The 68 Ge phantom-based FDG-PET site qualification program for clinical trials adopted by FIL (Italian Foundation on Lymphoma)

Total Metabolic Tumor Volume Is a Strong Independent Prognostic Factor in Follicular Lymphomas: Results From a Sub-Study of the FOLL12 Trial

Discordant results have been generated regarding the prognostic role of Total Metabolic Tumor Volume (TMTV) in Follicular Lymphoma (FL). The use of prospective data and the adoption of the newly defined standardized SUV4 method for calculating TMTV may generate stronger evidence. We conducted a pre-planned post hoc analysis of the prospective multicenter randomized phase III FOLL12 trial for newly diagnosed high tumor burden FL (grade 1-3a), which mandated baseline staging with PET. Baseline PET/CT scans were reviewed centrally, and TMTV was calculated using the fixed threshold of SUV4. Kaplan-Meier and Cox regression were used for survival analysis. The primary study endpoint was Progression free Survival (PFS). A total of 689 FL patients were available for TMTV definition. Median TMTV was 161 mL (IQR 50 to 388 mL) and the best cutoff value was set at 180 mL. Patients with high TMTV had a significantly lower 5-year PFS compared to those with low TMTV: 59% (95% CI, 53-65%) vs. 74% (95% CI, 69-78%) HR 1.61 (95% CI, 1.24-2.09). Prognostic role of TMTV was independent of study arm, chemotherapy regimen, and FLIPI2. Combined with FLIPI-2, we identified three groups with different 5-yr PFS rates, with the lowest rates (51%) for patients with high TMTV and high FLIPI2. Combined TMTV and FLIPI model was also prognostic to predict the risk of early progression and of death. Applying the SUV4 standard method pre-treatment TMTV is confirmed as a strong and independent predictor of PFS in FL patients. Integrating TMTV with FLIPI-2 improves risk assessment.

Evaluating long-term performance and quality control of the uMI 550 positron emission tomography- computed tomography (PET-CT) system: A comprehensive scientific analysis

INTRODUCTION

Ensuring the long-term performance and reliability of positron emission tomography-computed tomography (PET-CT) systems is essential for accurate clinical diagnostics and treatment planning. This study provides a comprehensive analysis of the periodic quality control (QC) processes of the uMI 550 PET-CT system, focusing on key performance parameters such as standardized uptake value (SUV) accuracy, spatial alignment, and image uniformity.

METHODS

Periodic semi-annual QC tests were conducted to evaluate the system's performance across multiple parameters. Key metrics included SUV measurements, spatial alignment across X, Y, and Z axes, and uniformity tests. Statistical analyses assessed variability and stability over time, including ANOVA, t-tests, and linear regression.

RESULTS

The results demonstrated consistent SUV measurements within the reference range of 0.95-1.05, indicating robust quantitative accuracy. Spatial alignment was maintained within a tolerance of -1.5 mm to +1.5 mm, ensuring geometric integrity crucial for accurate image fusion in radiotherapy planning. Uniformity tests showed transverse and axial uniformity values remained within acceptable limits (0.00-0.05), ensuring high-quality imaging across the field of view. Statistical analyses confirmed no significant drift or variability across QC intervals, highlighting the system's reliability over time.

CONCLUSION

The uMI 550 PET-CT system demonstrated consistent performance across critical parameters, validating its suitability for a wide range of clinical applications. Regular QC testing plays a vital role in maintaining system accuracy and reliability.

IMPLICATIONS FOR PRACTICE

This study underscores the importance of routine quality control procedures in ensuring the long-term stability and reliability of PET-CT systems. The robust performance of the uMI 550 supports its use in oncology and other diagnostic fields, providing clinicians with confidence in treatment decisions.

The role of medical physics experts in clinical trials: A guideline from the European Federation of Organisations for Medical Physics

The EFOMP working group on the Role of Medical Physics Experts (MPEs) in Clinical Trials was established in 2010, with experts from across Europe and different areas of medical physics. Their main aims were: (1) To develop a consensus guidance document for the work MPEs do in clinical trials across Europe. (2) Complement the work by American colleagues in AAPM TG 113 and guidance from National Member Organisations. (3) To cover external beam radiotherapy, brachytherapy, nuclear medicine, molecular radiotherapy, and imaging. This document outlines the main output from this working group. Giving guidance to MPEs, and indeed all Medical Physicists (MP) and MP trainees wishing to work in clinical trials. It also gives guidance to the wider multidisciplinary team, advising where MPEs must legally be involved, as well as highlighting areas where MPEs skills and expertise can really add value to clinical trials.

