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

PET/CT and breast cancer

This paper summarises the current status of PET/CT in relation to breast cancer.

Preclinical dynamic 18F-FDG PET - tumor characterization and radiotherapy response assessment by kinetic compartment analysis

BACKGROUND

Non-invasive visualization of tumor biological and molecular processes of importance to diagnosis and treatment response is likely to be critical in individualized cancer therapy. Since conventional static (18)F-FDG PET with calculation of the semi-quantitative parameter standardized uptake value (SUV) may be subject to many sources of variability, we here present an approach of quantifying the (18)F-FDG uptake by analytic two-tissue compartment modeling, extracting kinetic tumor parameters from dynamic (18)F-FDG PET. Further, we evaluate the potential of such parameters in radiotherapy response assessment.

MATERIAL AND METHODS

Male, athymic mice with prostate carcinoma xenografts were subjected to dynamic PET either untreated (n=8) or 24 h post-irradiation (7.5 Gy single dose, n=8). After 10 h of fasting, intravenous bolus injections of 10-15 MBq (18)F-FDG were administered and a 1 h dynamic PET scan was performed. 4D emission data were reconstructed using OSEM-MAP, before remote post-processing. Individual arterial input functions were extracted from the image series. Subsequently, tumor (18)F-FDG uptake was fitted voxel-by-voxel to a compartment model, producing kinetic parameter maps.

RESULTS

The kinetic model separated the (18)F-FDG uptake into free and bound tracer and quantified three parameters; forward tracer diffusion (k(1)), backward tracer diffusion (k(2)), and rate of (18)F-FDG phosphorylation, i.e. the glucose metabolism (k(3)). The fitted kinetic model gave a goodness of fit (r(2)) to the observed data ranging from 0.91 to 0.99, and produced parametrical images of all tumors included in the study. Untreated tumors showed homogeneous intra-group median values of all three parameters (k(1), k(2) and k(3)), whereas the parameters significantly increased in the tumors irradiated 24 h prior to (18)F-FDG PET.

CONCLUSIONS

This study demonstrates the feasibility of a two-tissue compartment kinetic analysis of dynamic (18)F-FDG PET images. If validated, extracted parametrical maps might contribute to tumor biological characterization and radiotherapy response assessment.

Physiology and pathophysiology of incidental findings detected on FDG-PET scintigraphy

A routine feature of positron emission tomography/computed tomography (PET/CT) imaging is whole-body acquisition that results in many unexpected findings identified outside of the primary region of abnormality. Furthermore, (18)F-fluorodeoxyglucose (FDG) is a marker of glycolysis and does not specifically accumulate in malignancy. Understanding the physiology and pathophysiology of normal FDG distribution and common incidental findings is therefore essential to the physician interpreting whole-body FDG-PET/CT studies. Whereas many incidental findings are benign and of limited clinical significance, others represent uncommon manifestations of the primary malignancy, second malignancies, or various clinically significant pathologic processes. Patients with a single malignancy are at greater risk of developing synchronous or metachronous second malignancies, possibly related to exposure to shared carcinogenic agents or presence of prooncogenic mutations. The decision of how to pursue an intervention on the basis of an incidental finding is generally left to clinical judgment.

Added value of baseline 18F-FDG uptake in serial 18F-FDG PET for evaluation of response of solid extracerebral tumors to systemic cytotoxic neoadjuvant treatment: a meta-analysis

The purpose of this study was to test the hypothesis that the level of baseline (18)F-FDG uptake in the primary tumor adds value to its relative change in (18)F-FDG uptake in serial PET scans in predicting the histopathologic response to systemic cytotoxic neoadjuvant treatment of patients with solid extracerebral tumors.

METHODS

We performed a literature search from January 1995 through November 2008 using PubMed and Embase. Two reviewers independently selected eligible studies for possible inclusion in the meta-analysis by reviewing titles and abstracts. Inclusion criteria were at least 10 patients, (18)F-FDG PET before and after therapy, (18)F-FDG PET performed with the intention of monitoring the response of solid extracerebral tumors in humans to cytotoxic neoadjuvant systemic therapy, attenuation-corrected (18)F-FDG PET studies, and studies presenting individual patient data (PET results and histopathologic reference test after treatment). Multilevel logistic regression was used to assess the effect of relative change of (18)F-FDG uptake ([baseline - end]/baseline) and baseline (18)F-FDG uptake value with type of tumor and type of treatment as level 1 covariates.

