Positron emission tomography: clinical applications in oncology. Part 1

Diagnosis of cholangiocarcinoma in primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic inflammatory disease of the hepatobiliary system characterized by chronic inflammation, progressive fibrosis, stricture formation and destruction of extrahepatic and intrahepatic bile ducts. Areas covered: The increased incidence of cholangiocarcinoma (CCA) in PSC has been well documented and can be explained by the continuous inflammation in the biliary tree leading to an enhanced dysplasia-carcinoma sequence. Although PSC patients may progress to liver cirrhosis; CCA most commonly occurs between the ages of 30 and 45 years when cirrhosis has not yet developed. Therefore, CCA in patients with PSC occurs earlier than in patients without PSC. Expert commentary: Despite improvement in diagnostic methods and devices, the dilemma of diagnosing CCA in patients with PSC has not been solved yet and needs further investigation.

Fat-Containing Hypermetabolic Masses on FDG PET/CT: A Spectrum of Benign and Malignant Conditions

OBJECTIVE

This article focuses on identifying the imaging appearances of hypermetabolic fatty masses and masslike lesions on PET/CT and understanding the diagnostic challenges radiologists may face while interpreting findings of these lesions on PET/CT. This article provides an approach to aid in the diagnosis of these lesions and the appropriate management of patients.

CONCLUSION

Both malignant and benign fat-containing masses and masslike lesions can show hypermetabolic activity on PET/CT. Although the differential diagnosis is broad, clinical history, anatomic location, and knowledge of anatomic variants and imaging features can help radiologists avoid misinterpretation of benign fatty lesions as malignancy.

Assessment of Therapy Response by FDG PET in Infection and Inflammation

Positron emission tomography (PET) is a well-known imaging modality in assessing the treatment response to chemotherapy or radiotherapy in various malignancies. A systematic review of the literature reveals a few publications reporting evaluation of the treatment response in benign conditions using PET/computed tomography. PET holds a promising future role in the follow-up of inflammatory or infectious diseases. In this article, [(18)F]Fluorodeoxyglucose PET as a tool in the evaluation, treatment, and follow-up of infectious and inflammatory diseases is discussed.

PET/CT today and tomorrow in veterinary cancer diagnosis and monitoring: fundamentals, early results and future perspectives

Functional imaging using positron emission tomography (PET) plays an important role in the diagnosis, staging, image-guided treatment planning and monitoring of malignant diseases. PET imaging complements conventional anatomical imaging such as computed tomography (CT) and magnetic resonance imaging (MRI). The strength of CT scanning lies in its high spatial resolution, allowing for anatomical characterization of disease. PET imaging, however, moves beyond anatomy and characterizes tissue based on functions such as metabolic rate. Combined PET/CT scanners were introduced commercially in 2001 and a number of technological advancements have since occurred. Radiolabelled tracers such as (18)F-fluorodeoxyglucose (FDG) and (18)F-fluorothymidine (FLT) allow visualization of various metabolic processes within cancer cells. Many studies in human oncology evaluating the utility of PET/CT have demonstrated clinical benefits. Few veterinary studies have been performed, but initial studies show promise for improved detection of malignancy, more thorough staging of canine cancer and determination of early response and disease recrudescence.

¹⁸F-FDG and ¹¹C-MET positron emission tomography findings of cutaneous mast cell tumor in a dog

A 12-year-old intact male Maltese dog presented with an inguinal mass. Histopathology revealed a grade III mast cell tumor. Computed tomography demonstrated pulmonary and inguinal nodules and masses. Chemotherapy was performed using a vinblastine/prednisone protocol, and the inguinal mass disappeared 5 weeks later. Use of 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) and (L)-[methyl- ¹¹C]methionine (¹¹C-MET)-positron emission tomography (PET) demonstrated hypermetabolic areas in the lungs and inguinal region one week after initial chemotherapy. The standardized uptake values of ¹⁸F-FDG were not different between lung and inguinal lesions; however, the inguinal lesion had a higher ¹¹C-MET standardized uptake value than the lung lesions. The hypermetabolic area was still visible on the second ¹⁸F-FDG-PET scan despite the disappearance of the mass. This is the first report of ¹¹C-MET-PET findings associated with a cutaneous mast cell tumor in a dog.

