Randomized controlled trials on PET: a systematic review of topics, design, and quality

Use of 18F-NaF PET in the staging of skeletal metastases of newly diagnosed, high-risk prostate cancer patients: a nationwide cohort study

OBJECTIVE

To determine whether preoperative staging of high-risk prostate cancer with 18F-sodium-fluoride (18F-NaF) positron emission tomography (PET) reduces the risk of skeletal metastases.

DESIGN

Nationwide, population-based cohort study using real-world data.

SETTING

The study used national health registries, including all sites in Denmark from 2011 to 2018.

PARTICIPANTS

Newly diagnosed high-risk prostate cancer patients who underwent radical prostatectomy from 2011 to 2018. Patients were stratified into two groups according to the preoperative imaging modality of either 18F-NaF PET or bone scintigraphy.

MAIN OUTCOME MEASURES

The risk of skeletal-related events (SREs) as a proxy for skeletal metastases following radical prostatectomy. The secondary endpoint was overall survival.

RESULTS

Between 1 January 2011 and 31 December 2018, 4183 high-risk patients underwent radical prostatectomy. Of these patients, 807 (19.3%) underwent 18F-NaF PET and 2161 (51.7%) underwent bone scintigraphy. The remaining 30% were examined by a different imaging method or did not undergo imaging. Using the inverse probability of treatment weighting to control potential confounding, the HR of experiencing an SRE for patients in the 18F-NaF PET group versus the bone scintigraphy group was 1.15 (95% CI 0.86 to 1.54). The 3-year survival rates were 97.4% (95% CI 96.1 to 98.7) and 97.1% (95% CI 96.4 to 97.9) for patients receiving 18F-NaF PET and bone scintigraphy, respectively.

CONCLUSION

Patients with high-risk prostate cancer undergoing preoperative staging with 18F-NaF PET did not display a lower risk of developing SREs after prostatectomy compared with patients undergoing bone scintigraphy. The survival rates were similar between the two groups.

The Emerging Role of PET/MR Imaging in Gynecologic Cancers

This article summarizes recent advances in PET/MR imaging in gynecologic cancers and the emerging clinical value of PET/MR imaging in the management of the 3 most common gynecologic malignancies: cervical, endometrial, and ovarian cancers. PET/MR imaging offers superior soft tissue contrast, improved assessment of primary tumor involvement because of high-resolution multiplanar reformats, and functional MR techniques such as diffusion-weighted MR imaging and dynamic contrast-enhanced MR imaging. This article discusses the challenges, future directions, and technical advances of PET/MR imaging, and the emerging new multimodality, multiparametric imaging techniques for integrating morphologic, functional, and molecular imaging data.

Biomarker-Guided Non-Adaptive Trial Designs in Phase II and Phase III: A Methodological Review

Biomarker-guided treatment is a rapidly developing area of medicine, where treatment choice is personalised according to one or more of an individual’s biomarker measurements. A number of biomarker-guided trial designs have been proposed in the past decade, including both adaptive and non-adaptive trial designs which test the effectiveness of a biomarker-guided approach to treatment with the aim of improving patient health. A better understanding of them is needed as challenges occur both in terms of trial design and analysis. We have undertaken a comprehensive literature review based on an in-depth search strategy with a view to providing the research community with clarity in definition, methodology and terminology of the various biomarker-guided trial designs (both adaptive and non-adaptive designs) from a total of 211 included papers. In the present paper, we focus on non-adaptive biomarker-guided trial designs for which we have identified five distinct main types mentioned in 100 papers. We have graphically displayed each non-adaptive trial design and provided an in-depth overview of their key characteristics. Substantial variability has been observed in terms of how trial designs are described and particularly in the terminology used by different authors. Our comprehensive review provides guidance for those designing biomarker-guided trials.