RESULTS

Nineteen studies (all observational; a total of 438 patients [median, 23 patients per study; range, 10-40]) were included, aiming at the accuracy of PET versus histopathology. To quantify PET, maximum standardized uptake value (SUV) was used in 6 studies, mean SUV in 7, SUV (subtype unclear) in 1, tumor-to-background ratio in 3, and dose uptake ratio in 1. The average overall histopathologic response rate was 0.47 (median, 0.50), ranging from 0.17 to 0.88. The relative change in (18)F-FDG uptake was the strongest indicator (P < 0.0001) for tumor response. Baseline (18)F-FDG was not significantly associated as a main factor; however, a significant interaction of baseline uptake and relative change after therapy was observed (P < 0.001).

CONCLUSION

Relative change in (18)F-FDG uptake was the strongest indicator for tumor response, but the level of baseline (18)F-FDG uptake in the primary tumor provided additional information about prediction of response to therapy. These data corroborate and extend the need for standardization, quality assurance, and control of PET studies quantifying (18)F-FDG in oncologic treatment monitoring.

Complementary roles of whole-body diffusion-weighted MRI and 18F-FDG PET: the state of the art and potential applications

(18)F-FDG PET is an established functional imaging modality for the evaluation of human disease. Diffusion-weighted MRI (DWI) is another rapidly evolving functional imaging modality that can be used to evaluate oncologic and nononcologic lesions throughout the body. The information provided by (18)F-FDG PET and DWI can be complementary, because the 2 methods are based on completely different biophysical underpinnings. This article will describe the basic principles, clinical applications, and limitations of DWI. In addition, the available evidence that correlates and compares (18)F-FDG PET and DWI will be reviewed.

The role of choline positron emission tomography/computed tomography in the management of patients with prostate-specific antigen progression after radical treatment of prostate cancer

CONTEXT

Choline positron emission tomography (PET)/computed tomography (CT) is a currently used diagnostic tool in restaging prostate cancer (PCa) patients with increasing prostate-specific antigen (PSA) after either radical prostatectomy (RP) or external-beam radiation therapy (EBRT). However, no final recommendations have been made on the use of this modality for patient management.

OBJECTIVE

To critically analyse the current evidence for the use of choline PET/CT scanning in the management of patients with a progressive increase in PSA after radical treatment for PCa, evaluating its diagnostic accuracy in the detection of recurrences, the clinical predictors of positive PET/CT examinations, and the modalities' role as a guide for tailored therapeutic strategies.

EVIDENCE ACQUISITION

Data on recently published (2003-2010) original articles, review articles, and editorials concerning the role of choline PET/CT in this scenario were analysed.

EVIDENCE SYNTHESIS

The diagnostic accuracy of choline PET in detecting sites of PCa relapse has been investigated by several authors, and the overall reported sensitivity ranges between 38% and 98%. It has been demonstrated that choline PET technology's positive detection rate improves with increasing PSA values. The routine use of choline PET/CT cannot be recommended for PSA values <1 ng/ml. However, in addition to PSA serum value, PSA doubling time (PSA DT), and other clinical and pathologic features-including locally advanced tumour (pT3b-T4) or lymph node involvement at initial staging-should be considered to refer patients to choline PET/CT study. Choline PET/CT may be also proposed as a image guide either for experimental surgical or radiation therapy treatments.

CONCLUSIONS

According to the current available data, choline PET/CT plays a role in the management of biochemical relapse. Its accuracy is correlated to PSA value, PSA DT, and other pathologic features. Choline PET/CT may be proposed as a guide for individualised treatment of recurrence.

Personalized versus evidence-based medicine with PET-based imaging

In this Perspective the feasibility, scope and impact of integrating PET-based personalized medicine into the evidence-based clinical practice of oncology is discussed. The basic concepts of 'evidence-based medicine' and 'personalized medicine' at times seem contradictory; however, I will discuss, with specific clinical situations as examples, a synergistic and probably incremental link between the two and propose that the result of such integration will ultimately improve patient management. Tailoring therapeutic approaches and regimens by molecular imaging, with PET at its forefront, would enable disease management at the individual level and this modification would hopefully further strengthen the evidence-based approach in oncology.

