Recommendations on the Use of 18F-FDG PET in Oncology

Comparison of diagnostic and prognostic capabilities of ¹⁸F-FDG-PET/CT, ¹³¹I-scintigraphy, and diffusion-weighted magnetic resonance imaging for postoperative thyroid cancer

PURPOSE

The first aim of this study was to compare the detectability of metastasis of postoperative differentiated thyroid cancer (DTC) among (131)I whole body scintigraphy (IWBS), fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT), and diffusion-weighted magnetic resonance imaging (DWI). The second aim was to clarify the association between the image pattern and prognosis.

MATERIALS AND METHODS

We evaluated 70 postoperative DTC patients on both a patient basis and an organ basis (lymph nodes, lung, bone), and we analyzed the correlation between the image pattern and the prognosis.

RESULTS

For the patient-basis analysis, the detectability by IWBS, PET/CT, and DWI was 67.1%, 84.2%, and 57.6%, respectively. IWBS provided complementary information to that provided by PET/CT in 11 of 70 (15.7%) cases. For the organ-basis analysis, IWBS was the best detector for lymph node metastasis (72.4%). PET/CT was superior to IWBS for detecting metastasis of bone (85.7% vs. 71.4%) and lung (94.1% vs. 62.7%). For the correlation analysis, PET and DWI positivity were the factors predicting a poor prognosis.

CONCLUSION

PET/CT was the best modality for detecting metastases in postoperative DTC patients, although IWBS provided complementary information. Because PET/CT and DWI gave similar information (e.g., positivity) suggesting poor prognoses, the combination of IWBS and DWI might be the method of choice for monitoring postoperative DTC.

Dual-isotope PET using positron-gamma emitters

Positron emission tomography (PET) is widely recognized as a highly effective functional imaging modality. Unfortunately, standard PET cannot be used for dual-isotope imaging (which would allow for simultaneous investigation of two different biological processes), because positron-electron annihilation products from different tracers are indistinguishable in terms of energy. Methods that have been proposed for dual-isotope PET rely on differences in half-lives of the participating isotopes; these approaches, however, require making assumptions concerning kinetic behavior of the tracers and may not lead to optimal results. In this paper we propose a novel approach for dual-isotope PET and investigate its performance using GATE simulations. Our method requires one of the two radioactive isotopes to be a pure positron emitter and the second isotope to emit an additional high-energy gamma in a cascade simultaneously with positron emission. Detection of this auxiliary prompt gamma in coincidence with the annihilation event allows us to identify the corresponding 511 keV photon pair as originating from the same isotope. Two list-mode datasets are created: a primary dataset that contains all detected 511 keV photon pairs from both isotopes, and a second, tagged (much smaller) dataset that contains only those PET events for which a coincident prompt gamma has also been detected. An image reconstructed from the tagged dataset reflects the distribution of the second positron-gamma radiotracer and serves as a prior for the reconstruction of the primary dataset. Our preliminary simulation study with partially overlapping (18)F/(22)Na and (18)F/(60)Cu radiotracer distributions showed that in these two cases the dual-isotope PET method allowed for separation of the two activity distributions and recovered total activities with relative errors of about 5%.

On the significance of defective block detectors in clinical (18)F-FDG PET/CT imaging

INTRODUCTION

Clinical positron emission tomography (PET) systems based on block detector designs suffer occasional block detector failures, which can result in patient scan cancelations. In this study, we examine the effect of defective block detectors on measurements of maximum standard uptake value (SUV(max)) and clinical image quality in 3D 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) PET/computed tomography (CT) imaging.

METHODS

A Data Spectrum anthropomorphic torso phantom (4.7 kBq/ml FDG concentration, defined as SUV of 1.0) was imaged in a normally functioning Siemens Biograph 16 HiRez PET/CT scanner using a whole-body imaging protocol. Spherical lesions with SUVs ranging from 10.0 to 13.5 were placed in the phantom. Defective block detectors were simulated by zeroing the appropriate lines of response in the sinograms. Eleven one-block and seventeen two-block defect configurations were simulated in the phantom sinograms. The images were reconstructed, and the measured SUV(max) was compared with the SUV(max) for the images without detector defects. Twelve clinical PET scans were evaluated before and after simulated detector defects cases ranging from a single block up to 12 blocks (bucket). The reconstructed images were independently scored for image quality and clinical diagnosis by two nuclear physicians blinded to the presence and severity of defects in the images.

RESULTS

The mean change in phantom SUV(max) was -2% (range, -6% to +3%) in the presence of a single defective block detector and -3% (range, -11% to +7%) in the presence of two defective block detectors, respectively. For the clinical patient studies, there was no significant decline in image quality score from one to two defective block detectors. In the case of 3-4 defective block detectors, image quality became marginal, and image degradation was significant with a defective bucket (12 blocks).

CONCLUSION

For one or two defective block detectors in a 3D PET camera, while waiting for the repair service, routine patient scans can proceed with the proviso that the reading physician is made aware of the detector failure.