PET-CT in the UK: current status and future directions

Combined positron-emission tomography and computed tomography (PET-CT) has taken the oncological world by storm since being introduced into the clinical domain in the early 21(st) century and is firmly established in the management pathway of many different tumour types. Non-oncological applications of PET-CT represent a smaller but steadily growing area of interest. PET-CT continues to be the focus of a large number of research studies and keeping up-to-date with the literature is important but represents a challenge. Consequently guidelines recommending PET-CT usage need to be revised regularly to encompass new developments. The purpose of this article is twofold: first, it provides a detailed review of the evidence-base underpinning the major uses of PET-CT in clinical practice, which may be of value to a wide-range of individuals, including those directly involved with PET-CT and to a much larger group with limited exposure, but for whom a précis of the current state-of-play may help inform other radiology and multidisciplinary team (MDT) work; the second purpose is as a companion to revised guidelines on evidence-based indications for PET-CT in the UK (being published concurrently) providing a detailed commentary on new indications with a summary of emerging data supporting these additional clinical uses of the technique.

Evaluation of the Efficacy of Targeted Imaging Agents

This paper presents our adaptation of Fryback and Thornbury's hierarchical scheme for modeling the efficacy of diagnostic imaging systems. The original scheme was designed to evaluate new medical imaging systems but is less successful when applied to evaluate new radiopharmaceuticals. The proposed adaptation, which is specifically directed toward evaluating targeted imaging agents, has 6 levels: in vitro characterization, in vivo animal studies, initial human studies, impact on clinical care (change in management), impact on patient outcome, and societal efficacy. These levels, particularly the first four, implicitly define the sequence of studies needed to move an agent from the radiochemistry synthesis laboratory to the clinic. Completion of level 4 (impact on clinical care) should be sufficient for initial approval and reimbursement. We hope that the adapted scheme will help streamline the process and assist in bringing new targeted radiopharmaceuticals to approval over the next few years.

FDG and Beyond

Although many PET tracers are in use, FDG still is the most widely used in clinical oncology practice. FDG therefore deserves an in-depth discussion, which is even more interesting because of the huge increase in the molecular biology of glucose metabolism. Obviously, other tracers are of increasing importance as well, and these will be discussed in short.

Diagnostic evaluation for interventional bronchoscopists and radiologists in lung cancer practice

The global epidemic of lung cancer shows no signs of abating. It is generally accepted that accurate and cost-efficient diagnostic evaluation is the first important step to achieve the best outcomes of treatment. This is true in the context of disease confirmation, treatment planning, treatment monitoring, detection of and management of treatment failure or prognostication. Fortunately, major advances in the diagnostic evaluation of lung cancer have been made in the past three decades allowing more patients to get the appropriate treatment at the right time. This paper outlines how computed tomography, positron emission tomography/computed tomography and endobronchial ultrasound contribute to lung cancer management and discuss their strengths and weaknesses and their complimentary roles at different stages of lung cancer management. Due to financial constraint and reimbursement restrictions, not all clinically important advances in the diagnostic evaluation of lung cancer have been readily accepted into routine clinical care. This enforces the need to maintain ongoing dialogue between cancer clinicians, imaging specialists and health-care economists.

Cost-effectiveness of PET and PET/computed tomography: a systematic review

The development of clinical diagnostic procedures comprises early-phase and late-phase studies to elucidate diagnostic accuracy and patient outcome. Economic assessments of new diagnostic procedures compared with established work-ups indicate additional cost for 1 additional unit of effectiveness measure by means of incremental cost-effectiveness ratios when considering the replacement of the standard regimen by a new diagnostic procedure. This article discusses economic assessments of PET and PET/computed tomography reported until mid-July 2014. Forty-seven studies on cancer and noncancer indications were identified but, because of the widely varying scope of the analyses, a substantial amount of work remains to be done.

Incidental colonic focal FDG uptake on PET/CT: can the maximum standardized uptake value (SUVmax) guide us in the timing of colonoscopy?

PURPOSE

In patients undergoing (18)F-FDG PET/CT, incidental colonic focal lesions can be indicative of inflammatory, premalignant or malignant lesions. The maximum standardized uptake value (SUVmax) of these lesions, representing the FDG uptake intensity, might be helpful in differentiating malignant from benign lesions, and thereby be helpful in determining the urgency of colonoscopy. The aim of our study was to assess the incidence and underlying pathology of incidental PET-positive colonic lesions in a large cohort of patients, and to determine the usefulness of the SUVmax in differentiating benign from malignant pathology.