Lymphoma: The Added Value of Radiomics, Volumes and Global Disease Assessment

Lymphoma represents a condition that holds promise for cure with existing treatment modalities; nonetheless, the primary clinical obstacle lies in advancing therapeutic outcomes by pinpointing high-risk individuals who are unlikely to respond favorably to standard therapy. In this article, the authors will delineate the significant strides achieved in the lymphoma field, with a particular emphasis on the 3 prevalent subtypes: Hodgkin lymphoma, diffuse large B-cell lymphomas, and follicular lymphoma.

A Review on the Use of Imaging Biomarkers in Oncology Clinical Trials: Quality Assurance Strategies for Technical Validation

Imaging biomarkers (IBs) have been proposed in medical literature that exploit images in a quantitative way, going beyond the visual assessment by an imaging physician. These IBs can be used in the diagnosis, prognosis, and response assessment of several pathologies and are very often used for patient management pathways. In this respect, IBs to be used in clinical practice and clinical trials have a requirement to be precise, accurate, and reproducible. Due to limitations in imaging technology, an error can be associated with their value when considering the entire imaging chain, from data acquisition to data reconstruction and subsequent analysis. From this point of view, the use of IBs in clinical trials requires a broadening of the concept of quality assurance and this can be a challenge for the responsible medical physics experts (MPEs). Within this manuscript, we describe the concept of an IB, examine some examples of IBs currently employed in clinical practice/clinical trials and analyze the procedure that should be carried out to achieve better accuracy and reproducibility in their use. We anticipate that this narrative review, written by the components of the EFOMP working group on "the role of the MPEs in clinical trials"-imaging sub-group, can represent a valid reference material for MPEs approaching the subject.

Predictive value on advance hodgkin lymphoma treatment outcome of end-of treatment FDG PET/CT in the HD0607 clinical trial

The Lugano classification for response assessment in lymphoma recommends the use of the 5-point-scale Deauville Score (DS) to assess response evaluation of end-of-treatment FDG-PET/CT (eotPET) in Hodgkin Lymphoma (HL); nevertheless, there is a paucity of data on its accuracy and reproducibility. We focus here on the cohort of advanced stage IIb-IV HL patients enrolled in the HD0607 clinical trial (NCT identifier 00795613) that having had a negative interim PET performed 6 cycles of ABVD (Doxorubicin, Vinblastine, Vincristine and Dacarbazine) and then performed an eotPET. Negative patients were randomized to radiotherapy and no further treatment while positive patients were treated based on local policies. eotPET was re-evaluated independently by two readers evaluated and progression free survival was analysed (PFS). eotPET of 254 patients were analysed. The median follow-up was 43 months. The best receiver operator characteristics cut-off values to distinguish positive and negative patients was 4. The area-under-the-curve was 0.81 (95%CI, 0.70-0.91). Three-years PFS was 0.95 (95% CI 0.90-0.97) in eotPET negative and 0.22 (95% CI 0.11-0.43) in eotPET positive. DS demonstrated a good reproducibility of positivity/negativity between the readers consensus and local site evaluation where the agreement occurred on 95.0% of patients. The present study demonstrates that eotPET is an accurate tool to predict treatment outcome in HL and confirms the appropriateness of the Lugano classification for eotPET evaluation.

Variability in PET image quality and quantification measured with a permanently filled 68Ge-phantom: a multi-center study

BACKGROUND

This study evaluated, as a snapshot, the variability in quantification and image quality (IQ) of the clinically utilized PET [¹⁸F]FDG whole-body protocols in Finland using a NEMA/IEC IQ phantom permanently filled with ⁶⁸Ge.

METHODS

The phantom was imaged on 14 PET-CT scanners, including a variety of models from two major vendors. The variability of the recovery coefficients (RC_max, RC_mean and RC_peak) of the hot spheres as well as percent background variability (PBV), coefficient of variation of the background (COV_BG) and accuracy of corrections (AOC) were studied using images from clinical and standardized protocols with 20 repeated measurements. The ranges of the RCs were also compared to the limits of the EARL ¹⁸F standards 2 accreditation (EARL2). The impact of image noise on these parameters was studied using averaged images (AVIs).

