in all known Hürthle cell cancer lesions but one. PET showed disease not identified by other imaging methods in 7 of the 14 PET scans. PET identified distant metastatic disease (5) or local disease (2) that was more extensive than otherwise demonstrated. In 7 of the 14 scans, the information provided by PET was used to guide or change therapy. CONCLUSION: Hürthle cell carcinoma demonstrates intense uptake on (18)F-FDG PET images. PET improves disease detection and disease management in patients with Hürthle cell carcinoma relative to anatomic or iodine imaging. (18)F-FDG PET should be recommended for the evaluation and clinical management of patients with Hürthle cell carcinoma.     

18F-FDG PET/CT在儿童及青少年淋巴瘤诊治中的应用价值

儿童及青少年淋巴瘤占所有儿科恶性肿瘤的10%~15%,其多为高度侵袭性肿瘤,较成人更易侵犯结外组织。准确的分期以及早期疗效评价对儿童及青少年淋巴瘤患者具有重要价值。传统影像学方法（超声、CT、MRI及67Ga成像）在其诊治过程中存在一定的局限性,18F-FDG PET/CT是将PET的功能代谢显像与CT的解剖结构显像相融合的一种新型成像技术。笔者通过对18F-FDG PET/CT检查在儿童及青少年淋巴瘤中的分期、疗效评级、随访中的作用作一综述,发现18F-FDG PET/CT在淋巴结、脾脏监测方面具有更高的灵敏度,可通过一次显像发现更多的病灶,在分期方面的准确性优于传统影像学方法。同时,因其代谢改变早于解剖形态的改变,能更早期、准确地评估疗效,对残留病灶的性质进行判断。由于其较低的复发率,需权衡在随访过程中监测复发及辐射暴露之间的利弊关系。     

肿瘤增殖显像剂3'-脱氧-3'-18F-氟代胸苷

18F-氟代脱氧葡萄糖(18F-FDG)是广泛用于肿瘤诊断的PET显像剂,由于所有细胞都利用葡萄糖,因此,18F-FDG不是特异的肿瘤显像剂.3'-脱氧-3'-18F-氟代胸苷(18F-FLT)克服了18F-FDG的局限性,并可以进行细胞增殖显像.对于肿瘤的PET研究,18F-FLT是理想的反映增殖特性的示踪剂,18F-FLT利用胸苷激酶催化的磷酸化作用来评价DNA复制过程,可以准确地评估肿瘤细胞DNA的合成和细胞增殖活性,可用于肿瘤的早期诊断及鉴别诊断、化疗和放疗的疗效监测,是很有希望和发展前途的PET显像剂.     

PET代谢显像剂11C-乙酸盐在临床中的应用

^18F-氟脱氧葡萄糖（^18F-FDG）是一种最常用的肿瘤正电子显像剂,但对于炎性病变鉴别困难,易得出肿瘤假阳性诊断结果。PET代谢显像剂^11C-乙酸能够弥补。^18F-FDGPET的某些不足,已用于各类肿瘤的诊断及鉴别诊断,特别是在肝癌以及前列腺癌等的诊断及鉴别诊断方面明显优于^18F-FDGPET;基于^11C-乙酸盐的特性,也常被用于心肌血流和灌注显像。     

FDG PET对肿瘤的评估价值

正电子发射体层(PET)是一种能够识别肿瘤内生化、生理变化的诊断影像技术，FDGPET可明显提高肿瘤诊断的准确性。肿瘤的FDG摄入量是与其内对葡萄糖需求量增加的有增殖能力的肿瘤细胞的代谢率呈正比的。FDG PET在肿瘤应用方面，对肿瘤的分期、分型，复发、转移的早期诊断，坏死与存活组织的鉴别，肿瘤生物特征的预测，及治疗反应的监测作用都得到了广泛承认。     