(18)F-FDG PET analysis of schwannoma: increase of SUVmax in the delayed scan is correlated with elevated VEGF/VPF expression in the tumors

OBJECTIVE

In order to clarify the increased 2-deoxy-2-fluoro-(18)F-D: -glucopyranose ((18)F-FDG) accumulation in schwannoma by positron emission tomography (PET) analysis, immunohistochemical analysis for the factors involved in glucose transportation and vascular formation was performed.

MATERIALS AND METHODS

Twenty-six patients with schwannoma (13 men and 13 women) with ages ranging from 27 to 75 years, who received whole body (18)F-FDG PET scan, were enrolled for the present study. The retention index (RI) was calculated by dividing the increase in the standardized uptake value (SUVmax) at the delayed scan by the SUVmax in the early scan. SUVmax and RI were compared with the histologic variables, including the expression of glucose transporters 1 and 3, hexokinase II, vascular endothelial growth factor/vascular permeability factor (VEGF/VPF), and microvascular density shown by CD31 immunohistochemistry.

RESULTS

Mean SUVmax values in the early and delayed scans were 2.64 +/- 1.47 and 2.71 +/- 1.57 (mean +/- SD), respectively. RI was -2.5 +/- 21 (percentage). SUVmax showed a positive correlation with the tumor size (tumor size <5 cm, 2.06 +/- 0.72; >5 cm, 3.95 +/- 1.89; p < 0.05) and the microvascular density (negative density, 2.16 +/- 1.12; positive density, 3.56 +/- 1.67; p < 0.05). RI correlated with VEGF/VPF expression in the tumors (negative expression, -11 +/- 6.1; positive expression, 13 +/- 8.1; p < 0.05). Other factors showed no correlation with SUVmax or RI.

CONCLUSIONS

Microvascular density and vascular permeability of the tumor are suggested to affect the enhanced (18)F-FDG accumulation in schwannoma.

Adrenocortical Positron Emission Tomography/PET-CT Imaging

The frequency for detecting asymptomatic adrenal masses is increasing because of the common use of computed tomography and MR imaging in the practice of medicine. CT and MR imaging have played an important role in defining certain physiologic and pathologic ingredients of the adrenal glands; however, it is sometimes difficult to characterize adrenal masses with CT or MR imaging alone. In such cases, further characterization of the adrenal masses can be achieved using functional imaging modalities. Positron emission tomography (PET) using 18-F-fluorodeoxyglucose (FDG) has performed well in the evaluation and management of various malignant conditions. FDG-PET has also shown excellent results in the evaluation of primary and metastatic malignant adrenal disease with poor differentiation. This article discusses in detail various PET radiopharmaceutics which can be used for adrenocortical imaging.

Targeting of VX2 rabbit liver tumor by selective delivery of 3-bromopyruvate: a biodistribution and survival study

The aim of this study was to determine the biodistribution and tumor targeting ability of (14)C-labeled 3-bromopyruvate ([(14)C]3-BrPA) after i.a. and i.v. delivery in the VX2 rabbit model. In addition, we evaluated the effects of [(14)C]3-BrPA on tumor and healthy tissue glucose metabolism by determining (18)F-deoxyglucose (FDG) uptake. Last, we determined the survival benefit of i.a. administered 3-BrPA. In total, 60 rabbits with VX2 liver tumor received either 1.75 mM [(14)C]3-BrPA i.a., 1.75 mM [(14)C]3-BrPA i.v., 20 mM [(14)C]3-BrPA i.v., or 25 ml of phosphate-buffered saline (PBS). All rabbits (with the exception of the 20 mM i.v. group) received FDG 1 h before sacrifice. Next, we compared survival of animals treated with i.a. administered 1.75 mM [(14)C]3-BrPA in 25 ml of PBS (n = 22) with controls (n = 10). After i.a. infusion, tumor uptake of [(14)C]3-BrPA was 1.8 +/- 0.2% percentage of injected dose per gram of tissue (%ID/g), whereas other tissues showed minimal uptake. After i.v. infusion (1.75 mM), tumor uptake of [(14)C]3-BrPA was 0.03 +/- 0.01% ID/g. After i.a. administration of [(14)C]3-BrPA, tumor uptake of FDG was 26 times lower than in controls. After i.v. administration of [(14)C]3-BrPA, there was no significant difference in tumor FDG uptake. Survival analysis showed that rabbits treated with 1.75 mM 3-BrPA survived longer (55 days) than controls (18.6 days). Intra-arterially delivered 3-BrPA has a favorable biodistribution profile, combining a high tumor uptake resulting in blockage of FDG uptake with no effects on healthy tissue. The local control of the liver tumor by 3-BrPA resulted in a significant survival benefit.