RESULTS

The largest variability in RC values of the routine protocols was found for the RC_max with a range of 68% and with 10% intra-scanner variability, decreasing to 36% when excluding protocols with suspected cross-calibration failure or without point-spread-function (PSF) correction. The RC ranges of individual hot spheres in routine or standardized protocols or AVIs fulfilled the EARL2 ranges with two minor exceptions, but fulfilling the exact EARL2 limits for all hot spheres was variable. RC_peak was less dependent on averaging and reconstruction parameters than RC_max and RC_mean. The PBV, COV_BG and AOC varied between 2.3-11.8%, 9.6-17.8% and 4.8-32.0%, respectively, for the routine protocols. The RC ranges, PBV and COV_BG were decreased when using AVIs. With AOC, when excluding routine protocols without PSF correction, the maximum value dropped to 15.5%.

CONCLUSION

The maximum variability of the RC values for the [¹⁸F]FDG whole-body protocols was about 60%. The RC ranges of properly cross-calibrated scanners with PSF correction fitted to the EARL2 RC ranges for individual sphere sizes, but fulfilling the exact RC limits would have needed further optimization. RC_peak was the most robust RC measure. Besides COV_BG, also RCs and PVB were sensitive to image noise.

A tri-modal tissue-equivalent anthropomorphic phantom for PET, CT and multi-parametric MRI radiomics

PURPOSE

Radiomics has emerged as an advanced image processing methodology to define quantitative imaging biomarkers for prognosis and prediction of treatment response and outcome. The development of quantitative imaging biomarkers requires careful analysis to define their accuracy, stability and reproducibility through phantom measurements. Few efforts were devoted to develop realistic anthropomorphic phantoms. In this work, we developed a multimodality image phantom suitable for PET, CT and multiparametric MRI imaging.

METHODS

A tissue-equivalent gel-based mixture was designed and tested for compatibility with different imaging modalities. Calibration measurements allowed to assess gel composition to simulate PET, CT and MRI contrasts of oncological lesions. The characterized gel mixture was used to create realistic synthetic lesions (e.g. lesions with irregular shape and non-uniform image contrast), to be inserted in a standard anthropomorphic phantom. In order to show phantom usefulness, issues related to accuracy, stability and reproducibility of radiomic biomarkers were addressed as proofs-of-concept.

RESULTS

The procedure for gel preparation was straightforward and the characterized gel mixture allowed to mime simultaneously oncological lesion contrast in CT, PET and MRI imaging. Proofs-of-concept studies suggested that phantom measurements can be customized for specific clinical situations and radiomic protocols.

CONCLUSIONS

We developed a strategy to manufacture an anthropomorphic, tissue-equivalent, multimodal phantom to be customized on specific radiomics protocols, for addressing specific methodological issues both in mono and multicentric studies.

The 18F phantom clinical trials qualification for 18F-FDG-PET scanning adopted by GELTAMO (Grupo Español de Linfomas/Trasplante Autólogo de Médula Ósea)

INTRODUCTION AND OBJECTIVES

Since different PET/CT (Positron Emission Tomography/Computed Tomography) scanners give different qualitative readings, a program for clinical trial qualification (CTQ) is mandatory to guarantee a reliable and reproducible use of PET/CT in prospective multi-centre clinical trials. Within this work we will show the results carried out in performing CTQ in Spain.

MATERIALS AND METHODS

We set up, under the auspices of Grupo Español de Linfomas/Trasplante Autólogo de Médula Osea (GELTAMO), a CTQ program consisting of the acquisition and analysis of 18F uniformity and image quality phantoms for the reduction of inter-scanner variability (ISV). The ISV was estimated on background activity concentration (BAC) and sphere to background ratio (SBR) and defined as their 95% confidence level.

RESULTS

Twenty-six out of 27 (96%) scanners fulfilled the CTQ requirements. The CTQ was fulfilled at the first round in 27% of the cases, while in 38%, 15% and 20%, two, three or more than three iterations, were required, respectively. The mean CTQ time was (1.8 ± 1.4) months (range: 0.3-4.6). The ISV in BAC and SBR were 20.3% and 67.7%.