Preliminary clinical applications of a device-dedicated whole-body positron emission tomography reconstruction method: impact on standardized uptake values

BACKGROUND

¹⁸F-fluorodeoxyglucose positron emission tomography has proven relevance in oncological diagnosis, staging and follow-up. The standardized uptake value (SUV) is one of the most widely used semi-quantitative criteria in PET imaging. However, factors such as noise and image resolution affect the measurement of the SUV. We reported earlier that a device-dedicated projector [attenuation-weighted ordered-subsets expectation maximization detector response (AW-OSEM DR), based on point-source measurements] introduces less noise than a geometrical model (AW-OSEM).

OBJECTIVE

The aim of this study was to investigate the AW-OSEM DR method's impact on SUV measurements under clinical conditions.

METHODS

We first performed a bias analysis to assess the accuracy of the quantitation for the two reconstruction methods as a function of target size and the number of iterations, with 14 acquisitions of the NEMA IEC/2001 phantom. We then used each method to calculate the maximum and average SUVs, respectively for 32 lesions.

RESULTS

For all spheres and all iterations, the bias was significantly lower with AW-OSEM DR than with AW-OSEM (P=0.012). Moreover, a paired Student's t-test showed significant intermethod differences for maximum SUV and average SUV (both P<0.001) in cancer patients. Conversely, the two methods did not differ significantly in terms of the mean SUV and signal-to-noise ratio calculated in the liver for each patient (P=0.5 and 0.08, respectively).

CONCLUSION

Phantom and patient studies were performed to quantify the effects of AW-OSEM DR on PET images. The phantom study highlighted the fact that our method produces more accurate images in terms of the SUV, which is an essential quality for ensuring correct diagnosis, follow-up and treatment planning.

Quantitative imaging in oncology patients: Part 2, oncologists' opinions and expectations at major U.S. cancer centers

OBJECTIVE

The purpose of this article is to examine oncologists' opinions and expectations concerning imaging and tumor measurements in patients with cancer.

MATERIALS AND METHODS

An electronic mail survey was sent to 2,400 medical, gynecologic, and radiation oncologists at 55 U.S. National Cancer Institute-funded cancer centers. The survey contained questions about departmental demographics, opinions regarding imaging for patients with cancer, PET/CT utilization, and utilization of the Response Evaluation Criteria in Solid Tumors (RECIST) system in therapy protocols that use imaging as a therapeutic end point.

RESULTS

A total of 492 responses (21%) were received. Sixty percent (294) of respondents were medical oncologists, 9% (45) were gynecologic oncologists, 26% (127) were radiation oncologists, and 5% (25) answered "Other." Ninety-eight percent (431/438) of respondents provide clinical care, and 99% (420/425) have participated in clinical trials. Most respondents (94% [410/438]) expect some or all tumors to be measured at the time of standard initial clinical imaging. Over half (65% [275/426]) think that tumor measurements should be bidimensional. Only 25% (101/400) of respondents' institutions have department rules on the implementation of RECIST measurements. Sixty-eight percent of participants (269/397) think that RECIST is flawed but serviceable. Over half of respondents (56% [221/398]) were not familiar with RECIST 1.1 modifications.

CONCLUSION

Most oncologists at National Cancer Institute-sponsored cancer centers expect tumor measurements to be made in the routine imaging of patients with cancer. Almost two thirds of respondents think that bidimensional measurements of index lesions are satisfactory in routine oncologic imaging. Little consensus exists in the implementation of RECIST measurements for clinical trials at these centers.

The value of (18)F-fluorodeoxyglucose positron emission tomography/computed tomography for staging of primary extranodal head and neck lymphomas

OBJECTIVES/HYPOTHESIS

Using a retrospective approach, the aim of this study was to confirm the previously described value of fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG-PET/CT) in patients with primary extranodal lymphoma of the head and neck region. Additionally, the clinical significance of the semiquantitative analysis of the standardized uptake value (SUV), its predictive role in the follow-up setting, and its value in detection of synchronous primaries were studied.

STUDY DESIGN

Retrospective chart review.

METHODS

Twenty-six patients with a primary extranodal head and neck lymphoma (22 diffuse large B-cell lymphoma, one Hodgkin's lymphoma, three malignant T-cell lymphomas) were included. We retrospectively evaluated the clinical outcomes according to the maximum standardized uptake values of the primary lesion (SUV(max)) and whether a positron emission tomography/computed tomography (PET/CT) was performed or not in the follow-up studies. The median SUV(max) was chosen as the cutoff value. The patients were then grouped as those with either low or high SUV(max), respective to the cutoff value. Event-free survival and cumulative survival were endpoints of interest.