11C-胆碱与18F-FDG双时相PET显像在孤立性肺结节鉴别诊断中的应用

目的 比较^11C-胆碱、18F-脱氧葡萄糖（FDG）和^18F-FDG双时相PET显像对鉴别肺部孤立性结节良恶性的价值。方法16例临床疑为肺肿瘤的患者进行^18F-FDGPET显像（注药后1h显像，2h后行延迟显像）、^11C-胆碱PET显像（3d内，于注药后10min进行）。图像判断以标准摄取值（SUV）作为半定量指标，异常放射性浓聚灶以SUV〉2．5为葡萄糖代谢增高，^18F-FDG延迟显像SUV上升≥10％为恶性病变（阳性），如下降或升高〈10％为良性病变（阴性）；^11C-胆碱异常摄取灶以SUV〉2．0为阳性。所有病例进行随访，以显像诊断是否符合病理检查结果作为判断标准。结果病理检查结果证实12例肺癌，3例结核，1例结节病。^11C-胆碱PET显像确诊了12例肿瘤中的ll例，而^18F-FDG PET显像确诊10例（10／12例），双时相^18F-FDG PET显像确诊11例。4例良性病变者，^11C-胆碱PET显像能较好鉴别；而^18F-FDG PET显像2例假阳性，结合延迟显像仅1例假阳性。结论 ^11C-胆碱和^18F-FDG PET显像均能较好地鉴别肺部良恶性肿瘤。但^11C-胆碱和双时相^18F-FDGPET显像优于常规^18F-FDGPET显像，三者联合能提高对肺部病变的诊断效率。     

Prospective comparison of 18F-FDG PET with conventional imaging modalities (MRI, CT, and 67Ga scintigraphy) in assessment of combined intraarterial chemotherapy and radiotherapy for head and neck carcinoma.

To preserve the oral organs and functions in patients with head and neck carcinoma, accurate determination of the appropriate treatment after neoadjuvant chemotherapy and radiotherapy is of critical importance. We evaluated the diagnostic accuracy of (18)F-FDG PET relative to that of other conventional imaging modalities in the assessment of therapeutic response after combined intraarterial chemotherapy and radiotherapy as an organ preservation protocol. METHODS: The study was prospectively performed on 23 consecutive patients with head and neck squamous cell carcinoma who completed the treatment regimen and underwent 2 (18)F-FDG PET studies before and after neoadjuvant chemoradiotherapy. (67)Ga scintigraphy (only before therapy) as well as MRI and CT (both before and after therapy) were also performed. All images were blindly and independently interpreted without knowledge of histologic findings. The level of confidence in image interpretation was graded by means of a 5-point rating system (0 = definitely no tumor to 4 = definite tumor). RESULTS: Before treatment, (18)F-FDG PET detected primary tumors in all 23 patients and was more sensitive (100%) than MRI (18/23; 78.3%), CT (15/22; 68.2%), and (67)Ga scintigraphy (8/20; 40%), with a confidence level of 3 or 4 as a positive tumor finding. After chemoradiotherapy, residual tumors were histologically confirmed in 4 patients (pathologic complete response rate, 19/23; 82.6%). Although posttreatment (18)F-FDG PET showed almost equal sensitivity (4/4; 100%) compared with MRI (3/3; 100%) or CT (3/4; 75%), its specificity (17/19; 89.5%) was superior to MRI (7/17, 41.2%) and to CT (10/17; 58.8%) for primary lesions. Regarding metastases to neck lymph nodes, only specificity for posttreatment images was calculated because no metastasis was confirmed in any patients after treatment. Six subjects had (18)F-FDG PET-positive lymph nodes, which had pathologically no tumor cells and suggested an inflammatory reactive change after therapy. Therefore, the specificity of posttreatment (18)F-FDG PET (17/23; 73.9%) was almost identical to that of MRI (17/20; 85%) and CT (16/21; 76.2%) for neck metastasis. With combined chemoradiotherapy monitored with (18)F-FDG PET, 8 patients avoided surgery and the remaining 15 patients underwent a reduced form of surgery. CONCLUSION: (18)F-FDG PET facilitates differentiation of residual tumors from treatment-related changes after chemoradiotherapy, which may be occasionally difficult to characterize by anatomic images. (18)F-FDG PET has a clinical impact for the management of patients with head and neck cancers after neoadjuvant chemoradiotherapy by optimizing surgical treatment for each patient and contributes to the improvement of the patient's quality of life.     