CONCLUSIONS

The CTQ proven to be a reliable tool to reduce ISV. This enabled to set-up clinical trials in which PET/CT was used to evaluate different clinical endpoints.

The impact of time-of-flight, resolution recovery, and noise modelling in reconstruction algorithms in non-solid-state detectors PET/CT scanners: - multi-centric comparison of activity recovery in a 68Ge phantom

The reconstruction algorithms implemented on PET/CT scanners offer gain in activity recovery of small lesions at an extent that is not full known yet. METHODS: A cylindrical phantom with warm background and hot spheres filled with a ⁶⁸Ge epoxy was acquired with four non-state-solid-detectors PET/CT scanners: mCT, Ingenuity TF, Discovery 710, and IQ. Images were reconstructed switching on and off time-of-flight (TOF), point spread function (PSF) modelling, and Bayesian penalised likelihood (BPL). Images were reconstructed with the default parameters recommended by the manufacturers. The recovery coefficient (RC_max), defined as the ratio of the measured maximum activity concentration in each sphere and the actual one, and the coefficient of variation (CoV_BAC) defined as the ratio of the standard deviation and the average of background activity concentration were measured. RESULTS: While with IR alone, complete recovery of the activity concentration is achieved down to the 22 mm diameter's sphere, with TOF, TOF + PSF and BPL it is achieved down to the 17 mm diameter one. At smaller dimensions, the difference among the various studied reconstruction algorithms is substantial for the 13- and 17-mm diameters' spheres for all scanners and for all reconstructions with a considerable gain in RCmax when PSF and BPL are used. At 10 mm diameter's sphere the difference among the algorithms is significantly reduced, except for BPL which still guarantees a gain in RCmax.

Does a 6-point scale approach to post-treatment 18F-FDG PET-CT allow to improve response assessment in head and neck squamous cell carcinoma? A multicenter study

PURPOSE

Response assessment to definitive non-surgical treatment for head and neck squamous cell carcinoma (HNSCC) is centered on the role of 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET-CT) 12 weeks after treatment. The 5-point Hopkins score is the only qualitative system available for standardized reporting, albeit limited by suboptimal positive predictive value (PPV). The aim of our study was to explore the feasibility and assess the diagnostic accuracy of an experimental 6-point scale ("Cuneo score").

METHODS

We performed a retrospective, multicenter study on HNSCC patients who received a curatively-intended, radiation-based treatment. A centralized, independent qualitative evaluation of post-treatment FDG-PET/CT scans was undertaken by 3 experienced nuclear medicine physicians who were blinded to patients' information, clinical data, and all other imaging examinations. Response to treatment was evaluated according to Hopkins, Cuneo, and Deauville criteria. The primary endpoint of the study was to evaluate the PPV of Cuneo score in assessing locoregional control (LRC). We also correlated semi-quantitative metabolic factors as included in PERCIST and EORTC criteria with disease outcome.

RESULTS

Out of a total sample of 350 patients from 11 centers, 119 subjects (oropharynx, 57.1%; HPV negative, 73.1%) had baseline and post-treatment FDG-PET/CT scans fully compliant with EANM 1.0 guidelines and were therefore included in our analysis. At a median follow-up of 42 months (range 5-98), the median locoregional control was 35 months (95% CI, 32-43), with a 74.5% 3-year rate. Cuneo score had the highest diagnostic accuracy (76.5%), with a positive predictive value for primary tumor (Tref), nodal disease (Nref), and composite TNref of 42.9%, 100%, and 50%, respectively. A Cuneo score of 5-6 (indicative of residual disease) was associated with poor overall survival at multivariate analysis (HR 6.0; 95% CI, 1.88-19.18; p = 0.002). In addition, nodal progressive disease according to PERCIST criteria was associated with worse LRC (OR for LR failure, 5.65; 95% CI, 1.26-25.46; p = 0.024) and overall survival (OR for death, 4.81; 1.07-21.53; p = 0.04).

CONCLUSIONS

In the frame of a strictly blinded methodology for response assessment, the feasibility of Cuneo score was preliminarily validated. Prospective investigations are warranted to further evaluate its reproducibility and diagnostic accuracy.