RESULTS

Nineteen patients (73%) were above the age of 60 years; the median age was 70 years (range, 28-87 years). Most primary sites were in the Waldeyer's ring (15 patients, 60%), whereas in four patients (27%) only the palatine tonsil was affected. The SUV(max) ranged from 5.8 to 33.9. In one patient, relevant fluorodeoxyglucose (FDG) uptake within the intestine revealed a cecal adenocarcinoma as a secondary primary. Twenty of the 25 clinically followed patients (80%) achieved complete remission after treatment. Patients with high SUV(max) showed favorable survival (log-rank test, P = .044). A tendency for longer survival within the group with follow-up PET/CT studies could be noted but with no significant statistical difference (P = .349).

CONCLUSIONS

(18)F-FDG-PET/CT imaging is a potent primary staging tool. It also has application as an instrument for evaluation of follow-up and response to therapy in patients suffering from primary extranodal lymphoma and for detection of secondary malignancies. Furthermore, (18)F-FDG uptake by the primary lesion may be related to better survival.

Molecular imaging of breast cancer

Molecular imaging of breast cancer can potentially be used for breast cancer screening, staging, restaging, response evaluation and guiding therapies. Techniques for molecular breast cancer imaging include magnetic resonance imaging (MRI), optical imaging, and radionuclide imaging with positron emission tomography (PET) or single photon emission computed tomography (SPECT). This review focuses on PET and SPECT imaging which can provide sensitive serial non invasive information of tumor characteristics. Most clinical data are gathered on the visualization of general processes such as glucose metabolism with the PET-tracer [(18)F]fluorodeoxyglucose (FDG) and DNA synthesis with [18F]fluoro-L-thymidine (FLT). Increasingly more breast cancer specific targets are imaged such as the estrogen receptor (ER), growth factors and growth factor receptors. Imaging of the ER with the PET tracer 16-alpha-[(18)F]fluoro-17-beta-estradiol (FES) has shown a good correlation between FES tumor uptake and ER density. (111)In-trastuzumab SPECT to image the human epidermal growth factor receptor 2 (HER2) showed that in most patients with metastatic HER2 overexpressing disease more lesions were detected than with conventional staging procedures. The PET tracer (89)Zr-trastuzumab showed excellent, quantifiable, and specific tumor uptake. (111)In-bevacizumab for SPECT and (89)Zr-bevacizumab for PET-imaging have been developed for vascular endothelial growth factor (VEGF) imaging as an angiogenic marker. Lastly, tracers for the receptors EGFR, IGF-1R, PDGF-betaR and the ligand TGFbeta are under development. Although molecular imaging of breast cancer is still not commonly used in daily clinical practice, its application portfolio is expanding rapidly.

Cost-effectiveness analysis of FDG PET-CT in the management of pulmonary metastases from malignant melanoma

OBJECTIVES

Most guidelines consider FDG PET-CT to detect occult extra-pulmonary disease prior to lung metastasectomy. A cost-effectiveness analysis, using a Markov model over a 10 year period, was performed to compare two different surveillance programs, either PET-CT or whole-body CT, in patients with suspected pulmonary metastasised melanoma.

METHODS

Data from published studies provided probabilities for the model. Complication and care costs were obtained from standardised administrative databases from 19 hospitals identified by DRG codes (reported in 2009 Euros). For the cost calculation of PET-CT we performed a microcosting analysis. All costs and benefits were yearly discounted at respectively 3% and 1.5%. Outcomes included life-months gained (LMG) and the number of futile surgeries avoided. Cost-effectiveness ratios were in Euros per LMG. Univariate and probabilistic sensitivity analyses addressed uncertainty in all model parameters.

RESULTS

The PET-CT strategy provided 86.29 LMG (95% CI: 81.50-90.88 LMG) at a discounted cost of euro3,974 (95% CI: euro1,339-12,303), while the conventional strategy provided 86.08 LMG (95% CI: 81.37-90.68 LMG) at a discounted cost of euro5,022 (95% CI: euro1,378-16,018). This PET-CT strategy resulted in a net saving of euro1,048 with a gain of 0.2 LMG. Based on PET-CT findings, 20% of futile surgeries could be avoided.

CONCLUSION

Integrating PET-CT in the management of patients with high risk MM appears to be less costly and more accurate by avoiding futile thoracotomies in one of five patients as well as by providing a small survival benefit at 10 years.

