Variability of lesion detectability and standardized uptake value according to the acquisition procedure and reconstruction among five PET scanners

Hot spot imaging in cardiovascular diseases: an information statement from SNMMI, ASNC, and EANM

This information statement from the Society of Nuclear Medicine and Molecular Imaging, American Society of Nuclear Cardiology, and European Association of Nuclear Medicine describes the performance, interpretation, and reporting of hot spot imaging in nuclear cardiology. The field of nuclear cardiology has historically focused on cold spot imaging for the interpretation of myocardial ischemia and infarction. Hot spot imaging has been an important part of nuclear medicine, particularly for oncology or infection indications, and the use of hot spot imaging in nuclear cardiology continues to expand. This document focuses on image acquisition and processing, methods of quantification, indications, protocols, and reporting of hot spot imaging. Indications discussed include myocardial viability, myocardial inflammation, device or valve infection, large vessel vasculitis, valve calcification and vulnerable plaques, and cardiac amyloidosis. This document contextualizes the foundations of image quantification and highlights reporting in each indication for the cardiac nuclear imager.

Understanding the importance of quality control and quality assurance in preclinical PET/CT imaging

The fundamental principle of experimental design is to ensure efficiency and efficacy of the performed experiments. Therefore, it behoves the researcher to gain knowledge of the technological equipment to be used. This should include an understanding of the instrument quality control and assurance requirements to avoid inadequate or spurious results due to instrumentation bias whilst improving reproducibility. Here, the important role of preclinical positron emission tomography/computed tomography and the scanner's required quality control and assurance is presented along with the suggested guidelines for quality control and assurance. There are a multitude of factors impeding the continuity and reproducibility of preclinical research data within a single laboratory as well as across laboratories. A more robust experimental design incorporating validation or accreditation of the scanner performance can reduce inconsistencies. Moreover, the well-being and welfare of the laboratory animals being imaged is prime justification for refining experimental designs to include verification of instrumentation quality control and assurance. Suboptimal scanner performance is not consistent with the 3R principle (Replacement, Reduction, and Refinement) and potentially subjects animals to unnecessary harm. Thus, quality assurance and control should be of paramount interest to any scientist conducting animal studies. For this reason, through this work, we intend to raise the awareness of researchers using PET/CT regarding quality control/quality assurance (QC/QA) guidelines and instil the importance of confirming that these are routinely followed. We introduce a basic understanding of the PET/CT scanner, present the purpose of QC/QA as well as provide evidence of imaging data biases caused by lack of QC/QA. This is shown through a review of the literature, QC/QA accepted standard protocols and our research. We also want to encourage researchers to have discussions with the PET/CT facilities manager and/or technicians to develop the optimal designed PET/CT experiment for obtaining their scientific objective. Additionally, this work provides an easy gateway to multiple resources not only for PET/CT knowledge but for guidelines and assistance in preclinical experimental design to enhance scientific integrity of the data and ensure animal welfare.

The predictive value of total-body PET/CT in non-small cell lung cancer for the PD-L1 high expression

Purpose

Total-body positron emission tomography/computed tomography (PET/CT) provides faster scanning speed, higher image quality, and lower injected dose. To compensate for the shortcomings of the maximum standard uptake value (SUVmax), we aimed to normalize the values of PET parameters using liver and blood pool SUV (SUR-L and SUR-BP) to predict programmed cell death-ligand 1 (PD-L1) expression in non-small cell lung cancer (NSCLC) patients.

Materials and methods

A total of 138 (104 adenocarcinoma and 34 squamous cell carcinoma) primary diagnosed NSCLC patients who underwent ¹⁸F-FDG-PET/CT imaging were analyzed retrospectively. Immunohistochemistry (IHC) analysis was performed for PD-L1 expression on tumor cells and tumor-infiltrating immune cells with 22C3 antibody. Positive PD-L1 expression was defined as tumor cells no less than 50% or tumor-infiltrating immune cells no less than 10%. The relationships between PD-L1 expression and PET parameters (SUVmax, SUR-L, and SUR-BP) and clinical variables were analyzed. Statistical analysis included χ² test, receiver operating characteristic (ROC), and binary logistic regression.