Akt-dependent glucose metabolism promotes Mcl-1 synthesis to maintain cell survival and resistance to Bcl-2 inhibition

Most cancer cells utilize aerobic glycolysis, and activation of the phosphoinositide 3-kinase/Akt/mTOR pathway can promote this metabolic program to render cells glucose dependent. Although manipulation of glucose metabolism may provide a means to specifically eliminate cancer cells, mechanistic links between cell metabolism and apoptosis remain poorly understood. Here, we examined the role and metabolic regulation of the antiapoptotic Bcl-2 family protein Mcl-1 in cell death upon inhibition of Akt-induced aerobic glycolysis. In the presence of adequate glucose, activated Akt prevented the loss of Mcl-1 expression and protected cells from growth factor deprivation-induced apoptosis. Mcl-1 associated with and inhibited the proapoptotic Bcl-2 family protein Bim, contributing to cell survival. However, suppression of glucose metabolism led to induction of Bim, decreased expression of Mcl-1, and apoptosis. The proapoptotic Bcl-2/Bcl-xL/Bcl-w inhibitor, ABT-737, shows clinical promise, but Mcl-1 upregulation can promote resistance. Importantly, inhibition of glucose metabolism or mTORC1 overcame Mcl-1-mediated resistance in diffuse large B cell leukemic cells. Together these data show that Mcl-1 protein synthesis is tightly controlled by metabolism and that manipulation of glucose metabolism may provide a mechanism to suppress Mcl-1 expression and sensitize cancer cells to apoptosis.

18F-fluorodeoxy-glucose positron emission tomography marks MYC-overexpressing human basal-like breast cancers

In contrast to normal cells, cancer cells avidly take up glucose and metabolize it to lactate even when oxygen is abundant, a phenomenon referred to as the Warburg effect. This fundamental alteration in glucose metabolism in cancer cells enables their specific detection by positron emission tomography (PET) following i.v. injection of the glucose analogue (18)F-fluorodeoxy-glucose ((18)FDG). However, this useful imaging technique is limited by the fact that not all cancers avidly take up FDG. To identify molecular determinants of (18)FDG retention, we interrogated the transcriptomes of human-cancer cell lines and primary tumors for metabolic pathways associated with (18)FDG radiotracer uptake. From ninety-five metabolic pathways that were interrogated, the glycolysis, and several glycolysis-related pathways (pentose phosphate, carbon fixation, aminoacyl-tRNA biosynthesis, one-carbon-pool by folate) showed the greatest transcriptional enrichment. This "FDG signature" predicted FDG uptake in breast cancer cell lines and overlapped with established gene expression signatures for the "basal-like" breast cancer subtype and MYC-induced tumorigenesis in mice. Human breast cancers with nuclear MYC staining and high RNA expression of MYC target genes showed high (18)FDG-PET uptake (P < 0.005). Presence of the FDG signature was similarly associated with MYC gene copy gain, increased MYC transcript levels, and elevated expression of metabolic MYC target genes in a human breast cancer genomic dataset. Together, our findings link clinical observations of glucose uptake with a pathologic and molecular subtype of human breast cancer. Furthermore, they suggest related approaches to derive molecular determinants of radiotracer retention for other PET-imaging probes.

Clinical relevance of incidental finding of focal uptakes in the colon during 18F-FDG PET/CT studies in oncology patients without known colorectal carcinoma and evaluation of the impact on management

AIMS

To assess the significance and the impact of focal FDG uptake in the colon in oncology patients without known colorectal carcinoma.

MATERIALS AND METHODS

A retrospective study was undertaken on 2,220 (18)F-FDG PET/CT studies carried out consecutively in the Nuclear Medicine Department in our hospital from 2 December 2008 to 31 May 2010. Inclusion criteria were patients with abnormal (18)F-FDG uptake in colorectal area that could not be explained (or not previously known) by their clinical histories. Patients previously diagnosed with colorectal carcinoma were excluded. A total of 86 patients (57 male, average age 63.4, range 46-85) were finally included. Colonoscopy with biopsy was established as a reference test. The impact of these findings on the diagnostic-therapeutic management in these patients was evaluated.

RESULTS

A colonoscopy was performed in 54 of the 86 patients, this examination not having been done up-to-date in the remaining 32 patients. Biopsy was obtained in 43 lesions of the 54 patient in whom a colonoscopy was performed. Colon disease was detected in 49 of these 54 patients, obtaining 54 FDG incidental foci which corresponded to 10 previously unsuspected primary colorectal carcinoma, 3 metastases, 27 adenomatous polyps with different degrees of dysplasia and 14 inflammatory processes. In the remaining 5 patients, the colonoscopy was normal. PET/CT modified the diagnostic and treatment management in most of the patients (49/54, that is 91%).

CONCLUSIONS

These results confirm the need to determine the cause of abnormal (18)F-FDG colorectal uptakes in the PET/CT studies by using colonoscopy and biopsy. This approach allows for the detection and early treatment of malignant and premalignant lesions.

Curative treatment of oesophageal carcinoma: current options and future developments

Since the 1980s major advances in surgery, radiotherapy and chemotherapy have established multimodal approaches as curative treatment options for oesophageal cancer. In addition the introduction of functional imaging modalities such as PET-CT created new opportunities for a more adequate patient selection and therapy response assessment.

The majority of oesophageal carcinomas are represented by two histologies: squamous cell carcinoma and adenocarcinoma. In recent years an epidemiological shift towards the latter was observed. From a surgical point of view, adenocarcinomas, which are usually located in the distal third of the oesophagus, may be treated with a transhiatal resection, whereas squamous cell carcinomas, which are typically found in the middle and the upper third, require a transthoracic approach. Since overall survival after surgery alone is poor, multimodality approaches have been developed. At least for patients with locally advanced tumors, surgery alone can no longer be advocated as routine treatment. Nowadays, scientific interest is focused on tumor response to induction radiochemotherapy. A neoadjuvant approach includes the early and accurate assessment of clinical response, optimally performed by repeated PET-CT imaging and endoscopic ultrasound, which may permit early adaption of the therapeutic concept. Patients with SCC that show clinical response by PET CT are considered to have a better prognosis, regardless of whether surgery will be performed or not. In non-responding patients salvage surgery improves survival, especially if complete resection is achieved.