The clinical advances of fluorine-2-D-deoxyglucose--positron emission tomography/computed tomography in urological cancers

Fluorine-18 labeled fluorine-2-D-deoxyglucose (FDG) is the most frequently used positron emission tomography (PET) probe but it has certain limitations when used in urological cancers. The introduction of co-registered PET and computed tomography (PET/CT) represents a major advance in technology and FDG-PET/CT has now become the new standard. The diagnostic performance of FDG-PET and PET/CT depends on the metabolic activity of tumor tissue, which is generally low in primary renal cell and prostate cancers and often in their metastatic deposits. In contrast, both seminomatous and nonseminomatous germ cell tumors are characterized by upregulated glucose metabolism with subsequently increased FDG uptake in tumor sites. Generally, the metabolic activity provides accurate information regarding the presence of a viable tumor, except in patients with residual mature teratoma. Although bladder cancer demonstrates sufficiently increased FDG uptake, primary tumors are difficult to identify due to the renal excretion of FDG. The accuracy of FDG-PET/CT in metabolically active metastases is generally higher compared to conventional CT except for identifying small lung deposits. With disease progression and subsequent de-differentiation of prostate cancer, castrate resistant disease is more likely to present with lesions that have increased glucose metabolism.

18F-FDG PET of locally invasive breast cancer and association of estrogen receptor status with standardized uptake value: microarray and immunohistochemical analysis

PET imaging is useful for evaluating locally advanced primary breast cancer. Expression of specific molecular markers in these cancers, such as estrogen receptor (ER), progesterone receptor (PR), and HER2 status, has direct prognostic and therapeutic implications in patient management. This study aimed to determine whether a relationship exists between tumor glucose use and important molecular markers in invasive breast cancer. For our purposes, tumor glucose use is quantified by the PET-derived parameter maximum standardized uptake value (SUV).

METHODS

Breast tumors from 36 patients were excised and examined histologically after PET. ER, PR, and HER2 status were determined for all lesions histopathologically. In addition, genomewide expression for a subset of 20 tumors was analyzed using the human genome U133A oligonucleotide microarray.

RESULTS

A significant association was found between estrogen ER status and lesion SUV. ER-negative tumors (n = 17; median SUV, 8.5) demonstrated a significantly higher maximum SUV than did ER-positive tumors (n = 19; median SUV, 4.0) (P < 0.001). No significant association existed between SUV and PR status, HER2/neu status, lymph node involvement, or tumor size. Unsupervised hierarchic clustering of the 20 genetically profiled cancers segregated tumor samples into 2 primary groups of 10 patients each, largely corresponding to ER status.

CONCLUSION

In locally invasive primary breast cancer, ER-negative tumors display higher (18)F-FDG uptake than ER-positive tumors. Microarray analysis confirms these data and identifies genes associated with increased glucose use as measured by PET. These genes significantly overlap those of a previously validated ER-status molecular phenotype. These preliminary data support a growing body of evidence that ER-positive and ER-negative breast cancers have distinct disease-specific patterns. Further validation prospectively and with larger numbers will be required to establish a robust molecular signature for metabolic uptake and patterns of aggressive behavior in advanced breast cancer.

PET-CT for response assessment and treatment adaptation in head and neck cancer

Preferred treatment strategies for advanced-stage squamous cell carcinoma of the head and neck have shifted from surgery to organ-preservation approaches such as radiotherapy, which can be combined with chemotherapy or giving of biologically modifying molecules. Preclinical and clinical researchers aim to customise these treatments on the basis of biological tumour characteristics, including tumour cell proliferation, hypoxia, and apoptosis--important resistance mechanisms for cytotoxic antitumour therapy. Monitoring of these biologically relevant variables before and early during treatment could improve patient selection for specific treatment strategies and guide adaptation of treatment at an early stage. PET provides a non-invasive molecular imaging method with the potential ability to undertake repetitive non-invasive quantification of relevant tumour characteristics. We discuss the role of PET scanning and available radiopharmaceutical tracers for treatment selection, early response monitoring, and treatment adaptation in head and neck cancer.

FDG PET and PET/CT: EANM procedure guidelines for tumour PET imaging: version 1.0

The aim of this guideline is to provide a minimum standard for the acquisition and interpretation of PET and PET/CT scans with [18F]-fluorodeoxyglucose (FDG). This guideline will therefore address general information about [18F]-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) and is provided to help the physician and physicist to assist to carrying out, interpret, and document quantitative FDG PET/CT examinations, but will concentrate on the optimisation of diagnostic quality and quantitative information.