Results

There were 36 patients (26%) expressing PD-L1 positively. Gender, smoking history, Ki-67, and histologic subtype were related factors. SUVmax, SUR-L, and SUR-BP were significantly higher in the positive subset than those in the negative subset. Among them, the area under the curve (AUC) of SUR-L on the ROC curve was the biggest one. In NSCLC patients, the best cutoff value of SUR-L for PD-L1-positive expression was 4.84 (AUC = 0.702, P = 0.000, sensitivity = 83.3%, specificity = 54.9%). Multivariate analysis confirmed that age and SUR-L were correlated factors in adenocarcinoma (ADC) patients.

Conclusion

SUVmax, SUR-L, and SUR-BP had utility in predicting PD-L1 high expression, and SUR-L was the most reliable parameter. PET/CT can offer reference to screen patients for first-line atezolizumab therapy.

Quantitative SPECT/CT for dosimetry of peptide receptor radionuclide therapy

Neuroendocrine tumors (NETs) are uncommon malignancies of increasing incidence and prevalence. As these slow growing tumors usually overexpress somatostatin receptors (SSTRs), the use of ⁶⁸Ga-DOTA-peptides (gallium-68 chelated with dodecane tetra-acetic acid to somatostatin), which bind to the SSTRs, allows for PET based imaging and selection of patients for peptide receptor radionuclide therapy (PRRT). PRRT with radiolabeled somatostatin analogues such as ¹⁷⁷Lu-DOTATATE (lutetium-177-[DOTA,Tyr³]-octreotate), is mainly used for the treatment of metastatic or inoperable NETs. However, PRRT is generally administered at a fixed injected activity in order not to exceed dose limits in critical organs, which is suboptimal given the variability in radiopharmaceutical uptake among patients. Advances in SPECT (single photon emission computed tomography) imaging enable the absolute quantitative measure of the true radiopharmaceutical distribution providing for PRRT dosimetry in each patient. Personalized PRRT based on patient-specific dosimetry could improve therapeutic efficacy by optimizing effective tumor absorbed dose while limiting treatment related radiotoxicity.

Prognostic value of pretreatment tumor-to-blood standardized uptake ratio (SUR) in rectal cancer

OBJECTIVES

The prognostic value of SUV on pretreatment F-18 FDG PET/CT imaging in patients with rectal cancer is a matter of debate. SUR is of prognostic value for survival in different cancers. In this study, we aimed to examine the potential prognostic value of SUR and other parameters in pretreatment F-18 FDG PET/CT for non-metastatic rectal cancer.

METHODS

One hundred four non-metastatic rectal cancer patients who underwent pretreatment PET/CT between March 2012 and January 2018 were included in the study. Firstly, SUV_max, SUV_mean, MTV, and TLG were calculated semi-automatically at the workstation. SUR was calculated as the ratio of tumor SUV_max to thoracic aorta blood SUV_mean. Univariate Cox regression and Kaplan-Meier analysis were used to evaluate overall survival (OS), progression free survival (PFS), and local recurrence (LR). Then, multivariate Cox regression analysis, which included the parameters that were significant in the univariate analysis, was performed.

RESULTS

Multivariate Cox regression analysis revealed that SUR was a prognostic factor for PFS. Age and T stage were prognostic factors for both OS and PFS. MTV was found to be independent risk factors for OS.

CONCLUSIONS

In our study, SUR was the only F-18 FDG PET/CT parameter found to be significant for PFS. The development of new parameters can increase the prognostic value of F-18 FDG PET/CT.

Absolute radiotracer concentration measurement using whole-body solid-state SPECT/CT technology: in vivo/in vitro validation