Pulmonary aspergilloma mimicking metastasis from papillary thyroid cancer

BACKGROUND

Whole-body scans (WBSs) based on diagnostic or therapeutic doses of I-131 can visualize metastatic lesions in thyroid cancer patients who have undergone total thyroidectomy. However, a variety of unusual lesions may cause false-positive results, and therefore, careful evaluation of abnormal scans is imperative to avoid unnecessary surgical removal or high-dose radioiodine treatment. Here, we report a patient with pulmonary aspergilloma mimicking metastasis of thyroid cancer on WBS.

SUMMARY

A 53-year-old woman with papillary thyroid cancer stage III (T1N1aM0) who had undergone total thyroidectomy and 150 mCi of radioiodine treatment for remnant ablation was found to have focal intense radioiodine accumulation in the left lung field by WBS, suggestive of pulmonary metastasis, at 5 days after I-131 administration. Whole-body F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) and Tc-99m methoxyisobutyl isonitrile scans showed no remarkable tracer accumulation at the pulmonary nodule. An enhanced chest CT scan demonstrated a nonenhancing pulmonary nodule with an air-crescent sign suggestive of pulmonary fungus ball. A subsequent blood test for precipitating antibodies to Aspergillus antigens produced a result of 29.9 U/mL (reference range: 0-8 U/mL). The patient was clinically diagnosed as having pulmonary aspergilloma based on serologic test and radiologic imaging results.

CONCLUSION

Extreme caution should be exercised when interpreting abnormal radioiodine WBS findings when the serum thyroglobulin is normal and imaging characteristics indicate a benign condition. Pulmonary aspergilloma is a cause of a false-positive lesion when radioiodine WBSs are performed.

Single photon emission computed tomography/positron emission tomography imaging and targeted radionuclide therapy of melanoma: new multimodal fluorinated and iodinated radiotracers

This study reports a series of 14 new iodinated and fluorinated compounds offering both early imaging ((123)I, (124)I, (18)F) and systemic treatment ((131)I) of melanoma potentialities. The biodistribution of each (125)I-labeled tracer was evaluated in a model of melanoma B16F0-bearing mice, using in vivo serial γ scintigraphic imaging. Among this series, [(125)I]56 emerged as the most promising compound in terms of specific tumoral uptake and in vivo kinetic profile. To validate our multimodality concept, the radiosynthesis of [(18)F]56 was then optimized and this radiotracer has been successfully investigated for in vivo PET imaging of melanoma in B16F0- and B16F10-bearing mouse model. The therapeutic efficacy of [(131)I]56 was then evaluated in mice bearing subcutaneous B16F0 melanoma, and a significant slow down in tumoral growth was demonstrated. These data support further development of 56 for PET imaging ((18)F, (124)I) and targeted radionuclide therapy ((131)I) of melanoma using a single chemical structure.

Preparation and biological evaluation of 3-[(76)Br]bromo-α-methyl-L-tyrosine, a novel tyrosine analog for positron emission tomography imaging of tumors

INTRODUCTION

3-[(18)F]fluoro-α-methyl-l-tyrosine ([(18)F]FAMT) is a useful amino acid tracer for positron emission tomography (PET) imaging of malignant tumors. FAMT analogs labeled with (76)Br, a positron emitter with a long half-life (t(1/2)=16.1 h), could potentially be widely used as amino acid tracers for tumor imaging. In this study, 3-[(76)Br]bromo-α-methyl-l-tyrosine ([(76)Br]BAMT) was designed, and its usefulness was evaluated as a novel PET tracer for imaging malignant tumors.

METHODS

In this study, both [(76)Br]BAMT and [(77)Br]BAMT were prepared. The in vitro and in vivo stability of [(77)Br]BAMT was evaluated by HPLC analysis. Cellular uptake and retention of [(77)Br]BAMT and [(18)F]FAMT were evaluated using LS180 colon adenocarcinoma cells. Biodistribution studies were performed in normal mice and in LS180 tumor-bearing mice, and the tumors were imaged with a small-animal PET scanner.

RESULTS

[(77)Br]BAMT was stable in vitro but was catabolized after administration in mice. Cellular accumulation and retention of [(77)Br]BAMT were significantly higher than those of [(18)F]FAMT. In biodistribution studies, the tumor accumulation of [(77)Br]BAMT was higher than that of [(18)F]FAMT. However, some level of debromination was seen, which caused more retention of radioactivity in the blood and organs than was seen with [(18)F]FAMT. PET imaging with [(76)Br]BAMT enabled clear visualization of the tumor, and the whole-body image using [(76)Br]BAMT was similar to that using [(18)F]FAMT.

CONCLUSIONS

[(77)Br]BAMT showed high levels of tumor accumulation, and [(76)Br]BAMT enabled clear visualization of the tumor by PET imaging. Although an improvement in stability is still needed, (76)Br-labeled FAMT analogs could potentially serve as PET tracers for the imaging of malignant tumors.

Use of prechemotherapy positron emission tomography-CT imaging, acquired in the treatment position, to help plan involved nodal radiotherapy for a patient with diffuse large B-cell lymphoma

Fused positron emission tomography/computed tomography (PET-CT) images are increasingly being used to assist radiation oncologists in the definition of treatment volumes for patients with metabolically active tumours. This is the first report in which baseline fluorodeoxyglucose-PET-CT images were acquired in the treatment position in a case of diffuse large B-cell lymphoma and incorporated directly into the radiotherapy treatment planning process. It highlights the potential benefits of using combined 3-D functional and structural imaging for the design of radiation target volumes in patients with aggressive lymphomas that are managed with combined chemo and radiotherapy.