Prognostic value of preoperative positron emission tomography in resected stage I non-small cell lung cancer

PURPOSE

Approximately 20 to 40% of patients with surgically resected stage I non-small cell lung cancer (NSCLC) will develop recurrent disease. Positron emission tomography (PET) with 2-[18F] fluoro-2-deoxy-D-glucose (FDG) is used often in staging NSCLC. We conducted this study to determine whether the preoperative maximum tumor standardized uptake value (SUVmax) was associated with recurrence in patients with resected stage I NSCLC.

PATIENTS AND METHODS

We identified consecutive patients who underwent curative surgical resection for stage I NSCLC between 1999 and 2003 who had preoperative FDG-PET imaging. Patients were divided into two cohorts based on SUVmax above or below the median for the group. Recurrence rates were estimated by the Kaplan-Meier method and overall survival was analyzed as a secondary end point.

RESULTS

Of 136 patients who met inclusion criteria, 77 (57%) had T1 and 59 (43%) had T2 tumors. The median follow-up time was 46 months and 32 patients had a disease recurrence. The median SUVmax was 5.5. The 5-year estimates of recurrence rates for patients with low and high SUVmax were 14% and 37%, respectively (p = 0.002), with 5-year overall survivals of 74% and 53%, respectively (p = 0.006). In multivariate analyses based on SUVmax, T-classification, age, and histology, high SUVmax was independently associated with recurrence (p = 0.002) and mortality (p = 0.041).

CONCLUSION

High SUVmax (>or=5.5) on preoperative FDG-PET is an independent predictor of relapse and death in resected stage I NSCLC. Prospective trials of adjuvant chemotherapy in patients with stage I NSCLC and high SUVmax should be considered.

Advanced imaging for veterinary cancer patients

This article presents an update on the recent advances made in veterinary advanced imaging specifically with regard to cross-sectional modalities (CT and MRI) and nuclear medicine (positron emission tomography [PET] and PET/CT). A brief summary of technical improvements and a review of recent literature are included to provide an overview of the progress made in this important element of the practicing veterinary oncologist's repertoire. An in-depth summary of PET is also included to introduce the technical aspects and potential clinical and research applications of this novel imaging modality in veterinary medicine.

Multicentre assessment and monitored use of [18F]FDG-PET in oncology: the Spanish experience

PURPOSE

The aim of this study was to evaluate the diagnostic effectiveness of [(18)F]FDG-PET in oncological diseases and to assess its clinical utility and impact (on the clinical and therapeutic management of these patients). This health technology assessment was performed in Spain, using the monitored use (MU) procedure.

METHODS

A multicentre and prospective follow-up study was performed in a non-consecutive sample of oncological patients who were examined with PET and other conventional diagnostic tests. A protocol for this MU method (PET-MU protocol) was developed, including the three forms used to collect all the information. Enrollment of new patients began in June 2002 and continued until August 2004. A descriptive analysis and an evaluation of the diagnostic effectiveness of FDG-PET were performed.

RESULTS

The study population comprised 2,824 oncological patients (the third form relating to follow-up was completed for only 967 of these patients) from 100 Spanish hospitals and 16 PET centres. Seventy-nine percent of cases met the clinical requirements of the PET-MU protocol. Global diagnostic parameters of PET performance and their 95% CI values were as follows: sensitivity 86% (82-89%), specificity 83% (79-86%), positive and negative predictive values 87% (83-90%) and 82% (77-85%) respectively, diagnostic accuracy 84% (82-87%) and diagnostic odds ratio 28.75 (19.75-41.84). PET detected unsuspected new lesions in 39% of patients and avoided other unnecessary diagnostic techniques and treatments in 69% of cases. In 88% of cases, PET was considered useful by the physicians who asked for the PET tests (it was deemed decisive in 30% and very useful in almost 37%).