The accuracy of recently approved quantitative clinical software was determined by comparing in vivo/in vitro measurements for a solid-state cadmium-zinc-telluride SPECT/CT (single photon emission computed tomography/x-ray computed tomography) camera. Bone SPECT/CT, including the pelvic region in the field of view, was performed on 16 patients using technetium-99m methylene diphosphonic acid as a radiotracer. After imaging, urine samples from each patient provided for the measurement of in vitro radiopharmaceutical concentrations. From the SPECT/CT images, three users measured in vivo radiotracer concentration and standardized uptake value (SUV) for the bladder using quantitative software (Q.Metrix, GE Healthcare). Linear regression was used to validate any in vivo/in vitro identity relations (ideally slope = 1, intercept = 0), within a 95% confidence interval (CI). Thirteen in vivo/in vitro pairs were available for further analysis, after rejecting two as clinically irrelevant (SUVs > 100 g/mL) and one as an outlier (via Cook's distance calculations). All linear regressions (R² ≥ 0.85, P < 0.0001) provided identity in vivo/in vitro relations (95% CI), with SUV averages from all users giving a slope of 0.99 ± 0.25 and intercept of 0.14 ± 5.15 g/mL. The average in vivo/in vitro residual difference was < 20%. Solid-state SPECT/CT imaging can reliably provide in vivo urinary bladder radiotracer concentrations within approximately 20% accuracy. This practical, non-invasive, in vivo quantitation method can potentially improve diagnosis and assessment of response to treatment. Graphical abstract.

Use of a Qualification Phantom for PET Brain Imaging in a Multicenter Consortium: A Collaboration Between the Pediatric Brain Tumor Consortium and the SNMMI Clinical Trials Network

The purpose of this study was to assess image quality and quantitative brain PET across a multicenter consortium. Methods: All academic centers and children's hospitals in the Pediatric Brain Tumor Consortium (PBTC) scanned a phantom developed by the Society of Nuclear Medicine and Molecular Imaging Clinical Trials Network (SNMMI CTN) for the validation of brain PET studies associated with clinical trials. The phantom comprises 2 separate, fillable sections: a resolution/uniformity section and a clinical simulation section. The resolution/uniformity section is a cylinder 12.7 cm long and 20 cm in diameter; spatial resolution is evaluated subjectively with 2 sets of rods (hot and cold) of varying diameter (4.0, 5.0, 6.25, 7.81, 9.67, and 12.2 mm) and spacing (twice the rod diameter). The clinical simulation section simulates a transverse section of midbrain with ventricles and gray and white matter compartments. If properly filled, hot rods have a 4:1 target-to-background ratio, and gray-to-white matter sections have a 4:1 ratio. Uniformity and image quality were evaluated using the SUV in a small volume of interest as well as subjectively by 2 independent observers using a 4-point scale. Results: Eleven PBTC sites scanned the phantom on 13 PET scanners. The phantom's complexity led to suboptimal filling, particularly of the hot rod section, in 5 sites. The SUV in the uniformity section was within 10% of unity on only 5 of 13 scanners, although 12 of 13 were subjectively judged to have very good to excellent uniformity. Four of 6 hot rods were discernable by all 13 scanners, whereas 3 of 6 cold rods were discernable by only 5 scanners. Four of 13 scanners had a gray-to-white matter ratio between 3.0 and 5.0 (4.0 is truth); however, 11 of 13 scanners were subjectively judged to have very good or excellent image quality. Conclusion: Eleven sites were able to image a powerful phantom developed by the SNMMI CTN that evaluated image uniformity, spatial resolution, and image quality of brain PET. There was considerable variation in PET data across the PBTC sites, possibly resulting from variations in scanning across the sites due to challenges in filling the phantom.

Multicentre analysis of PET SUV using vendor-neutral software: the Japanese Harmonization Technology (J-Hart) study

Background

Recent developments in hardware and software for PET technologies have resulted in wide variations in basic performance. Multicentre studies require a standard imaging protocol and SUV harmonization to reduce inter- and intra-scanner variability in the SUV. The Japanese standardised uptake value (SUV) Harmonization Technology (J-Hart) study aimed to determine the applicability of vendor-neutral software on the SUV derived from positron emission tomography (PET) images. The effects of SUV harmonization were evaluated based on the reproducibility of several scanners and the repeatability of an individual scanner.

