Évaluation des thérapeutiques ciblées en tomographie par émission de positons

Thanks to breakthroughs in drug design, new kinds of treatment in oncology have been developed. These new molecules target usually a precise molecular pathway proved to be involved in the development of a malignant disease. This led to the concept of targeted therapy. Therefore, the accurate selection of patients who may experience a clinical benefit of such treatments and the way to assess the response are still challenging issues. Molecular imaging with radiolabeled compounds seemed to be a very promising tool, as for example PET with ¹⁸F FluoroDeoxyGlucose (FDG), which allows to assess and to predict the response to a tyrosine kinase inhibitors more efficiently than conventional imaging tools. FDG is only a surrogate marker of cell proliferation. The common tools (clinical and radiological assessment) are no longer sufficient to predict the clinical efficacy of these new drugs. Molecular imaging should be added in the design of clinical trials in order to detect earlier pharmacodynamic effects, to select responding patients and to provide proofs of efficacy of these non-cytotoxic compounds. Molecular imaging databases have to be created and cross-matched to tumor sample collections, providing consequently new “dynamic” pathological resources.     

Détection fortuite d’une synovite villonodulaire extra-articulaire du muscle psoas en tomographie par émission de positons au 18F-fluorodésoxyglucose

Pigmented villonodular synovitis (PVNS) is a benign but locally aggressive disorder, which commonly involves large joints. This article reports a rare case of an extra-articular PVNS located within the left psoas muscle. This lesion has been accidentally discovered during a follow-up FDG PET/CT. The patient was asymptomatic and did not undergo any surgery. This article reports that FDG PET/CT could be helpful for monitoring PVNS.     

Place de la tomographie par émission de positons (TEP) au [18F]FDG dans l’exploration des vascularites

[¹⁸F]fluorodeoxyglucose (¹⁸FDG) positron emission tomography (PET) is a noninvasive metabolic imaging modality that is well suited to the assessment of activity and extent of large vessel vasculitis, such as giant cell arteritis and Takayasu arteritis. PET could be more effective than magnetic resonance imaging in detecting the earliest stages of vascular wall inflammation. The visual grading of vascular [¹⁸F]FDG uptake makes it possible to discriminate arteritis from atherosclerosis, providing therefore high specificity. High sensitivity can be achieved provided scanning is performed during active inflammatory phase, preferably before starting corticosteroid treatment. Large scale prospective studies are needed to determine the exact value of PET imaging in assessing the large vessel vasculitis outcome and response to immunosuppressive treatment.     

Impact de la tomographie par émission de positons au 18fluorodésoxyglucose dans la prise en charge des cancers de primitif inconnu

Aim and methodThis retrospective study, performed on 37 patients, gave us the opportunity to evaluate the impact of ¹⁸F-FDG PET/CT for cancer of unknown primary (CUP). We first wanted to study the precision of the exam to detect the primary, after a negative check-up, for the extension of the disease, and to judge the impact of the results on management and survival of those patients.ResultThe PET/CT led to the detection of the primary for 14 patients out of 37, after a negative check-up composed of five exams on average. For 10 patients, the exam allows the detection of supplementary metastases. The management was changed after the exam in more than one third of the patients, but without any significant impact on the time of survival of these patients, for whom the prognostic is usually dismal.ConclusionThe ¹⁸F-FDG PET/CT appears a valuable tool for detection of primary, changing the management of many of the patients. These results must be completed by a prospective study, in particular to judge the impact of exam's results on the survival.     

Place de la tomographie d’émission de positons (TEP) pour l’évaluation thérapeutique et le suivi du cancer du sein

Positron emission tomography (PET) with fluorodeoxyglucose (FDG) is a nuclear imaging method whose interest in oncology has only grown over the past fifteen years. This article summarizes the results in monitoring and therapeutic evaluation of breast cancer. For the search of locoregional or distant recurrence, the performance of FDG-PET are very interesting. The impact of FDG-PET on the therapeutic management is undeniable. For therapeutic evaluation, this imaging is useful to evaluate the neoadjuvant chemotherapy and hormonotherapy efficacy. FDG-PET is indicated in cases of suspected recurrence (clinical, biological or imaging suspicious). It is the most sensitive exam for the detection of bone or visceral metastases. It allows the re-staging during a relapse proved whether local or remote, and can change the therapeutic management.     

La géométrie fractale pour l’analyse de signaux médicaux : état de l’art

The diagnostic interpretation of medical images is a complex task aiming to detect potential abnormalities. One of the most used features in this process is texture which is a key component in the human understanding of images. Many studies were conducted to develop algorithms for texture quantification. The relevance of fractal geometry in medical image analysis is justified by the proven self-similarity of anatomical objects when imaged with a finite resolution. Over the last years, fractal geometry was applied extensively in many medical signal analysis applications. The use of these geometries relies heavily on estimation of the fractal features. Various methods were proposed to estimate the fractal dimension or multifractal spectrum of a signal. This article presents an overview of these algorithms, the way they work, their benefits and limits, and their application in the field of medical signal analysis.     