CONCLUSION

This PET-MU study has confirmed the high diagnostic effectiveness of FDG-PET for oncological indications and demonstrates that it has a great influence on the clinical and therapeutic management of patients.

Age-Related Changes in the Metabolic Activity and Distribution of the Red Marrow as Demonstrated by 2-Deoxy-2-[F-18]fluoro-d-glucose-Positron Emission Tomography

OBJECTIVES

The objective of the study was to determine age-related changes occurring in red marrow with regard to its distribution and the degree of its metabolic activity by whole-body 2-deoxy-2-[F-18]fluoro-D-glucose (FDG)-positron emission tomography (PET).

METHODS

This retrospective study included 112 patients (56 male, 56 female, mean age 40 years, range 2-85) who underwent whole-body FDG-PET scans for assessment of disorders that were determined not to affect red marrow activity. These patients were categorized into the following groups with equal gender distribution: 0-15 years (12 individuals), 16-25 years (20), 26-35 years (10), 36-45 years (20), 46-55 years (14), 56-65 years (16), 66-75 years (14), and 76-85 years (6). Whole-body FDG-PET images were performed at 60 min after the intravenous administration of 0.14 mCi/kg of FDG. By employing a dedicated whole-body PET scanner. Maximal standardized uptake value (SUV(max)) was calculated from three consecutive transverse sections of the upper thirds of the humeri and femora, manubrium of the sternum, 12th thoracic and 5th lumbar vertebra and anterior superior iliac crests of the pelvis. All available results from other imaging examinations [magnetic resonance imaging (MRI), computed tomography (CT), and conventional radiolography], laboratory data, biopsies, and the clinical course of these subjects were reviewed to make certain that the bone marrow sites examined were free of any known pathologies.

RESULTS

SUV(max) in the extremities showed significant decline with aging (correlation coefficient of -0.60 to -0.67, p < 0.01). In contrast, a weak correlation was noted in the axial skeletal activity with advancing age (correlation coefficient of -0.28 to -0.48, p < 0.05).

CONCLUSIONS

These data suggest that FDG metabolic activity of the red marrow in the extremities decline significantly with normal aging, while that of the axial skeleton show minimal decrease related to this biologic phenomenon. These findings are of value in assessing the effects of hematological and other disorders in the distribution and the metabolic activity of this important tissue and testing therapeutic interventions that are employed for treating such maladies.

Recent evidences of the use of 18F-fluorodeoxyglucose positron emission tomography in the management of colorectal cancer

Positron emission tomography is considered a potentially useful diagnostic tool in the management of a variety of malignancies. It has been used for staging, evaluation of recurrent and metastatic disease, evaluation of tumoral response to neoadjuvant therapy, and providing prognostic information. However, some data are available about its definitive role in the colorectal cancer population. In this review, the most recent evidences and future perspectives are presented for the use of the 18F-fluorodeoxyglucose positron emission tomography in the management of patients with colorectal cancer.

Cancer Imaging and Therapy with Bispecific Antibody Pretargeting

This article reviews recent preclinical and clinical advances in the use of pretargeting methods for the radioimmunodetection and radioimmunotherapy of cancer. Whereas directly-labeled antibodies, fragments, and subfragments (minibodies and other constructs) have shown promise in both imaging and therapy applications over the past 25 years, their clinical adoption has not fulfilled the original expectations due to either poor image resolution and contrast in scanning or insufficient radiation doses delivered selectively to tumors for therapy. Pretargeting involves the separation of the localization of tumor with an anticancer antibody from the subsequent delivery of the imaging or therapeutic radionuclide. This has shown improvements in both imaging and therapy by overcoming the limitations of conventional, or 1-step, radioimmunodetection or radioimmunotherapy. We focus herein on the use of bispecific antibodies followed by radiolabeled peptide haptens as a new modality of selective delivery of radionuclides for the imaging and therapy of cancer. Our particular emphasis in pretargeting is the use of bispecific trimeric (3 Fab's) recombinant constructs made by a modular method of antibody and protein engineering of fusion molecules called Dock and Lock (DNL).