Images were acquired from 12 PET scanners at nine institutions. PET images were acquired over a period of 30 min from a National Electrical Manufacturers Association (NEMA) International Electrotechnical Commission (IEC) body phantom containing six spheres of different diameters and an ¹⁸F solution with a background activity of 2.65 kBq/mL and a sphere-to-background ratio of 4. The images were reconstructed to determine parameters for harmonization and to evaluate reproducibility. PET images with 2-min acquisition × 15 contiguous frames were reconstructed to evaluate repeatability. Various Gaussian filters (GFs) with full-width at half maximum (FWHM) values ranging from 1 to 15 mm in 1-mm increments were also applied using vendor-neutral software. The SUV_max of spheres was compared with the reference range proposed by the Japanese Society of Nuclear Medicine (JSNM) and the digital reference object (DRO) of the NEMA phantom. The coefficient of variation (CV) of the SUV_max determined using 12 PET scanners (CV_repro) was measured to evaluate reproducibility. The CV of the SUV_max determined from 15 frames (CV_repeat) per PET scanner was measured to determine repeatability.

Results

Three PET scanners did not require an additional GF for harmonization, whereas the other nine required additional FWHM values of GF ranging from 5 to 9 mm. The pre- and post-harmonization CV_repro of six spheres were (means ± SD) 9.45% ± 4.69% (range, 3.83–15.3%) and 6.05% ± 3.61% (range, 2.30–10.7%), respectively. Harmonization significantly improved reproducibility of PET SUV_max (P = 0.0055). The pre- and post-harmonization CV_repeat of nine scanners were (means ± SD) 6.59% ± 1.29% (range, 5.00–8.98%) and 4.88% ± 1.64% (range, 2.65–6.72%), respectively. Harmonization also significantly improved the repeatability of PET SUV_max (P < 0.0001).

Conclusions

Harmonizing SUV using vendor-neutral software produced SUV_max for 12 scanners that fell within the JSNM reference range of a NEMA body phantom and improved SUV_max reproducibility and repeatability.

Metabolic Tumor Volume Metrics in Lymphoma

Although visual assessment using the Deauville criteria is strongly recommended by guidelines for treatment response monitoring in all FDG-avid lymphoma histologies, the high rate of false-positives and concerns about interobserver variability have motivated the development of quantitative tools to facilitate objective measurement of tumor response in both routine and clinical trial settings. Imaging studies using functional quantitative measures play a significant role in profiling oncologic processes. These quantitative metrics allow for objective end points in multicenter clinical trials. However, the standardization of imaging procedures including image acquisition parameters, reconstruction and analytic measures, and validation of these methods are essential to enable an individualized treatment approach. A robust quality control program associated with the inclusion of proper scanner calibration, cross-calibration with dose calibrators and across other scanners is required for accurate quantitative measurements. In this section, we will review the technical and methodological considerations related to PET-derived quantitative metrics and the relevant published data to emphasize the potential value of these metrics in the prediction of patient prognosis in lymphoma.

Prognostic Value of Tumor-to-Blood Standardized Uptake Ratio in Patients with Resectable Non-Small-Cell Lung Cancer

OBJECTIVES

Previously published studies showed that the standard tumor-to-blood standardized uptake value (SUV) ratio (SUR) was a more accurate prognostic method than tumor maximum standardized uptake value (SUV_max). This study evaluated and compared prognostic value of positron emission tomography (PET) parameters and normalized value of PET parameters by blood pool SUV in non-small-cell lung cancer (NSCLC) patients who received curative surgery.

METHODS

Seventy-seven patients who underwent curative resection for NSCLC between January 2010 to December 2013 were enrolled in this study. ¹⁸Fluorine-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) was performed before surgery. The mean standardized uptake value (SUV_mean), SUV_max, metabolic tumor volume (MTV), and total lesion glycolysis (TLG) of each lesion was measured, on the workstation. SUR_mean, SUR_max, and TLGSUR were calculated by dividing each of them by descending aorta SUV_mean. Cox proportional hazards regression was used to analyze the effect of age, sex, pathological parameters, and PET parameters on recurrence and death.

RESULTS

In Cox regression analysis, N stage predicted for both recurrence (p < 0.0001) and death (p < 0.0001). SUR_max predicted recurrence (p = 0.0014), not death. Area under the receiver operating characteristic curve of SUR_max was 0.759 with cutoff value 4.004. However, SUV_max, SUV_mean, MTV, TLG, SUR_mean, and TLGSUR predicted neither recurrence nor death.

CONCLUSIONS

Among PET parameters, SUR_max was the independent predictor of recurrence in NSCLC patients who received curative surgery. N stage was the independent prognostic factor for both recurrence and death. Both parameters could be used to stratify the risk of NSCLC patients.