Role of positron emission tomography/computed tomography in adrenal and neuroendocrine tumors: fluorodeoxyglucose and nonfluorodeoxyglucose tracers

Positron emission tomography (PET) has seen an increasing clinical utilization in the last decade, such that it is now a standard oncology imaging modality. Its success is based on the detection of altered fluorine-18 fluorodeoxyglucose (18F-FDG) biodistribution, reflecting glucose transport/metabolism in malignant tumor tissues. Integrated PET/computed tomography cameras combine functional and anatomical information in a synergistic manner that improves diagnostic interpretation, and newer positron-emitting radiopharmaceuticals have been developed to expand the application of non-FDG PET imaging. The increasing use of cross-sectional imaging procedures has led to a more frequent detection of incidental adrenal masses. Although conventional imaging modalities such as computed tomography and MRI can characterize the majority of these lesions, 18F-FDG PET has been reported as a useful tool to distinguish benign from malignant etiologies in indeterminate adrenal masses. Although 18F-FDG PET has enjoyed success in staging a wide range of cancers, including detection of adrenal metastases and evaluation of adrenocortical carcinoma, it has had limited impact for the evaluation of neuroendocrine tumors. Positron-emitting amine precursor and somatostatin analogs have been validated in research settings to provide accurate imaging of enterochromaffin and chromaffin neuroendocrine tumors and medullary thyroid cancer. The aim of this review article is to provide an overview of the role of 18F-FDG and newer positron-emitting radiopharmaceuticals in the evaluation of adrenal and neuroendocrine tumors.     

18F-氟脱氧葡萄糖PET及PET-CT在食管癌中的应用价值

食管癌的预后较差,切除术的致死率和致残率较高,术前正确分期对确定治疗方案尤为重要。PET是对CT、MRI、食管镜等常规检查的有益补充。受分辨率的影响,PET较难确定肿瘤的浸润程度,但对远处转移灶的诊断明显优于CT、MRI等常规检查,诊断复发性食管癌准确率较高,能有效鉴别手术瘢痕和复发,有效评价放疗、化疗的疗效。结合传统影像学检查,18F-氟脱氧葡萄糖PET及PET-CT能较为准确地进行术前分期,纠正不正确的治疗方案,改善食管癌患者的预后。     

Use of PET for monitoring cancer therapy and for predicting outcome.

PET with the glucose analog (18)F-FDG is increasingly used to monitor tumor response in patients undergoing chemotherapy and chemoradiotherapy. Numerous studies have shown that (18)F-FDG PET is an accurate test for differentiating residual viable tumor tissue from therapy-induced fibrosis. Furthermore, quantitative assessment of therapy-induced changes in tumor (18)F-FDG uptake may allow the prediction of tumor response and patient outcome very early in the course of therapy. Treatment may be adjusted according to the chemosensitivity and radiosensitivity of the tumor tissue in an individual patient. Thus, (18)F-FDG PET has an enormous potential to reduce the side effects and costs of ineffective therapy. This review focuses on the practical aspects of (18)F-FDG PET for treatment monitoring and on how to perform a quantitative assessment of tumor (18)F-FDG uptake in clinical studies.     

Molecular imaging with 123I-FIAU, 18F-FUdR, 18F-FET, and 18F-FDG for monitoring herpes simplex virus type 1 thymidine kinase and ganciclovir prodrug activation gene therapy of cancer.