Brain Abnormalities Detected on Whole-Body18F-FDG PET in Cancer Patients: Spectrum of Findings

OBJECTIVE

The purpose of this article is to discuss and show examples of the PET appearance of common brain abnormalities that radiologists encounter when interpreting whole-body 18F-FDG PET examinations of cancer patients.

CONCLUSION

Knowledge of the PET appearance of various brain abnormalities can yield diagnostically relevant information in cancer patients. Detection of brain abnormalities on whole-body PET often requires adjusting window settings to reduce the intensity of normal brain FDG activity. Often, close correlation of PET/CT and MRI with clinical history offers the most complete radiologic diagnosis.

Design of radiolabelled ligands for the imaging and treatment of cancer

The specialised medical field of Nuclear Medicine is concerned with the use of unsealed sources of radioactivity either to diagnose or treat a range of diseases. In this regard it can be distinguished from the field of Radiotherapy which uses sealed radioactive sources for treatment. The range of diseases in which Nuclear Medicine plays a role is wide and includes, among others, the fields of microbiology, endocrinology, neurology, oncology and cardiovascular medicine. However, cancer probably represents the most important and growing area of application for this modality. Nuclear Medicine employs radiopharmaceuticals. These are radiolabelled ligands that have the ability to interact with molecular targets that are relevant in the aetiology or treatment of cancer and in many respects Nuclear Medicine can be considered the archetype for the application of 'Molecular Medicine'. An example of a Nuclear Medicine Positron Emission Tomography (PET) scan is shown in Fig. 2. There is great interest in developing new radioligands that allow us to image the expression of the ever increasing range of biological pathways being discovered in the post-genomic area. Designing effective radiopharmaceuticals, however, requires an understanding of a number of radiopharmaceutical sciences including aspects of chemistry, physics, cell and molecular biology, and physiology.

Role of PET/PET-CT in the management of sarcomas

Positron emission tomography (PET) is a functional diagnostic imaging technique that provides very different information from that obtainable with other imaging modalities. The most widely used radiotracer is F-18 fluoro-2-deoxy-D-glucose (FDG), which is an analog of glucose. The FDG uptake in cells is directly proportional to glucose metabolism, which is increased many times in malignant cells. FDG-PET is now the standard of care in initial staging, monitoring the response to therapy and management of various cancers (e.g., breast cancer, lung cancer and lymphoma). However, the paucity of anatomical landmarks on PET images makes a consistent hardware fusion to anatomical cross-sectional data extremely useful. The introduction of combined PET-computer tomography (CT) scanners, which provide not only functional, but also structural information leading to a detection of subcentimeter lesions, made this technique useful in the early detection of the disease process and decreasing false-positive lesions. The aim of this article is to review the clinical applications (i.e., diagnosis, staging, evaluation of treatment response and restaging) using PET in patients with bone and soft-tissue sarcoma.

MicroPET investigation of chronic long-term neurotoxicity from heavy ion irradiation

Positron emission tomography (PET) permits imaging of the regional biodistribution and pharmacokinetics of compounds labeled with short-lived positron-emitting isotopes. It has enabled evaluation of neurochemical systems in the living human brain, including effects of toxic substances. MicroPET devices allow studies of the rat brain with a spatial resolution of approximately 2 mm. This is much poorer resolution than obtained using ex vivo autoradiography. However, animals need not be euthanized before imaging, so repeat studies are possible. This in principle allows the effects of toxic insults to be followed over the lifetime of an individual animal. We used microPET to evaluate brain metabolic effects of irradiation with high-energy heavy ions (HZE radiation), a component of the space radiation environment, on regional glucose metabolism. A significant fraction of neurons would be traversed by these densely ionizing particles during a Mars mission, and there is a need to estimate human neurological risks of prolonged voyages beyond the geomagnetosphere. Rats were irradiated with 56Fe (600 MeV/n) ions at doses up to 240 cGy. At 9 months post-irradiation we did not detect alterations in regional accumulation of the glucose analog [18F]2-deoxy-2-fluoro-D-glucose. This may indicate that damage to the brain from HZE particles is less severe than feared. However, because radiation-induced alterations in some behaviors have been documented, it may reflect insensitivity of baseline cerebral glucose metabolism to HZE radiation. These studies will facilitate design of future studies of chronic, long-term exposure to both therapeutic and abused drugs using microPET.