Combining standardized uptake value of FDG-PET and apparent diffusion coefficient of DW-MRI improves risk stratification in head and neck squamous cell carcinoma

OBJECTIVES

To assess the independent prognostic value of standardized uptake value (SUV) and apparent diffusion coefficient (ADC), separately and combined, in order to evaluate if the combination of these two variables allows further prognostic stratification of patients with head and neck squamous cell carcinomas (HNSCC).

METHODS

Pretreatment SUV and ADC were calculated in 57 patients with HNSCC. Mean follow-up was 21.3 months. Semiquantitative analysis of primary tumours was performed using SUV_maxT/B, ADC_mean, ADC_min and ADC_max. The prognostic value of SUV_maxT/B, ADC_mean, ADC_min and ADC_max in predicting disease-free survival (DFS) was evaluated with log-rank test and Cox regression models.

RESULTS

Patients with SUV_maxT/B ≥5.75 had an overall worse prognosis (p = 0.003). After adjusting for lymph node status and diameter, SUV_maxT/B and ADC_min were both significant predictors of DFS with hazard ratio (HR) = 10.37 (95 % CI 1.22-87.95) and 3.26 (95 % CI 1.20-8.85) for SUV_maxT/B ≥5.75 and ADC_min ≥0.58 × 10^-3 mm²/s, respectively. When the analysis was restricted to subjects with SUV_maxT/B ≥5.75, high ADC_min significantly predicted a worse prognosis, with adjusted HR = 3.11 (95 % CI 1.13-8.55).

CONCLUSIONS

The combination of SUV_maxT/B and ADC_min improves the prognostic role of the two separate parameters; patients with high SUV_maxT/B and high ADC_min are associated with a poor prognosis.

KEY POINTS

• High SUV _maxT/B is a poor prognostic factor in HNSCC • High ADC _min is a poor prognostic factor in HNSCC • In patients with high SUV _maxT/B , high ADC _min identified those with worse prognosis.

Quantitative Imaging in Radiation Oncology: An Emerging Science and Clinical Service

Radiation oncology has long required quantitative imaging approaches for the safe and effective delivery of radiation therapy. The past 10 years has seen a remarkable expansion in the variety of novel imaging signals and analyses that are starting to contribute to the prescription and design of the radiation treatment plan. These include a rapid increase in the use of magnetic resonance imaging, development of contrast-enhanced imaging techniques, integration of fluorinated deoxyglucose-positron emission tomography, evaluation of hypoxia imaging techniques, and numerous others. These are reviewed with an effort to highlight challenges related to quantification and reproducibility. In addition, several of the emerging applications of these imaging approaches are also highlighted. Finally, the growing community of support for establishing quantitative imaging approaches as we move toward clinical evaluation is summarized and the need for a clinical service in support of the clinical science and delivery of care is proposed.

Role of PET quantitation in the monitoring of cancer response to treatment: Review of approaches and human clinical trials

Positron emission tomography (PET) measures of cancer metabolism and cellular proliferation are increasingly being studied as markers of cancer response to treatment, with the goal of using them as predictors of patient therapeutic outcomes - i.e., as surrogate outcome measures. The primary PET radiotracers thus far used for monitoring response of cancer to treatment are ¹⁸F-fluorodeoxyglucose (FDG) for studying abnormal energy metabolism and ¹⁸F-fluorothymidine (FLT) for examining cell proliferation. Both FDG and FLT PET quantitation of cancer response to treatment have been found to correlate with patient outcomes, mostly in single-center studies. The aim of this review is to summarize the impact of commonly selected PET quantitation methods on the ability of PET measures to quantitate cancer response to treatment. An understanding of the biochemistry and kinetics of FDG and FLT uptake and knowledge of the expected tracer uptake by cancerous processes relative to background uptake are required to select appropriate PET quantitation methods for trials testing for correlations between PET measures and patient outcome. PET measures may eventually serve as predictive biomarkers capable of guiding individualized treatment and improving patient outcomes and quality of life by early identification of ineffective therapies. PET can also potentially identify patients who would be good candidates for molecularly targeted drugs and monitor response to these personalized therapies.