Comparison of ¹³¹I whole-body imaging, ¹³¹I SPECT/CT, and ¹⁸F-FDG PET/CT in the detection of metastatic thyroid cancer

PURPOSE

The aim of this study was to compare (131)I whole-body scintigraphy (WBS), WBS with (131)I single photon emission computed tomography/computed tomography (SPECT/CT), and (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT in the detection of distant metastases of differentiated thyroid cancer (DTC).

METHODS

A total of 140 patients with 258 foci of suspected distant metastases were evaluated. (131)I WBS, (131)I SPECT/CT, and (18)F-FDG PET/CT images were interpreted separately. The final diagnosis was obtained from histopathologic study, serum thyroglobulin level, other imaging modalities, and/or clinical follow-up.

RESULTS

Of the 140 patients with 258 foci, 46 patients with 166 foci were diagnosed as positive for distant metastasis. The sensitivity, specificity, and diagnostic accuracy of each imaging modality were 65, 55, and 59%, respectively, for (131)I WBS; 65, 95, and 85% for (131)I SPECT/CT, respectively; and 61, 98, and 86%, respectively, for (18)F-FDG PET/CT in patient-based analyses. Lesion-based analyses demonstrated that both SPECT/CT and PET/CT were superior to WBS (p<0.001) in all patient groups. SPECT/CT was superior to WBS and PET/CT (p<0.001) in patients who received a single challenge of radioiodine therapy, whereas PET/CT was superior to WBS (p=0.005) and SPECT/CT (p=0.013) in patients who received multiple challenges.

CONCLUSION

Both SPECT/CT and PET/CT demonstrated high diagnostic performance in detecting metastatic thyroid cancer. SPECT/CT was highly accurate in patients who underwent a single challenge of radioiodine therapy. In contrast, (18)F-FDG PET/CT presented the highest diagnostic performance in patients who underwent multiple challenges of radioiodine therapy.

Utility of ¹¹C-choline imaging as a supplement to F-18 FDG PET imaging for detection of thyroid carcinoma

PURPOSE

We present 4 patients with thyroid carcinoma who underwent ¹¹C-choline PET/CT for the detection of their primary tumor and its metastases. Previous F-18 FDG PET had shown no abnormal tracer uptake in the lesions in 3 patients and only mild uptake in 1 patient.

MATERIALS AND METHODS

Four patients aged between 24 and 59 years (2 newly diagnosed and 2 with recurrence) underwent whole-body F-18 FDG PET/CT. The patients then underwent regional ¹¹C-choline PET/CT imaging on a separate day.

RESULTS

All of the lesions in 4 patients were ¹¹C-choline avid except for a few small lung metastases. The SUVmax of the lesions was 7.94 ± 4.93. ¹¹C-choline imaging detected 3 primary tumors in 4 patients, 1 tumor in the tracheal wall in 1 patient, 7 cervical lymph nodes metastases in 3 patients, and several lung metastases in 1 patient.

CONCLUSIONS

¹¹C-choline PET/CT may be a promising supplement to F-18 FDG PET/CT in the detection of thyroid carcinoma and its metastases.

18F-FDG PET/CT as a diagnostic tool in patients with extracervical carcinoma of unknown primary site: a literature review

BACKGROUND

Carcinoma of unknown primary (CUP) represents a heterogeneous group of metastatic malignancies for which no primary tumor site can be identified after extensive diagnostic workup. Failure to identify the primary site may negatively influence patient management. The aim of this review was to evaluate (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) as a diagnostic tool in patients with extracervical CUP.

MATERIALS AND METHODS

A comprehensive literature search was performed and four publications were identified (involving 152 patients) evaluating (18)F-FDG PET/CT in CUP patients with extracervical metastases. All studies were retrospective and heterogeneous in inclusion criteria, study design, and diagnostic workup prior to (18)F-FDG PET/CT.

RESULTS

(18)F-FDG PET/CT detected the primary tumor in 39.5% of patients with extracervical CUP. The lung was the most commonly detected primary tumor site (∼50%). The pooled estimates of sensitivity, specificity, and accuracy of (18)F-FDG PET/CT in the detection of the primary tumor site were 87%, 88%, and 87.5%, respectively.

CONCLUSIONS

The present review of currently available data indicates that (18)F-FDG PET/CT might contribute to the identification of the primary tumor site in extracervical CUP. However, prospective studies with more uniform inclusion criteria are required to evaluate the exact value of this diagnostic tool.

Plasma Epstein-Barr virus DNA screening followed by ¹⁸F-fluoro-2-deoxy-D-glucose positron emission tomography in detecting posttreatment failures of nasopharyngeal carcinoma

BACKGROUND

The authors investigated the clinical implication of plasma Epstein-Barr virus (EBV) DNA assay and (18) F-fluoro-2-deoxy-D-glucose ((18) F-FDG) positron emission tomography (PET) in the detection of recurrent nasopharyngeal carcinoma (NPC).

METHODS

Two hundred forty-five patients with NPC who had previously received treatment and were in a state of remission were monitored prospectively using a plasma EBV DNA assay every 3 to 6 months. (18) F-FDG PET studies were obtained when abnormal EBV DNA or clinically suggestive signs of recurrence were noted.