Evaluation of PET quantitation accuracy among multiple discovery IQ PET/CT systems via NEMA image quality test

Introduction

Quantitative imaging biomarkers are becoming usual in oncology for assessing therapy response. The harmonization of image quantitation reporting has become of utmost importance due to the multi-center trials increase. The NEMA image quality test is often considered for the evaluation of quantitation and is more accurate with a radioactive solid phantom that reduces variability. The goal of this project is to determine the level of variability among imaging centers if acquisition and imaging protocol parameters are left to the center’s preference while all other parameters are fixed including the scanner type.

Methods

A NEMA-IQ phantom filled with radioactive ⁶⁸Ge solid resin was imaged in five clinical sites throughout Europe. Sites reconstructed data with OSEM and BSREM algorithms applying the sites’ clinical parameters. Images were analyzed according with the NEMA-NU2-2012 standard using the manufacturer-provided NEMA tools to calculate contrast recovery (CR) and background variability (BV) for each sphere and the lung error (LE) estimation. In addition, a ¹⁸F-filled NEMA-IQ phantom was also evaluated to obtain a gauge for variability among centers when the sites were provided with identical specific instructions for acquisition and reconstruction protocol (the aggregate of data from 12 additional sites is presented).

Results

The data using the ⁶⁸Ge solid phantom showed no statistical differences among different sites, proving a very good reproducibility among the PET center models even if dispersion of data is higher with OSEM compared to BSREM. Furthermore, BSREM shows better CR and comparable BV, while LE is slightly reduced. Two centers exhibit significant differences in CR and BV values for the ¹⁸F NEMA NU2-2012 experiments; these outlier results are explained.

Conclusion

The same PET system type from the various sites produced similar quantitative results, despite allowing each site to choose their clinical protocols with no restriction on data acquisition and reconstruction parameters. BSREM leads to lower dispersion of quantitative data among different sites. A solid radioactive phantom may be recommended to qualify the sites to perform quantitative imaging.

Treatment response assessment in [18F]FDG-PET/CT oncology scans: Impact of count statistics variation and reconstruction protocol

PURPOSE

To investigate influences of reconstruction algorithms and count statistics variation on quantification and treatment response assessment in cancer patients, by using a large field of view-FOV scanner.

METHODS

54 cancer patients underwent PET/CT scan: 1) at baseline: 1.5 min/FOV, reconstructed by ordered-subset expectation maximization + point-spread-function-OSEM-PSF and bayesian penalised-likelihood-BPL algorithm 2) at restaging: 2 min/FOV, reconstructed also at 1.5 and 1 min/FOV, using OSEM-PSF and BPL. SUL (lean-body mass SUV) peak and max were measured for each target-lesion (n = 59). Differences in quantification obtained from datasets with different reconstruction algorithms and different time/FOV were evaluated. For any pair of PET datasets, metabolic response was assessed by using SULpeak, with a threshold of 30% in variation considered as significant.

RESULTS

Both at baseline and restaging, SULpeak and max values were higher in BPL reconstructions than in OSEM-PSF (p < 0.0001). SULpeak at different time/FOV reconstructions showed no statistically significant differences both with OSEM-PSF and BPL; SULmax depended on acquisition time (p < 0.05). In 56/59 lesions (95%) therapy response was concordant regardless count statistics variation and reconstruction algorithm; 2/59 (3%) showed different responses according to count statistics, both for OSEM-PSF and BPL; in 1/59 lesion (2%) response was different depending on reconstruction algorithm used.

CONCLUSIONS

BPL provided higher SULpeak and max than OSEM-PSF. With a large FOV/high sensitivity scanner, variation of time/FOV in restaging PET scans gave stable and reproducible results in terms of SULpeak, both for OSEM-PSF and BPL. Thus, metabolic response defined by SULpeak variation proved to be quite independent from count statistics.

Multicenter study of quantitative PET system harmonization using NIST-traceable 68Ge/68Ga cross-calibration kit

PURPOSE

The present study aimed to define the errors in SUV and demonstrate the feasibility of SUV harmonization among contemporary PET/CT scanners using a novel National Institute of Standards and Technology (NIST)-traceable ⁶⁸Ge/⁶⁸Ga source as the reference standard.