FDG PET and PET/CT: EANM procedure guidelines for tumour PET imaging: version 1.0

The aim of this guideline is to provide a minimum standard for the acquisition and interpretation of PET and PET/CT scans with [18F]-fluorodeoxyglucose (FDG). This guideline will therefore address general information about[18F]-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) and is provided to help the physician and physicist to assist to carrying out,interpret, and document quantitative FDG PET/CT examinations,but will concentrate on the optimisation of diagnostic quality and quantitative information.

Economic evaluation of PET and PET/CT in oncology: evidence and methodologic approaches

PET and PET/CT have changed the diagnostic algorithm in oncology. Health care systems worldwide have recently approved reimbursement for PET and PET/CT for staging of non-small cell lung cancer and differential diagnosis of solitary pulmonary nodules because PET and PET/CT have been found to be cost-effective for those uses. Additional indications that are covered by health care systems in the United States and several European countries include staging of gastrointestinal tract cancers, breast cancer, malignant lymphoma, melanoma, and head and neck cancers. Regarding these indications, diagnostic effectiveness and superiority over conventional imaging modalities have been shown, whereas cost-effectiveness has been demonstrated only in part. This article reports on the current knowledge of economic evaluations of PET and PET/CT in oncologic applications. Because more economic evaluations are needed for several clinical indications, we also report on the methodologies for conducting economic evaluations of diagnostic tests and suggest an approach toward the implementation of these tests in future clinical studies.

Innovations in radiotherapy planning of head and neck cancers: role of PET

Modern radiotherapy techniques heavily rely on high-quality medical imaging. PET provides biologic information about the tumor, complementary to anatomic imaging. Integrated PET/CT has found its way into the practice of radiation oncology, and (18)F-FDG PET is being introduced for radiotherapy planning. The functional information possibly augments accurate delineation and treatment of the tumor and its extensions while reducing the dose to surrounding healthy tissues. In addition to (18)F-FDG, other PET tracers are available for imaging specific biologic tumor characteristics determining radiation resistance. For head and neck cancer, the potential gains of PET are increasingly being recognized. This review describes the current role of PET and perspectives on its future use for selection and delineation of radiotherapy target volumes and for biologic characterization of this tumor entity. Furthermore, the potential role of PET for early response monitoring, treatment modification, and patient selection is addressed in this review.

Methodological considerations in quantification of oncological FDG PET studies

Purpose

This review aims to provide insight into the factors that influence quantification of glucose metabolism by FDG PET images in oncology as well as their influence on repeated measures studies (i.e. treatment response assessment), offering improved understanding both for clinical practice and research.

Methods

Structural PubMed searches have been performed for the many factors affecting quantification of glucose metabolism by FDG PET. Review articles and references lists have been used to supplement the search findings.

Results

Biological factors such as fasting blood glucose level, FDG uptake period, FDG distribution and clearance, patient motion (breathing) and patient discomfort (stress) all influence quantification. Acquisition parameters should be adjusted to maximize the signal to noise ratio without exposing the patient to a higher than strictly necessary radiation dose. This is especially challenging in pharmacokinetic analysis, where the temporal resolution is of significant importance. The literature is reviewed on the influence of attenuation correction on parameters for glucose metabolism, the effect of motion, metal artefacts and contrast agents on quantification of CT attenuation-corrected images. Reconstruction settings (analytical versus iterative reconstruction, post-reconstruction filtering and image matrix size) all potentially influence quantification due to artefacts, noise levels and lesion size dependency. Many region of interest definitions are available, but increased complexity does not necessarily result in improved performance. Different methods for the quantification of the tissue of interest can introduce systematic and random inaccuracy.

Conclusions

This review provides an up-to-date overview of the many factors that influence quantification of glucose metabolism by FDG PET.

Assessment of residual tumour by FDG-PET: conventional imaging and clinical examination following primary chemotherapy of large and locally advanced breast cancer

Background:

The aim of this was to evaluate FDG-PET (2-(fluorine-18)-fluoro-2-deoxy-D-glucose positron emission tomography) for assessment of residual tumour after primary chemotherapy of large and locally advanced breast cancer in comparison with conventional imaging modalities.