La tomographie par émission de positons (TEP) hors oncologie : l’exploration du cerveau

Positron emission tomography (PET) allows evaluation of the central nervous system function. Imaging of regional cerebral blood flow and metabolism, and of several neurotransmission systems may be obtained using PET. PET quantification is accurate and has good test–retest reliability. For research purposes, PET has been used to study brain physiology, to explore neurological and psychiatric diseases patophysiology and for the new drugs research and development. FDG is the only PET radioligand with clinical application. Following criteria of evidence-based medicine, the clinical indications of FDG-PET are: evaluation of treated gliomas, presurgical study of partial refractory epilepsy and diagnosis of Alzheimer's disease when it is impossible to differentiate clinically from frontotemporal dementia.     

Évaluation de la perfusion et de la fonction contractile du myocarde à l’aide de l’analyse de Karhunen-Loeve en tomographie d’émission monophotonique myocardique synchronisée à l’ECG

GoalWe evaluated the diagnostic performance of the Karhunen–Loeve transform applied to myocardial gated SPECT. The previous studies showed that KLT images characterize myocardial perfusion (KL0) and contractile function (KL1).Method and material99mTc-gSPECT studies were performed in 101 patients (121 acquisitions) with suspected or known coronary artery disease. The images were evaluated using a five-point scoring system dividing the left ventricle into 11 segments. We compared the scores obtained by this semi-quantitative visual analysis of gSPECT and KLT images.Results and discussionThe agreement for perfusion and thickening scores was 94 and 95% respectively. Quantitative evaluation of KL0 and KL1 images by univariate and multivariate analysis was performed in the left ventricular ROI. Discriminant analysis characterized the acquisitions as normal or pathologic with a sensitivity of 95% and a specificity of 96% and positive and negative predictive values of 96 and 95%. These selection criteria were tested prospectively in 52 patients with similar results. KLT generates a synthesis of left ventricular perfusion and kinetics. It facilitates discrimination between normal and pathological acquisitions with high predictive values.     

Place de la tomographie par émission de positons dans la prise en charge des fièvres d’origine inconnue

FDG-PET has become an established diagnostic tool in oncology. Fluorodeoxyglucose is not a specific tracer for malignant lesions, as uptake depends on accumulation of FDG in cells with an increased glucose metabolism as it is also the case in inflammatory and infectious lesions. Thus, FDG-PET could be valuable in diagnosing patients with fever of unknown origin (FUO). The percentage of FDG-PET scans helpful in the diagnostic process in patients with FUO is estimated in average around 30%. However, more evaluating prospective studies should be awaited before integrating FDG-PET in clinical routine use in order to compare different techniques already validated (biology, radiology, conventional scintigraphic imaging), to evaluate its cost-effectiveness and to determine its place for the managment of FUO.     

Évaluation des paramètres et méthode de contrôle de qualité de la correction d’atténuation en tomographie par émission de positons

ObjectiveThe aim of this study is to evaluate the performance of the Computed Tomography based Attenuation Correction (CTAC) for Positron Emission Tomography (PET) data. Attenuation maps containing linear attenuation coefficients at 511 keV (LAC_511 keV) are calculated by trilinear conversion of Hounsfield Units (HU) obtained from CT slices after matrix size-reduction and gaussian filtering. Our work focusses on this trilinear conversion.Materials and methodsCT slices of an electron density phantom, composed of 17 cylindrical inserts made of different tissue-equivalent materials, were acquired using a Discovery ST4^® PET-CT. Data were processed with a customized version of CT quality control software, giving automatically the experimental conversion function: LAC_511 keV = f(HU). Furthermore, data from patient datasets were assessed using both smoothed CT slices and attenuation maps.ResultsLAC_511 keV extracted from phantom data are in good correlation with the expected theoretical values, except for the standard 10 mm diameter dense bone insert, where the obtained CTAC values are underestimated. Assuming a sample size issue, similar acquisitions were performed with a special 30 mm-diameter dense bone insert, confirming the underestimation as a consequence of the sample size. This effect, caused partly by a too smooth Gaussian filter of the CT images, could be limited by reducing the strength of the filter. Measurements from patients’ data showed the same underestimation of CAL_511 keV for high-density tissues.ConclusionWe assessed an underestimation of the CTAC obtained-values related to the sample size of the insert. A quality control was developed to this effect.     

Bilan initial d’imagerie de l’adénocarcinome pancréatique : données de la littérature sur la place actuelle de la tomographie par émission de positons au 18F-fluorodéoxyglucose (TEP FDG)

In pancreatic adenocarcinoma, initial imaging is essential to better select patients for surgery. Recent literature analysis of F18-Fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET) in pancreatic adenocarcinoma is summarized in the present article. Performances of FDG PET in the fields of lymph node involvement, metastatic involvement and therapeutic efficacy assessment are described for its correct use in pancreatic adenocarcinoma.     