METHODS

We used ⁶⁸Ge/⁶⁸Ga dose calibrator and PET sources made with same batch of ⁶⁸Ge/⁶⁸Ga embedded in epoxy that is traceable to the NIST standard. Bias in the amount of radioactivity and the radioactive concentrations measured by the dose calibrators and PET/CT scanners, respectively, was determined at five Japanese sites. We adjusted optimal dial setting of the dose calibrators and PET reconstruction parameters to close the actual amount of radioactivity and the radioactive concentration, respectively, of the NIST-traceable ⁶⁸Ge/⁶⁸Ga sources to harmonize SUV. Errors in SUV before and after harmonization were then calculated at each site.

RESULTS

The average bias in the amount of radioactivity and the radioactive concentrations measured by dose calibrator and PET scanner was -4.94% and -12.22%, respectively, before, and -0.14% and -4.81%, respectively, after harmonization. Corresponding averaged errors in SUV measured under clinical conditions were underestimated by 7.66%, but improved by -4.70% under optimal conditions.

CONCLUSION

Our proposed method using an NIST-traceable ⁶⁸Ge/⁶⁸Ga source identified bias in values obtained using dose calibrators and PET scanners, and reduced SUV variability to within 5% across different models of PET scanners at five sites. Our protocol using a standard source has considerable potential for harmonizing the SUV when contemporary PET scanners are involved in multicenter studies.

Automatic liver detection and standardised uptake value evaluation in whole-body Positron Emission Tomography/Computed Tomography scans

BACKGROUND AND OBJECTIVE

Standardised Uptake Value (SUV), in clinical research and practice, is a marker of tumour avidity in Positron Emission Tomography/Computed Tomography (PET/CT). Since many technical, physical and physiological factors affect the SUV absolute measurement, the liver uptake is often used as reference value both in quantitative and semi-quantitative evaluation. The purpose of this investigation was to automatically detect the liver position in whole-body PET/CT scans and extract its average SUV value.

METHODS

We developed an algorithm, called LIver DEtection Algorithm (LIDEA), that analyses PET/CT scans, and under the assumption that the liver is a large homogeneous volume near the centre of mass of the patient, finds its position and automatically places a region of interest (ROI) in the liver, which is used to calculate the average SUV. The algorithm was validated on a population of 630 PET/CT scans coming from more than 60 different scanners. The SUV was also calculated by manually placing a large ROI in the liver.

RESULTS

LIDEA identified the liver with a 97.3% sensitivity with PET/CT images only and reached a 98.9% correct detection rate when using the co-registered CT scan to avoid liver misidentification in the right lung. The average liver SUV obtained with LIDEA was successfully validated against its manual assessment, with no systematic difference (0.11 ± 0.36 SUV units) and a R²=0.89 correlation coefficient.

CONCLUSIONS

LIDEA proved to be a reliable tool to automatically identify and extract the average SUV of the liver in oncological whole-body PET/CT scans.

Measuring temporal stability of positron emission tomography standardized uptake value bias using long-lived sources in a multicenter network

Positron emission tomography (PET) is a quantitative imaging modality, but the computation of standardized uptake values (SUVs) requires several instruments to be correctly calibrated. Variability in the calibration process may lead to unreliable quantitation. Sealed source kits containing traceable amounts of [Formula: see text] were used to measure signal stability for 19 PET scanners at nine hospitals in the National Cancer Institute's Quantitative Imaging Network. Repeated measurements of the sources were performed on PET scanners and in dose calibrators. The measured scanner and dose calibrator signal biases were used to compute the bias in SUVs at multiple time points for each site over a 14-month period. Estimation of absolute SUV accuracy was confounded by bias from the solid phantoms' physical properties. On average, the intrascanner coefficient of variation for SUV measurements was 3.5%. Over the entire length of the study, single-scanner SUV values varied over a range of 11%. Dose calibrator bias was not correlated with scanner bias. Calibration factors from the image metadata were nearly as variable as scanner signal, and were correlated with signal for many scanners. SUVs often showed low intrascanner variability between successive measurements but were also prone to shifts in apparent bias, possibly in part due to scanner recalibrations that are part of regular scanner quality control. Biases of key factors in the computation of SUVs were not correlated and their temporal variations did not cancel out of the computation. Long-lived sources and image metadata may provide a check on the recalibration process.