RESULTS

Thirty-six of 245 patients (14.7%) patients had abnormal EBV DNA tests and underwent PET scans. In the remaining 209 patients, 3658 blood tests were negative. PET scans also were obtained in 5 patients who had undetectable EBV DNA levels but signs that were clinically suggestive of disease recurrence. Subsequent analyses focused on 41 patients who had PET studies. In lesion-based analyses, the sensitivity, specificity, and accuracy of PET by visual interpretation were 81.8%, 77.1%, and 79.2%, respectively, for all 125 lesions. In patient-based analyses, the accuracy of PET by visual interpretation was 51.2%. All 36 patients who had detectable plasma levels of EBV DNA had demonstrable NPC recurrences, whereas no recurrences were noted in 5 patients who had undetectable EBV DNA levels but signs that clinically mimicked a recurrence. Compared with annual PET, the annual cost of blood tests every 3 to 6 months per patient saved approximately 77% ∼ 88% in expenses.

CONCLUSIONS

The plasma EBV DNA assay correctly predicted all NPC recurrences, and PET had high capacity to localize potential lesion sites. The authors concluded that applying the strategy of EBV DNA screening followed by PET scanning may guide appropriate further treatment planning in a cost-effective manner.

PET/CT in cancer research: from preclinical to clinical applications

The identification of genetic and biochemical mechanisms underlying tumor growth and progression along with the unraveling of human genoma provided a plethora of new targets for cancer detection, treatment and monitoring. Simultaneously, the extraordinary development of a number of imaging technologies, including hybrid systems, allowed the visualization of biochemical, molecular and physiological aberrations linked to underlying mutations in a given tumor. In vivo evaluation of complex biological processes such as proliferation, apoptosis, angiogenesis, metastasis, gene expression, receptor-ligand interactions, transport of substrates and metabolism of nutrients in human cancers is feasible using PET/CT and radiolabeled molecular probes. Some of these compounds are in preclinical phases of evaluation whereas others have been already applied in clinical settings. Here we provide prominent examples on how some biological processes and target expression can be visualized by PET/CT in animal tumor models and cancer patients for the noninvasive detection of well-known markers of tumor aggressiveness, invasiveness and resistance to treatment and for the evaluation of tumor response to therapy.

The role of 18F-fluorodeoxyglucose positron emission tomography in thyroid neoplasms

(18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) has established itself as an important imaging modality in many oncological and nononcological specialties and, as a consequence, it is increasingly being used in clinical practice. Since the first report of FDG being taken up by metastatic differentiated thyroid carcinoma (DTC) cells >20 years ago, various groups of investigators have explored the potential role of FDG-PET scanning in patients with benign and malignant thyroid neoplasms. With the increasing demand for FDG-PET scanning, clinicians are faced with the challenge of managing an increasing number of FDG-PET-detected thyroid incidentalomas because their significance remains unclear. The aims of this review are to address some of these issues, specifically, the clinical significance of FDG-PET-detected thyroid incidentalomas, the ability of FDG-PET to characterize thyroid nodules, especially those with indeterminate fine needle aspiration cytology results, and the role of FDG-PET in patients with confirmed primary DTC and with suspected recurrent DTC, by reviewing the current literature.

Current molecular imaging of spinal tumors in clinical practice

Energy metabolism measurements in spinal cord tumors, as well as in osseous spinal tumors/metastasis in vivo, are rarely performed only with molecular imaging (MI) by positron emission tomography (PET). This imaging modality developed from a small number of basic clinical science investigations followed by subsequent work that influenced and enhanced the research of others. Apart from precise anatomical localization by coregistration of morphological imaging and quantification, the most intriguing advantage of this imaging is the opportunity to investigate the time course (dynamics) of disease-specific molecular events in the intact organism. Most importantly, MI represents one of the key technologies in translational molecular neuroscience research, helping to develop experimental protocols that may later be applied to human patients. PET may help monitor a patient at the vertebral level after surgery and during adjuvant treatment for recurrent or progressive disease. Common clinical indications for MI of primary or secondary CNS spinal tumors are: (i) tumor diagnosis, (ii) identification of the metabolically active tumor compartments (differentiation of viable tumor tissue from necrosis) and (iii) prediction of treatment response by measurement of tumor perfusion or ischemia. While spinal PET has been used under specific circumstances, a question remains as to whether the magnitude of biochemical alterations observed by MI in CNS tumors in general (specifically spinal tumors) can reveal any prognostic value with respect to survival. MI may be able to better identify early disease and to differentiate benign from malignant lesions than more traditional methods. Moreover, an adequate identification of treatment effectiveness may influence patient management. MI probes could be developed to image the function of targets without disturbing them or as treatment to modify the target's function. MI therefore closes the gap between in vitro and in vivo integrative biology of disease. At the spinal level, MI may help to detect progression or recurrence of metastatic disease after surgical treatment. In cases of nonsurgical treatments such as chemo-, hormone- or radiotherapy, it may better assess biological efficiency than conventional imaging modalities coupled with blood tumor markers. In fact, PET provides a unique possibility to correlate topography and specific metabolic activity, but it requires additional clinical and experimental experience and research to find new indications for primary or secondary spinal tumors.

Positron emission tomography-computed tomography standardized uptake values in clinical practice and assessing response to therapy

The use of standardized uptake values (SUVs) is now common place in clinical 2-deoxy-2-[(18)F] fluoro-D-glucose (FDG) position emission tomography-computed tomography oncology imaging and has a specific role in assessing patient response to cancer therapy. Ideally, the use of SUVs removes variability introduced by differences in patient size and the amount of injected FDG. However, in practice there are several sources of bias and variance that are introduced in the measurement of FDG uptake in tumors and also in the conversion of the image count data to SUVs. In this article the overall imaging process is reviewed and estimates of the magnitude of errors, where known, are given. Recommendations are provided for best practices in improving SUV accuracy.