La tomographie par émission de positons couplée à la tomodensitométrie (TEP–TDM) au 18F-fluoro-désoxy-glucose ([18F]-FDG), avec dilution vésicale dans l’imagerie des tumeurs urothéliales. À propos de quatre cas

This article illustrates, by means of four demonstrative case reports of urothelial carcinomas, the potential role of PET–CT using ¹⁸F-fluoro-desoxy-glucose ([¹⁸F]-FDG) with delayed images after diuretic. These patients were referred to the TEP centre of the University Hospital in Bordeaux for the initial staging of a known bladder cancer or for the characterization of residual mass after radical treatment by surgery and radiotherapy. Analysing recent published results this preliminary study underlines the good performances of forced diuresis for the interpretation of bladder wall and thus enables to assess the potential clinical impact of [¹⁸F]-FDG PET–CT in the staging of urothelial carcinoma.     

Mise au point et validation d’un fantôme spécifique pour assurer le suivi des mesures quantitatives en tomographie par émission de positons

Standardized uptake values (SUV) are widely used in positron emission tomography (PET) to quantify [18F]2-fluoro-2-deoxy-d-glucose (18F-FDG) uptake, particularly in therapeutic follow-up. However, this index depends on many factors, be they methodological or biological, and its use is still a subject of debate. In this context, it is fundamental to establish a regular quality control to ensure quantitative indices constancy. In this perspective, a specific phantom with different size cylinder-shaped inserts was developed. The purpose of this study is to show the sensitivity and the interest of this phantom.MethodsThe phantom sensitivity was studied through SUV and recovery coefficient (RC) measurements. Several data analysis methods based on region of interest definition (ROI) were used. Data were reconstructed using clinical routine algorithms. We studied RC variation using cylinders with relative change of size and uptake (simulating treatment response) for different tumor-to-background activity ratio (TBR). Subsequently, the phantom was tested on another PET scanner.ResultsFor all data analysis methods, a considerable RC variation, of about 50%, was found with cylinder size. Measurement methods based on isocontours showed a strong correlation. This phantom also allowed to measure a relative uptake change which turned out to be independent of the measurement method. Despite calibration of the PET/CT systems, quantification differences of about 20% remained between the two centers studied.ConclusionThe results obtained show the interest of this phantom in the framework of following-up quantitative measurements in a given institution, or of an intercomparison in multicenter studies.     

Intérêt de la tomographie par émission de positons (TEP) au 18FDG dans le suivi des patients traités pour carcinome épidermoïde des voies aérodigestives supérieures (VADS) en rémission clinique

IntroductionPosttreatment follow-up of head and neck squamous cell carcinoma (HNSCC) recurrence is a diagnostic challenge. Tissue distortions from radiation and surgery can obscure early detection of recurrence by conventional follow-up approaches such as physical examination (PE), computed tomography, and magnetic resonance imaging. A number of studies have shown that ¹⁸Fluoro-fluorodeoxyglucose (¹⁸FDG) Positron emission tomography (PET) may be an effective technique for the detection of persistent, recurrent, and distant metastatic HNSCC after treatment. The aim of this prospective study was to determine the benefits (sensitivity, specificity, predictive values, and accuracy) of ¹⁸FDG PET using hybrid PET–Computed tomography system (PET/CT) in the detection of HNSCC subclinical locoregional recurrence and distant metastases, in patients 12 months after curative treatment with a negative conventional follow up.Materials and MethodsNinety-one patients cured from head and neck squamous cell carcinoma (HNSCC) without any clinical element for recurrence were included. Whole-body ¹⁸FDG PET/CT examination was performed 11.6 ± 4.4 months after the end of the treatment. The gold standard was histopathology or 6 months imaging follow-up.ResultsThe whole-body ¹⁸FDG PET/CT of the 91 patients in this study consisted of 52 negative and 39 positive results. Nine of these patients who exhibited abnormal ¹⁸FDG uptake in head and neck area did not have subsequently proven recurrent HNSCC (false positive). Thirty had proven recurrence (true positive). All 52 patients with negative readings of ¹⁸FDG PET/CT remained free of disease at 6 months (true negative). The sensitivity and specificity of ¹⁸FDG PET/CT in this study for the diagnosis of HNSCC recurrence were 100% (30/30) and 85% (52/61) respectively. The positive predictive value was 77% (30/39). The negative predictive value was 100% (52/52). The overall accuracy was 90% (82/91).ConclusionThe results of our study confirm the high effectiveness of ¹⁸FDG PET/CT in assessment of HNSCC recurrence. It suggests that this modality is more accurate than conventional follow-up PE alone in the assessment of patient recurrence after previous curative treatment for HNSCC. Therefore, a PET study could be systematically proposed at 12 months after the end of the treatment.     

Optimisation du traitement de l’ostéome ostéoïde par le repérage isotopique peropératoire: à propos d’un cas

Osteoids osteomas are small-sized benign painful bony tumours. Their complete surgical ablation consists in the proper treatment. The use of a portable Gamma probe allows to accurately localize the osteoid osteoma after radiolabelling and to reduce the size of incision and the bony ablation. We report the case of a patient having benefited from an isotopic intraoperative localization of an osteoid osteoma in the left tibia. Discussion chapter includes a comprehensive review of literature.