Evaluation of Cross-Calibrated 68Ge/68Ga Phantoms for Assessing PET/CT Measurement Bias in Oncology Imaging for Single- and Multicenter Trials

Quantitative PET imaging is an important tool for clinical trials evaluating the response of cancers to investigational therapies. The standardized uptake value, used as a quantitative imaging biomarker, is dependent on multiple parameters that may contribute bias and variability. The use of long-lived, sealed PET calibration phantoms offers the advantages of known radioactivity activity concentration and simpler use than aqueous phantoms. We evaluated scanner and dose calibrator sources from two batches of commercially available kits, together at a single site and distributed across a local multicenter PET imaging network. We found that radioactivity concentration was uniform within the phantoms. Within the regions of interest drawn in the phantom images, coefficients of variation of voxel values were less than 2%. Across phantoms, coefficients of variation for mean signal were close to 1%. Biases of the standardized uptake value estimated with the kits varied by site and were seen to change in time by approximately ±5%. We conclude that these biases cannot be assumed constant over time. The kits provide a robust method to monitor PET scanner and dose calibrator biases, and resulting biases in standardized uptake values.

The Strategies to Homogenize PET/CT Metrics: The Case of Onco-Haematological Clinical Trials

Positron emission tomography (PET) has been a widely used tool in oncology for staging lymphomas for a long time. Recently, several large clinical trials demonstrated its utility in therapy management during treatment, paving the way to personalized medicine. In doing so, the traditional way of reporting PET based on the extent of disease has been complemented by a discrete scale that takes in account tumour metabolism. However, due to several technical, physical and biological limitations in the use of PET uptake as a biomarker, stringent rules have been used in clinical trials to reduce the errors in its evaluation. Within this manuscript we will describe shortly the evolution in PET reporting, examine the main errors in uptake measurement, and analyse which strategy the clinical trials applied to reduce them.

Baseline Total Metabolic Tumor Volume Measured with Fixed or Different Adaptive Thresholding Methods Equally Predicts Outcome in Peripheral T Cell Lymphoma

The purpose of this study was to compare in a large series of peripheral T cell lymphoma, as a model of diffuse disease, the prognostic value of baseline total metabolic tumor volume (TMTV) measured on ¹⁸F-FDG PET/CT with adaptive thresholding methods with TMTV measured with a fixed 41% SUV_max threshold method.

METHODS

One hundred six patients with peripheral T cell lymphoma, staged with PET/CT, were enrolled from 5 Lymphoma Study Association centers. In this series, TMTV computed with the 41% SUV_max threshold is a strong predictor of outcome. On a dedicated workstation, we measured the TMTV with 4 adaptive thresholding methods based on characteristic image parameters: Daisne (Da) modified, based on signal-to-background ratio; Nestle (Ns), based on tumor and background intensities; Fit, including a 3-dimensional geometric model based on spatial resolution (Fit); and Black (Bl), based on mean SUV_max The TMTV values obtained with each adaptive method were compared with those obtained with the 41% SUV_max method. Their respective prognostic impacts on outcome prediction were compared using receiver-operating-characteristic (ROC) curve analysis and Kaplan-Meier survival curves.

RESULTS

The median value of TMTV_41%, TMTV_Da, TMTV_Ns, TMTV_Fit, and TMTV_Bl were, respectively, 231 cm³ (range, 5-3,824), 175 cm³ (range, 8-3,510), 198 cm³ (range, 3-3,934), 175 cm³ (range, 8-3,512), and 333 cm³ (range, 3-5,113). The intraclass correlation coefficients were excellent, from 0.972 to 0.988, for TMTV_Da, TMTV_Fit, and TMTV_Ns, and less good for TMTV_Bl (0.856). The mean differences obtained from the Bland-Altman plots were 48.5, 47.2, 19.5, and -253.3 cm³, respectively. Except for Black, there was no significant difference within the methods between the ROC curves (P > 0.4) for progression-free survival and overall survival. Survival curves with the ROC optimal cutoff for each method separated the same groups of low-risk (volume ≤ cutoff) from high-risk patients (volume > cutoff), with similar 2-y progression-free survival (range, 66%-72% vs. 26%-29%; hazard ratio, 3.7-4.1) and 2-y overall survival (79%-83% vs. 50%-53%; hazard ratio, 3.0-3.5).

CONCLUSION

The prognostic value of TMTV remained quite similar whatever the methods, adaptive or 41% SUV_max, supporting its use as a strong prognosticator in lymphoma. However, for implementation of TMTV in clinical trials 1 single method easily applicable in a multicentric PET review must be selected and kept all along the trial.