Evaluation of PET quantification accuracy in vivo. Comparison of measured FDG concentration in the bladder with urine samples

Quantitative positron emission tomography (PET) requires accurate scanner calibration, which is commonly performed using phantoms. It is not clear to what extent this procedure ensures quantitatively correct results in vivo, since certain conditions differ between phantom and patient scans.

AIM

We, therefore, have evaluated the actual quantification accuracy in vivo of PET under clinical routine conditions.

PATIENTS, METHODS

We determined the activity concentration in the bladder in patients undergoing routine [18F]FDG whole body investigations with three different PET scanners (Siemens ECAT EXACT HR+ PET: n = 21; Siemens Biograph 16 PET/CT: n = 16; Philips Gemini-TF PET/CT: n = 19). Urine samples were collected immediately after scan. Activity concentration in the samples was determined in well counters cross-calibrated against the respective scanner. The PET (bladder) to well counter (urine sample) activity concentration ratio was determined.

RESULTS

Activity concentration in the bladder (PET) was systematically lower than in the urine samples (well counter). The patient-averaged PET to well counter ratios for the investigated scanners are (mean ± SEM): 0.881 ± 0.015 (ECAT HR+), 0.898 ± 0.024 (Biograph 16), 0.932 ± 0.024 (Gemini-TF). These values correspond to underestimates by PET of 11.9%, 10.2%, and 6.8%, respectively.

CONCLUSIONS

The investigated PET systems consistently underestimate activity concentration in the bladder. The comparison of urine samples with PET scans of the bladder is a straightforward means for in vivo evaluation of the expectable quantification accuracy. The method might be interesting for multi-center trials, for additional quality assurance in PET and for investigation of PET/MR systems for which clear proof of sufficient quantitative accuracy in vivo is still missing.

FDG-PET imaging in mild traumatic brain injury: a critical review

Traumatic brain injury (TBI) affects an estimated 1.7 million people in the United States and is a contributing factor to one third of all injury related deaths annually. According to the CDC, approximately 75% of all reported TBIs are concussions or considered mild in form, although the number of unreported mild TBIs (mTBI) and patients not seeking medical attention is unknown. Currently, classification of mTBI or concussion is a clinical assessment since diagnostic imaging is typically inconclusive due to subtle, obscure, or absent changes in anatomical or physiological parameters measured using standard magnetic resonance (MR) or computed tomography (CT) imaging protocols. Molecular imaging techniques that examine functional processes within the brain, such as measurement of glucose uptake and metabolism using [¹⁸F]fluorodeoxyglucose and positron emission tomography (FDG-PET), have the ability to detect changes after mTBI. Recent technological improvements in the resolution of PET systems, the integration of PET with magnetic resonance imaging (MRI), and the availability of normal healthy human databases and commercial image analysis software contribute to the growing use of molecular imaging in basic science research and advances in clinical imaging. This review will discuss the technological considerations and limitations of FDG-PET, including differentiation between glucose uptake and glucose metabolism and the significance of these measurements. In addition, the current state of FDG-PET imaging in assessing mTBI in clinical and preclinical research will be considered. Finally, this review will provide insight into potential critical data elements and recommended standardization to improve the application of FDG-PET to mTBI research and clinical practice.

Multivariate analysis of various factors affecting background liver and mediastinal standardized uptake values

Purpose of the Study:

Standardized uptake value (SUV) is the most commonly used semi-quantitative PET parameter. Various response assessment criteria grade the tumor uptake relative to liver or mediastinal uptake. However various factors can affect the background SUV values. This prospective study was carried out to assess the variability of liver and mediastinal SUVs normalized to lean body mass (SUL-L, SUL-M), body surface area (SUB-L, SUB-M), and body weight (SUW-L, SUW-M) and their dependence on various factors which can affect SUV values.

Materials and Methods:

Eighty-eight patients who underwent F-18 FDG PET/CT for various oncological indications were prospectively included in this study. SUVs of liver and mediastinum were calculated by ROIs drawn as suggested by Wahl, et al., in PERCIST 1.0 criteria. Multivariate linear regression analysis was done to assess for the various factors influencing the SUVs of liver and mediastinum. Factors assessed were age, sex, weight, blood glucose level, diabetic status, and uptake period. A P value less than 0.01 was considered significant.