The ability to monitor tumor responses during prodrug activation gene therapy and other anticancer gene therapies is critical for their translation into clinical practice. Previously, we demonstrated the feasibility of noninvasive in vivo imaging with 131I-5-iodo-2'-fluoro-1-beta-D-arabinofuranosyluracil (131I-FIAU) for monitoring herpes simplex virus type 1 thymidine kinase (HSV1-tk) cancer gene expression in an experimental animal model. Here we tested the efficacy of SPECT with 123I-FIAU and PET with 5-18F-fluoro-2'-deoxyuridine (18F-FUdR), 2-18F-fluoroethyl-L-tyrosine (18F-FET), and 18F-FDG for monitoring tumor responses during prodrug activation gene therapy with HSV1-tk and ganciclovir (GCV). METHODS: In the flanks of FVB/N female mice, 4 tumors per animal were established by subcutaneous injection of 1 x 10(5) cells of NG4TL4 sarcoma cells, HSV1-tk-transduced NG4TL4-STK cells, or a mixture of these cells in different proportions to model different efficacies of transfection and HSV1-tk gene expression levels in tumors. Ten days later, the animals were treated with GCV (10 mg/kg/d intraperitoneally) for 7 d. Gamma-Imaging with 123I-FIAU and PET with 18F-FUdR, 18F-FET, and 18F-FDG were performed before and after initiation of therapy with GCV in the same animal. RESULTS: Before GCV treatment, no significant difference in weight and size was found in tumors that expressed different HSV1-tk levels, suggesting similar in vivo proliferation rates for NG4TL4 and NG4TL4-STK sarcomas. The accumulation of 123I-FIAU at 24 h after injection was directly proportional to the percentage of NG4TL4-STK cells in the tumors. The 123I-FIAU accumulation at 4 and 7 d of GCV therapy decreased significantly compared with pretreatment levels and was proportional to the percentage of HSV1-tk-positive tumor cells. Tumor uptake of 18F-FUdR in all HSV1-tk-expressing tumors also decreased significantly compared with pretreatment levels and was proportional to the percentage of HSV1-tk-positive tumor cells. The accumulation of 18F-FET decreased minimally (about 1.5-fold) and 18F-FDG decreased only 2-fold after 7 d of GCV therapy, and the degree of reduction was proportional to the percentage of HSV1-tk-positive tumor cells. CONCLUSION: We have shown that gamma-camera imaging with 123I-FIAU was the most reliable method for prediction of tumor response to GCV therapy, which was proportional to the magnitude of HSV1-tk expression in tumor tissue. 123I-FIAU imaging can be used to verify the efficacy of elimination of HSV1-tk-expressing cells by therapy with GCV. PET with 18F-FUdR reliably visualizes proliferating tumor tissue and is most suitable for the assessment of responses in tumors undergoing HSV1-tk plus GCV prodrug activation gene therapy. PET with 18F-FDG or 18F-FET can be used as additional "surrogate" biomarkers of the treatment response, although these radiotracers are less sensitive than 18F-FUdR for monitoring tumor responses to prodrug activation gene therapy with HSV1-tk and GCV in this sarcoma model.     

Utility of 18F-FDG PET in evaluating cancers of lung

PET has seen rapid progression in recent years, with applications in oncology leading the way. The glucose analog (18)F-FDG is the most commonly used PET radiopharmaceutical and has been shown to accumulate avidly in several different neoplasms, including cancers of the lung. The following discussion will review the physiologic basis for the uptake of (18)F-FDG in lung neoplasms and demonstrate the utility of (18)F-FDG PET in lung cancer. A brief review of other PET radiopharmaceuticals in lung cancer imaging, and dual-modality PET/CT scanners, will be presented. Upon completion of this article, the reader should be able to describe the pharmacokinetics of (18)F-FDG and discuss the efficacy of (18)F-FDG PET scans in the evaluation of solitary pulmonary nodules, disease staging, and monitoring response to therapy. Additionally, the reader should be able to compare (18)F-FDG PET with conventional anatomic imaging and describe some of the technical challenges of PET/CT fusion imaging.