Incidental thyroid carcinoma by FDG-PET/CT: a study of clinicopathological characteristics

BACKGROUND

The rising incidence of incidental thyroid carcinoma (ITC) detected during fluoro-2-deoxy-D: -glucose (FDG)-positron emission tomography (PET)/computed tomography (CT) scanning poses a challenge to clinicians. The present study aims to critically evaluate the clinicopathological characteristics of ITC detected by FDG-PET/CT.

METHODS

Among the 557 patients managed at our institution, 40 (7.2%) patients were identified as having ITC. Of these, 22 patients had their tumor detected by FDG-PET/CT (PET group) and 11 by ultrasonography (USG group). Additional bedside ultrasonography ± fine-needle aspiration (FNA) was done in all patients at their clinic visit. The clinicopathological characteristics were compared between the PET and USG groups.

RESULTS

The PET group had significantly more patients with history of nonthyroidal malignancy (P < 0.001). Papillary carcinoma was the most common histological type in both groups. Despite having similar histological and prognostic features including tumor size, tumor multifocality, capsular invasion, extrathyroidal extension, and lymph node metastases, tumor bilaterality (or presence of contralateral tumor focus) was significantly more frequent in the PET than the USG group (P = 0.04). The tumors were also more advanced by the tumor-node-metastasis (TNM) staging system in the PET group (P = 0.021). None of the contralateral tumor foci were evident preoperatively. One patient in the USG group developed metastatic thyroid carcinoma in neck lymph nodes 28 months after thyroid resection.

CONCLUSION

ITC by FDG-PET/CT had higher incidence of tumor bilaterality than those detected by ultrasonography. Total thyroidectomy should be considered for ITC detected by FDG-PET/CT even for tumor size <10 mm.

Quantifying and reducing the effect of calibration error on variability of PET/CT standardized uptake value measurements

The purpose of this study was to measure the errors introduced by regular calibration of PET/CT scanners and to minimize the effect of calibration error on standardized uptake value measurements.

METHODS

Global calibration factors from 2 PET/CT scanners were recorded for 3.5 and 1.8 y, comparing manufacturer-recommended protocols with modified protocols to evaluate error contributions due to operator-influenced procedures. Dose calibrator measurements were evaluated using National Institute of Standards and Technology-traceable sources.

RESULTS

Dose calibrator variability was less than 1%, although there was a consistent bias. Global scaling variability was reduced from 6% to 4% for scanner 1 and from 11% to 4% for scanner 2 when quality assurance and quality control procedures were applied to the calibration protocol. When calibrations were done using a (68)Ge/(68)Ga phantom, the variability for both scanners was reduced to approximately 3%.

CONCLUSION

Applying quality assurance and quality control procedures to scanner calibration reduces variability, but there is a still a residual longitudinal scanner variability of 3%-4%. The procedures proposed here reduce the impact of operator error on scanner calibration and thereby minimize longitudinal variability in standardized uptake value measurements.

Measuring response to therapy using FDG PET: semi-quantitative and full kinetic analysis

Purpose

Imaging with positron emission tomography (PET) using ¹⁸F-2-fluoro-2-deoxy-D-glucose (FDG) plays an increasingly important role for response assessment in oncology. Several methods for quantifying FDG PET results exist. The goal of this study was to analyse and compare various semi-quantitative measures for response assessment with full kinetic analysis, specifically in assessment of novel therapies.

Methods

Baseline and response dynamic FDG studies from two different longitudinal studies (study A: seven subjects with lung cancer and study B: six subjects with gastrointestinal cancer) with targeted therapies were reviewed. Quantification of tumour uptake included full kinetic methods, i.e. nonlinear regression (NLR) and Patlak analyses, and simplified measures such as the simplified kinetic method (SKM) and standardized uptake value (SUV). An image-derived input function was used for NLR and Patlak analysis.

Results

There were 18 and 9 lesions defined for two response monitoring studies (A and B). In all cases there was excellent correlation between Patlak- and NLR-derived response (R² > 0.96). Percentage changes seen with SUV were significantly different from those seen with Patlak for both studies (p < 0.05). After correcting SUV for plasma glucose, SUV and Patlak responses became similar for study A, but large differences remained for study B. Further analysis revealed that differences in responses amongst methods in study B were primarily due to changes in the arterial input functions.

Conclusion

Use of simplified methods for assessment of drug efficacy or treatment response may provide different results than those seen with full kinetic analysis.

Methodological aspects of multicenter studies with quantitative PET

Quantification of whole-body FDG PET studies is affected by many physiological and physical factors. Much of the variability in reported standardized uptake value (SUV) data seen in the literature results from the variability in methodology applied among these studies, i.e., due to the use of different scanners, acquisition and reconstruction settings, region of interest strategies, SUV normalization, and/or corrections methods. To date, the variability in applied methodology prohibits a proper comparison and exchange of quantitative FDG PET data. Consequently, the promising role of quantitative PET has been demonstrated in several monocentric studies, but these published results cannot be used directly as a guideline for clinical (multicenter) trials performed elsewhere. In this chapter, the main causes affecting whole-body FDG PET quantification and strategies to minimize its inter-institute variability are addressed.