METHODS

The electronic records of all patients who underwent FDG PET/CT from January 2010 to March 2013 in our hospital were retrospectively reviewed. The main indications for PET/CT were: characterization of an indeterminate mass on radiological imaging, suspicion or staging of malignancy, and suspicion of inflammation. In patients with incidental focal FDG uptake in the large bowel, data regarding subsequent colonoscopy were retrieved, if performed within 120 days. The final diagnosis was defined using colonoscopy findings, combined with additional histopathological assessment of the lesion, if applicable.

RESULTS

Of 7,318 patients analysed, 359 (5 %) had 404 foci of unexpected colonic FDG uptake. In 242 of these 404 lesions (60 %), colonoscopy follow-up data were available. Final diagnoses were: adenocarcinoma in 25 (10 %), adenoma in 90 (37 %), and benign in 127 (53 %). The median [IQR] SUVmax was significantly higher in adenocarcinoma (16.6 [12 - 20.8]) than in benign lesions (8.2 [5.9 - 10.1]; p < 0.0001), non-advanced adenoma (8.3 [6.1 - 10.5]; p < 0.0001) and advanced adenoma (9.7 [7.2 - 12.6]; p < 0.001). The receiver operating characteristic curve of SUVmax for malignant versus nonmalignant lesions had an area under the curve of 0.868 (SD ± 0.038), the optimal cut-off value being 11.4 (sensitivity 80 %, specificity 82 %, positive predictive value 34 %, negative predictive value 98 %).

CONCLUSION

In these patients with incidental colonic focal activity undergoing PET/CT (the largest series published to date), malignancies had significantly higher SUVmax values than all other types of lesions. However, SUVmax could not distinguish between benign lesions and adenomas. In conclusion, all incidental findings in the colon should be further evaluated and lesions with SUVmax ≥11.4 should be evaluated without delay.

The move from accuracy studies to randomized trials in PET: current status and future directions

Since the influential study by van Tinteren et al. published in The Lancet in 2002, there have been an increasing number of diagnostic randomized controlled trials (RCTs) investigating the benefit of PET. If they provide valid and useful information on the benefit, these studies can play an important role in informing guideline developers and policy makers. Our aim was to investigate how far the nuclear medicine community has come on its way from accuracy studies to RCTs and which issues we have to take into account in planning future studies.

METHODS

We conducted a systematic review of diagnostic randomized trials, in which PET was applied in only one arm. We covered published studies as well as registered unpublished and planned studies. We considered 3 quality indicators related to the usefulness of a trial to generate evidence for a clinical benefit: use of patient-important outcome, sufficient sample size, and current standard as comparator.

RESULTS

Fourteen published and 15 planned studies were identified. Five of the published studies and 12 of the planned studies did not use a patient-important outcome. Sample sizes were often so small that a significant result could be expected only under the assumption of a substantial reduction in the event rate. Comparators typically reflected the current standard.

CONCLUSION

If we consider the traditional areas of primary diagnosis, staging, and follow-up, then the number and quality of RCTs on PET is currently not sufficient to provide a major source for evidence-based decisions on the clinical benefit of PET. There will also be a future need in these traditional areas to deduce the clinical benefit of PET from the results of accuracy studies. The situation may be more favorable for the areas of treatment planning and response evaluation. Choice of patient-important outcomes and sufficient sample sizes are crucial issues in planning RCTs to demonstrate the clinical benefit of using PET.

Transconvolution and the virtual positron emission tomograph--a new method for cross calibration in quantitative PET∕CT imaging

PURPOSE

Positron emission tomography (PET)∕computed tomography (CT) measurements on small lesions are impaired by the partial volume effect, which is intrinsically tied to the point spread function of the actual imaging system, including the reconstruction algorithms. The variability resulting from different point spread functions hinders the assessment of quantitative measurements in clinical routine and especially degrades comparability within multicenter trials. To improve quantitative comparability there is a need for methods to match different PET∕CT systems through elimination of this systemic variability. Consequently, a new method was developed and tested that transforms the image of an object as produced by one tomograph to another image of the same object as it would have been seen by a different tomograph. The proposed new method, termed Transconvolution, compensates for differing imaging properties of different tomographs and particularly aims at quantitative comparability of PET∕CT in the context of multicenter trials.