Results:

SUL-L, SUL-M, SUB-L, SUB-M, SUW-L, SUW-M were not affected significantly by age, sex, blood glucose levels, diabetic status. The uptake period had a statistically significant effect on SUL-L (P = 0.007) and SUW-L (P = 0.008) with a progressive decrease with increasing uptake time. Body weight showed a statistically significant effect on SUW-L (P = 0.001) while SUL-L and SUB-L were not dependent on weight. SUB-L was least dependent on weight (P = 0.851) when compared with SUL-L (P = 0.425). However SUL-L was also not affected statistically significantly by variations in body weight (P = 0.425). Mediastinal SUVs were not significantly affected by any of the factors.

Conclusions:

As mediastinal SUVs are not affected significantly by any of the factors, it can be considered as background when wide variations occur in uptake times or weight of the patient when comparing two PET/CT studies to evaluate response.

Early experiences in establishing a regional quantitative imaging network for PET/CT clinical trials

The Seattle Cancer Care Alliance (SCCA) is a Pacific Northwest regional network that enables patients from community cancer centers to participate in multicenter oncology clinical trials where patients can receive some trial-related procedures at their local center. Results of positron emission tomography (PET) scans performed at community cancer centers are not currently used in SCCA Network trials since clinical trials customarily accept results from only trial-accredited PET imaging centers located at academic and large hospitals. Oncologists would prefer the option of using standard clinical PET scans from Network sites in multicenter clinical trials to increase accrual of patients for whom additional travel requirements for imaging are a barrier to recruitment. In an effort to increase accrual of rural and other underserved populations to Network trials, researchers and clinicians at the University of Washington, SCCA and its Network are assessing the feasibility of using PET scans from all Network sites in their oncology clinical trials. A feasibility study is required because the reproducibility of multicenter PET measurements ranges from approximately 3% to 40% at national academic centers. Early experiences from both national and local PET phantom imaging trials are discussed, and next steps are proposed for including patient PET scans from the emerging regional quantitative imaging network in clinical trials. There are feasible methods to determine and characterize PET quantitation errors and improve data quality by either prospective scanner calibration or retrospective post hoc corrections. These methods should be developed and implemented in multicenter clinical trials employing quantitative PET imaging of patients.

Design considerations for using PET as a response measure in single site and multicenter clinical trials

RATIONALE AND OBJECTIVES

Positron emission tomography (PET) is used to evaluate response to therapy with increasing interest in having PET provide endpoints for clinical trials. Here we demonstrate impacts of PET measurement error and choice of quantification method on clinical trial design.

MATERIALS AND METHODS

Sample size was calculated for two-arm randomized trials with percent change in (18)F-fluorodeoxyglucose (FDG) PET uptake as an efficacy endpoint. Two methods of uptake quantification were considered: standardized uptake values (SUVs) and kinetic measures from dynamic imaging. Calculations assumed a 20 percentage point difference in treatment groups' average percent change, and yielded 80% power at α = 0.05. The range of precision (10%-40%) in PET uptake measures was based on review of the literature. The range of SUV sensitivities (50%-100%) relative to kinetic analyses was based on a study of 75 locally advanced breast cancer patients.

RESULTS

Sample sizes increased from 8 to 126 as PET precision worsened from 10% to 40% at full measurement sensitivity to true change. In a subgroup with low initial FDG uptake, a sample size of 126 was required under 20% standard deviation using clinical SUVs. More sophisticated imaging quantification could reduce this sample size to 32.

CONCLUSIONS

The dependence of sample size on measurement precision and the sensitivity of imaging measures to true change should be considered in single site and multicenter PET trials to avoid underpowered studies with inconclusive results. Sophisticated PET imaging methods that are more sensitive to changes in uptake may be advantageous in early studies with limited patient numbers.