Gynecological cancers

The clinical problems raised in patients presenting with all forms of gynecological malignancy are currently addressed using conventional cross-sectional imaging, usually MRI. In general, F-18 FDG PET-CT has not been shown to have a clinical role in any of these cancers at presentation, although studies are under way to use this form of metabolic imaging to predict prognosis and the response to treatment. Although F-18 FDG PET-CT is superior to conventional imaging techniques, it is only moderately sensitive in demonstrating lymph node metastasis preoperatively, and is inadequate for local staging of patients with endometrial cancer. In ovarian cancer, F-18 FDG PET-CT provides an accurate assessment of the extent of disease, particularly in areas difficult to assess for metastases by CT and MRI such as the abdomen and pelvis, mediastinum, and supraclavicular region. F-18 FDG PET-CT is a sensitive method of detecting pelvic and para-aortic lymph nodal disease in cervical cancer, and appears to be superior to MRI and CT despite the limitations in identifying small foci of disease. In the main, as elsewhere in patients with cancer, the value of PET-CT is in identifying and defining the extent of recurrent disease, in distinguishing between posttreatment fibrosis and recurrence, and possibly in monitoring response to therapy.

Size-dependent thresholding as an optimal method for tumor volume delineation on positron emission tomography-computed tomography: A Phantom study

BACKGROUND

Use of a fixed threshold value for tumor volume delineation in positron emission tomography (PET) images will ignore the effect of size of the lesion and source to background ratio (SBR). The purpose of this Phantom study was to evaluate the effect of the size of the lesion and SBR on the threshold to be used for PET tumor volume delineation.

MATERIALS AND METHODS

Phantom used in the study comprised a sphere-cylinder assembly containing six spheres of different inner diameters (1.10, 1.35, 1.44, 1.50, 1.83 and 1.93 cm) with inner volumes of 0.70, 1.30, 1.50, 1.77, 3.22 and 3.82 cm(3), respectively. The scans were acquired with SBR of 6:01, 7:01, 8:01 and 10:01. These SBRs were calculated from 42 patients with lymphoma to simulate clinical images. PET tumor volume was calculated using RT_Image software at different threshold values (40, 45, 50, 55, 60, 65, 70 and 75% of SUV(max)) for each sphere at different SBRs. The threshold intensity value at which the calculated volume was nearly equal to actual volume of spheres was considered as the standardized threshold intensity (STI) value.

RESULTS

STI values depended on the diameter of the sphere and not on the SBR. It is found that 40% threshold is suitable for calculating the volume of any lesion with diameter greater than 1.83 cm, 60% for diameter greater than 1.35 cm but less than 1.83 cm, and 75% for diameter less than 1.35 cm.

CONCLUSION

Size-dependent thresholding is an accurate and reproducible method of tumor volume delineation on PET-computed tomography (CT).

18F-FDG PET/CT for the prediction and detection of local recurrence after radiofrequency ablation of malignant lung lesions

The utility of (18)F-FDG PET/CT for response assessment in malignant lung tumors treated with radiofrequency ablation (RFA) and for the detection and prediction of local recurrence was investigated.

METHODS

Between December 17, 2003, and April 9, 2008, 68 consecutive patients (mean age, 68 y) with 94 pulmonary lesions, including metastases (n = 38) and primary lung cancers (n = 44), underwent RFA. Because of inadequate imaging follow-up in 12 patients, only 82 lesions were analyzed (CT scans, n = 82; (18)F-FDG PET/CT scans, n = 62). The median follow-up was 25 mo (range, 12-66 mo). A baseline study was defined as (18)F-FDG PET/CT performed no more than 3 mo before RFA. The first postablation scan was defined as PET/CT performed between 1 and 4 mo after RFA; additional follow-up studies were obtained in some cases between 6 and 12 mo after RFA. The unidimensional maximum diameter of the lesion was recorded on a pretherapy diagnostic CT scan or on the CT component of a pretherapy (18)F-FDG PET/CT scan, whichever was obtained most recently, using lung windows. Maximum standardized uptake values (SUVs) were recorded for all lesions imaged by (18)F-FDG PET/CT. (18)F-FDG uptake patterns on post-RFA scans were classified as favorable or unfavorable. Survival and recurrence probabilities were estimated using the Kaplan-Meier method. Uni- and multivariate analyses were also performed.

RESULTS

Before RFA, factors predicting greater local recurrence-free survival included initial lesion size less than 3 cm (P = 0.01) and SUV less than 8 (P = 0.02), although the latter was not an independent predictor in multivariate analysis. Treated metastases recurred less often than treated primary lung cancers (P = 0.03). Important post-RFA factors that related to reduced recurrence-free survival included an unfavorable uptake pattern (P < 0.01), post-RFA SUV (P < 0.01), and an increase in SUV over time after ablation (P = 0.05).

CONCLUSION

(18)F-FDG PET/CT parameters on both preablation and postablation scans may predict local recurrence in patients treated with RFA for lung metastases and primary lung cancers.

Role of 18F-FDG PET in detecting primary site in the patient with primary unknown carcinoma

The aim of this study was to verify the effectiveness of positron emission tomography (PET) in detecting primary sites in carcinoma of unknown primary (CUP) patients. In this study, CUP represented a group of heterogeneous tumors that shared the clinical manifestation of metastatic carcinoma with no obvious primary site at the time of first diagnosis, which included clinical investigations, computed tomography, magnetic resonance imaging and panendoscopy. We reviewed the records of 24 patients with CUP between January 1995 and December 2009. The patients who demonstrated additional tracer uptake sites other than previously known metastatic lesions by PET scan were done direct biopsies for the sites of accumulation. Patients who had a negative PET scan or for whom the primary site could not be identified by direct biopsies underwent examination under anesthesia of the at-risk occult tumor sites. PET scan demonstrated focal accumulation suspicious for primary tumor in 12 (50.0%) of 24 patients: tonsil 5, nasopharynx 3, hypopharynx 1, tongue 1, larynx 1, and maxillary sinus 1. A subsequent biopsy of these sites revealed primary cancer in 9 (37.5%) of 24 patients: tonsil 5, nasopharynx 1, hypopharynx 1, tongue 1, and maxillary sinus 1. In the remaining three patients, no malignant cells were found by the biopsy of the accumulated area: nasopharynx 2, larynx 1. PET scans increase the yield of primary tumor by 37.5%. The sensitivity, specificity for PET scan were 80.8, 76.9%, respectively. PET scanning is useful in detecting primary cancer of CUP patients.