Methods:

In a prospective multicentre trial, 99 patients underwent one or more breast imaging modalities before surgery in addition to clinical examination, namely, FDG-PET (n=89), mammography (n=47), ultrasound (n=46), and magnetic resonance imaging (MRI) (n=46). The presence of residual tumour by conventional imaging, dichotomised as positive or negative, and the level of FDG uptake (standardised uptake values, SUV) were compared with histopathology, which served as the reference standard. Patients with no residual tumour or only small microscopic foci of residual tumour were classified as having minimal residual disease and those with extensive microscopic and macroscopic residual tumour tissue were classified as having gross residual disease.

Results:

By applying a threshold SUV of 2.0, the sensitivity of FDG-PET for residual tumour was 32.9% (specificity, 87.5%) and increased to 57.5% (specificity, 62.5%) at a threshold SUV of 1.5. Conventional imaging modalities were more sensitive in identifying residual tumour, but had a low corresponding specificity; sensitivity and specificity were as follows: MRI 97.6 and 40.0%, mammography 92.5 and 57.1%, ultrasound 92.0 and 37.5%, respectively. Breast MRI provided the highest accuracy (91.3%), whereas FDG-PET had the lowest accuracy (42.7%).

Conclusions:

FDG-PET does not provide an accurate assessment of residual tumour after primary chemotherapy of breast cancer. Magnetic resonance imaging offers the highest sensitivity, but all imaging modalities have distinct limitations in the assessment of residual tumour tissue when compared with histopathology.

FDG PET/CT in carcinoma of unknown primary

Carcinoma of unknown primary (CUP) is a heterogeneous group of metastatic malignancies in which a primary tumor could not be detected despite thorough diagnostic evaluation. Because of its high sensitivity for the detection of lesions, combined ¹⁸F-fluoro-2-deoxyglucose positron emission tomography (FDG PET)/computed tomography (CT) may be an excellent alternative to CT alone and conventional magnetic resonance imaging in detecting the unknown primary tumor. This article will review the use, diagnostic performance, and utility of FDG PET/CT in CUP and will discuss challenges and future considerations in the diagnostic management of CUP.

Clinical value of 18F-FDG PET/CT in assessing suspicious relapse after rectal cancer resection

AIM: To evaluate the value of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) in the restaging of resected rectal cancer.

METHODS: From January 2007 to Sep 2008, 21 patients who had undergone curative surgery resection for rectal carcinoma with suspicious relapse in conventional imaging or clinical findings were retrospectively enrolled in our study. The patients underwent 28 PET/CT scans (two patients had two scans, one patient had three and one had four scans). Locoregional recurrences and/or distant metastases were confirmed by histological analysis or clinical and imaging follow-up.

RESULTS: Final diagnosis was confirmed by histopathological diagnosis in 12 patients (57.1%) and by clinical and imaging follow-up in nine patients (42.9%). Eight patients had extrapelvic metastases with no evidence of pelvic recurrence. Seven patients had both pelvic recurrence and extrapelvic metastases, and two patients had pelvic recurrence only. ¹⁸F-FDG PET/CT was negative in two patients and positive in 19 patients. ¹⁸F-FDG PET/CT was true positive in 17 patients and false positive in two. The accuracy of ¹⁸F-FDG PET/CT was 90.5%, negative predictive value was 100%, and positive predictive value was 89.5%. Five patients with perirectal recurrence underwent ¹⁸F-FDG PET/CT image guided tissue core biopsy. ¹⁸F-FDG PET/CT also guided surgical resection of pulmonary metastases in three patients and monitored the response to salvage chemotherapy and/or radiotherapy in four patients.

CONCLUSION: ¹⁸F-FDG PET/CT is useful for evaluating suspicious locoregional recurrence and distant metastases in the restaging of rectal cancer after curative resection.

18F-FDG PET/CT for image-guided and intensity-modulated radiotherapy

Advances in technology have allowed extremely precise control of radiation dose delivery and localization within a patient. The ability to confidently delineate target tumor boundaries, however, has lagged behind. (18)F-FDG PET/CT, with its ability to distinguish metabolically active disease from normal tissue, may provide a partial solution to this problem. Here we review the current applications of (18)F-FDG PET/CT in a variety of disease sites, including non-small cell lung cancer, head and neck cancer, and pancreatic adenocarcinoma. This review focuses on the use of (18)F-FDG PET/CT to aid in planning radiotherapy and the associated benefits and challenges. We also briefly consider novel radiopharmaceuticals that are beginning to be used in the context of radiotherapy planning.