METHODS

To solve the problem of image normalization, the theory of Transconvolution was mathematically established together with new methods to handle point spread functions of different PET∕CT systems. Knowing the point spread functions of two different imaging systems allows determining a Transconvolution function to convert one image into the other. This function is calculated by convolving one point spread function with the inverse of the other point spread function which, when adhering to certain boundary conditions such as the use of linear acquisition and image reconstruction methods, is a numerically accessible operation. For reliable measurement of such point spread functions characterizing different PET∕CT systems, a dedicated solid-state phantom incorporating (68)Ge∕(68)Ga filled spheres was developed. To iteratively determine and represent such point spread functions, exponential density functions in combination with a Gaussian distribution were introduced. Furthermore, simulation of a virtual PET system provided a standard imaging system with clearly defined properties to which the real PET systems were to be matched. A Hann window served as the modulation transfer function for the virtual PET. The Hann's apodization properties suppressed high spatial frequencies above a certain critical frequency, thereby fulfilling the above-mentioned boundary conditions. The determined point spread functions were subsequently used by the novel Transconvolution algorithm to match different PET∕CT systems onto the virtual PET system. Finally, the theoretically elaborated Transconvolution method was validated transforming phantom images acquired on two different PET systems to nearly identical data sets, as they would be imaged by the virtual PET system.

RESULTS

The proposed Transconvolution method matched different PET∕CT-systems for an improved and reproducible determination of a normalized activity concentration. The highest difference in measured activity concentration between the two different PET systems of 18.2% was found in spheres of 2 ml volume. Transconvolution reduced this difference down to 1.6%. In addition to reestablishing comparability the new method with its parameterization of point spread functions allowed a full characterization of imaging properties of the examined tomographs.

CONCLUSIONS

By matching different tomographs to a virtual standardized imaging system, Transconvolution opens a new comprehensive method for cross calibration in quantitative PET imaging. The use of a virtual PET system restores comparability between data sets from different PET systems by exerting a common, reproducible, and defined partial volume effect.

Die Notwendigkeit unabhängiger klinischer Studien aus der Sicht des Instituts für Qualität und Wirtschaftlichkeit im Gesundheitswesen

Die Ergebnisse klinischer, möglichst randomisierter kontrollierter Studien (RCT) bilden das Rückgrat von Entscheidungen zur Zulassung von Arzneimitteln und von Nutzenbewertungen medizinischer Methoden. Während Zulassungsstudien von Arzneimitteln häufig zumindest einige der für eine Nutzenbewertung relevanten Fragen beantworten, ist die Situation bei nichtmedikamentösen therapeutischen Methoden und diagnostischen Verfahren eine gänzlich andere, weil es hier keine vergleichbar hohen Anforderungen an eine Markteinführung gibt. Insgesamt muss festgestellt werden, dass es in der Vergangenheit für Hersteller oder Anbieter von medizinischen Methoden keine ausreichenden (finanziellen) Anreize gab und auch weiterhin nicht gibt, klinische Studien zum patientenrelevanten Nutzen durchzuführen, sowohl bei Arzneimitteln als auch insbesondere im nichtmedikamentösen Bereich. Daraus resultiert eine Lücke von Studien, die mit ausreichender Ergebnissicherheit in einem angemessenen Vergleich Daten zum patientenrelevanten Nutzen bzw. Zusatznutzen einer medizinischen Methode liefern. In diesem Zusammenhang ist es zweitrangig, ob es sich dabei um «unabhängige» Studien handelt, zumal «Abhängigkeiten» nie ausgeschlossen werden können und dort, wo sie nicht durch die Deklaration eines Sponsorings leicht erkennbar sind, besonders problematisch werden können. Das Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen (IQWiG) ist gerne bereit und dabei, zusammen mit Interessierten dafür zu werben, dass für wichtige Studienprojekte von klinischen Forschergruppen, die die Kriterien einer qualitativ hochwertigen patientenorientierten klinischen Studie zu einer relevanten Fragestellung erfüllen, angemessene Fördermöglichkeiten geschaffen werden.