Effects of blood glucose level on FDG uptake by liver: a FDG-PET/CT study

In FDG-PET for abdominal malignancy, the liver may be assumed as an internal standard for grading abnormal FDG uptake both in early images and in delayed images. However, physiological variables of FDG uptake by the liver, especially the effects of blood glucose level, have not yet been elucidated.

METHODS

FDG-PET studies of 70 patients examined at 50 to 70 min after injection (60 ± 10 min: early images) and of 68 patients examined at 80 to 100 min after injection (90 ± 10 min: delayed images) were analyzed for liver FDG uptake. Patients having lesions in the liver, spleen and pancreas; patients having bulk tumor in other areas; and patients early after chemotherapy or radiotherapy were excluded; also, patients with blood glucose level over 125 mg/dl were excluded.

RESULTS

Mean standardized uptake value (SUV) of the liver, blood glucose level and sex showed no significant differences between early images and delayed images. However, liver SUV in the delayed image showed a larger variation than that in the early image and showed significant correlation to blood glucose level. The partial correlation coefficient between liver SUV and blood glucose level in the delayed image with adjustment for sex and age was 0.73 (P < .0001). Multivariate regression coefficient (95% confidence interval) of blood glucose was 0.017 (0.013-0.021).

CONCLUSION

Blood glucose level is an important factor affecting the normal liver FDG uptake in nondiabetic patients. In the case of higher glucose level, liver FDG uptake is elevated especially in the delayed image. This may be due to the fact that the liver is the key organ responsible for glucose metabolism through gluconeogenesis and glycogen storage.

Improved cancer therapy and molecular imaging with multivalent, multispecific antibodies

Antibodies are highly versatile proteins with the ability to be used to target diverse compounds, such as radionuclides for imaging and therapy, or drugs and toxins for therapy, but also can be used unconjugated to elicit therapeutically beneficial responses, usually with minimal toxicity. This update describes a new procedure for forming multivalent and/or multispecific proteins, known as the dock-and-lock (DNL) technique. Developed as a procedure for preparing bispecific antibodies capable of binding divalently to a tumor antigen and monovalently to a radiolabeled hapten-peptide for pretargeted imaging and therapy, this methodology has the flexibility to create a number of other biologic agents of therapeutic interest. A variety of constructs, based on anti-CD20 and CD22 antibodies, have been made, with results showing that multispecific antibodies have very different properties from the respective parental monospecific antibodies. The technique is not restricted to antibody combination, but other biologics, such as interferon-alpha2b, have been prepared. These types of constructs not only allow small biologics to be sustained in the blood longer, but also to be selectively targeted. Thus, DNL technology is a highly flexible platform that can be used to prepare many different types of agents that could further improve cancer detection and therapy.

A systematic review of PET and PET/CT in oncology: a way to personalize cancer treatment in a cost-effective manner?

BACKGROUND

A number of diagnostic tests are required for the detection and management of cancer. Most imaging modalities such as computerized tomography (CT) are anatomical. However, positron emission tomography (PET) is a functional diagnostic imaging technique using compounds labelled with positron-emitting radioisotopes to measure cell metabolism. It has been a useful tool in studying soft tissues such as the brain, cardiovascular system, and cancer. The aim of this systematic review is to critically summarize the health economic evidence of oncologic PET in the literature.

METHODS

Eight electronic databases were searched from 2005 until February 2010 to identify economic evaluation studies not included in previous Health Technology Assessment (HTA) reports. Only full health economic evaluations in English, French, or German were considered for inclusion. Economic evaluations were appraised using published quality criteria for assessing the quality of decision-analytic models. Given the variety of methods used in the health economic evaluations, the economic evidence has been summarized in qualitative form.

RESULTS

From this new search, 14 publications were identified that met the inclusion criteria. All publications were decision-analytic models and evaluated PET using Fluorodeoxyglucose F18 (FDG-PET). Eight publications were cost-effectiveness analyses; six were cost-utility analyses. The studies were from Australia, Belgium, Canada, France, Italy, Taiwan, Japan, the Netherlands, the United Kingdom, and the United States. In the base case analyses of these studies, cost-effectiveness results ranged from dominated to dominant. The methodology of the economic evaluations was of varying quality. Cost-effectiveness was primarily influenced by the cost of PET, the specificity of PET, and the risk of malignancy.

CONCLUSIONS

Owing to improved care and less exposure to ineffective treatments, personalized medicine using PET may be cost-effective. However, the strongest evidence for the cost-effectiveness of PET is still in the staging of non-small cell lung cancer. Management decisions relating to the assessment of treatment response or radiotherapy treatment planning require further research to show the impact of PET on patient management and its cost-effectiveness. Because of the potential for increased patient throughput and the possible greater accuracy, the cost-effectiveness of PET/CT may be superior to that of PET. Only four studies of the cost-effectiveness of PET/CT were found in this review, and this is clearly an area for future research.