Best practices: consensus on performing positron emission tomography-computed tomography for radiation therapy planning and for therapy response assessment

The incorporation of positron emission tomography-computed tomography (PET-CT) into oncological imaging has expanded rapidly since the hybrid scanners were introduced approximately 10 years ago. PET-CT is becoming the standard of practice for the imaging diagnosis and staging of most cancers. Since its introduction, hardware-registered PET and CT images produced by a PET-CT scan were recognized as valuable not only for detection, staging and restaging applications but also for optimizing radiation treatment planning. Even before the introduction of PET-CT, the value of metabolic imaging with the use of FDG PET was recognized as a potentially powerful means of assessing response to various therapies, particularly chemotherapy regimens. To better understand the optimal use of PET-CT in radiation therapy planning and the role of PET-CT in assessing response to therapy, we invited experts from various disciplines to participate in focus group meetings that took place in 2009 and 2010. The Symposia focused on the use of PET-CT imaging in radiation therapy planning (2009) and the use of PET-CT in therapy response assessment (2010). This article will summarize areas of consensus reached by the group regarding many of the discussion topics. The consensus summaries covered in this article are meant to provide direction for future discussions on how to improve the application of this hybrid modality to optimize patient care.

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.

Variability in PET quantitation within a multicenter consortium

PURPOSE

The purpose of this study was to evaluate the variability in quantitation of positron emission tomography (PET) data acquired within the context of a multicenter consortium.

METHODS

PET quantitation phantoms designed by American Association of Physicists in Medicine/ Society of Nuclear Medicine Task Group 145 were sent to the ten member sites of the Pediatric Brain Tumor Consortium (PBTC), a NIH-funded research consortium investigating the biology and therapies for brain tumors in children. The phantoms were water-filled cylinders (18.6 cm inside height and 20.4 cm inside diameter) based on the standard ACR phantom with four small, "hot" cylinders of varying diameters (8, 12, 16, 25 mm, all with 38 mm height), consisting of an equilibrium mixture of 68Ge/68Ga in an epoxy matrix. At each site, the operator added the appropriate amount of 18F to the water in the background in order to attain a feature-to-background ratio of roughly 4:1. The phantom was imaged and reconstructed as if it were a brain PET scan for the PBTC. An approximately 12 mm circular region of interest (ROI) was placed over each feature and in a central area in the background. The mean and maximum pixel values for each ROI were requested from local sites in units of activity concentration (Bq/ml) and the standard uptake value (SUV) (g/mL) based on bodyweight. The activity concentration was normalized by the decay-corrected known activity concentration for the features, and reported as the absolute recovery coefficient (RC). In addition, central analyses were performed by two observers

RESULTS

The ten sites successfully imaged the phantom within 5 months and submitted the quantitative results and the phantom image data to the PBTC Operations and Biostatistics Center. The local site-based and central analyses yielded similar mean values for RC. Local site-based SUV measurements of the hot cylindrical features yielded greater variability than central analysis (COV range of 29.9%-42.8% compared to 7.7%-23.2%). Correcting for miscalculations in the local site reported SUVs substantially reduced the variation to levels similar to the central analysis (COV range of 8.8%-18.4%) and also led to the local sites providing a similar mean of the SUV values to those from the central analysis. In the central analysis, the use of mean SUV in place of maximum SUV for an ROI of fixed size substantially reduced the variation in the SUV values (COV ranges of 7.7%-11.3% vs. 9.3%-23.2%).

CONCLUSIONS

Based on this investigation, a SUV variability in the range of 10%-25% due solely to instrument and analysis factors can be expected in the context of a multicenter consortium if a central reading is used and quality assurance and quality control procedures are followed. The overall SUV variability can be expected to be larger than this due to biological and protocol factors.

Standards for PET image acquisition and quantitative data analysis

Quantitative (18)F-FDG PET is increasingly being recognized as an important tool for diagnosis, determination of prognosis, and response monitoring in oncology. However, PET quantification with, for example, standardized uptake values (SUVs) is affected by many technical and physiologic factors. As a result, some of the variations in the literature on SUV-based patient outcomes are explained by differences in (18)F-FDG PET study methods. Various technical and clinical studies have been performed to understand the factors affecting PET quantification. On the basis of the results of those studies, several recommendations and guidelines have been proposed with the aims of improving the image quality and the quantitative accuracy of (18)F-FDG PET studies. In this contribution, an overview of recommendations and guidelines for quantitative (18)F-FDG PET studies in oncology is provided. Special attention is given to the rationale underlying certain recommendations and to some of the differences in various guidelines.