Comparaison de la dose efficace en TEP/TDM et en TDM

Hybrid imaging, particularly positron emission tomography (PET) combined with CT has emerged in the field of oncology as a modality of choice. The concomitant realization of a standard CT examination, however, raises the question of the additional dose delivered to the patient. This radiation burden could be avoided by performing a single PET/CT examination with injection of contrast media. To verify the potential dosimetric gain of this strategy, we compared the effective dose associated with each modality in a retrospective cohort of 151 patients, homogeneous in weight and size. The average effective dose for a PET/CT (injection of 5-6 MBq/kg of ¹⁸FDG) was 13.5 mSv, the CT dose representing approximately 80% of the PET dose. In our study, the average effective dose in CT thorax/abdomen/pelvis was 21.4 mSv, 60% higher than the PET/CT effective dose.     

TEP/TDM dans le diagnostic et la stadification des lymphomes

Histological subtypes of lymphomas are important because FDG uptake is much greater in aggressive than in indolent lymphomas and this, results in lower sensitivity of PET for the staging of indolent lymphomas. Staging is especially useful when treatment is changed according to staging. Staging with imaging methods has traditionally been performed using a CT scanner and has been based on the detection of nodal enlargement, an increased number of small nodes and in the presence of extranodal masses. However, CT is limited by its poor sensitivity in the detection of extranodal sites of involvement, in the identification of tumour involvement of normal size lymph nodes and in the differentiation between malignant and inflammatory enlarged lymph nodes. The uptake of FDG detected with PET images reflects metabolic activity rather than the size of the tissue masses, localizing tumoral activity in enlarged and in normal size lymph nodes. In the literature review that compares PET with CT, PET usually indicates more lesions than CT would and PET improves sensitivity without losing specificity. However, the majority of studies report that PET, improves the staging in a relatively limited number of patients (10-20%) and may change treatment in less than 10% of patients. Diagnostic accuracy of PET may improve with the use of hybrid PET/CT systems that combine metabolic and morphological imaging, in the same scanner and without moving the patient. This is a promising technique that will overcome the limitations of both modalities and may enhance diagnostic accuracy in lymphoma patients. This hybrid equipment allows the use of PET/CT with contrast-enhanced full dose CT (a diagnostic CT) instead of carrying out PET and CT on different days.     

Indications et performances de la TEP/TDM au fluorure de sodium (FNA)

18F-NAF PET/CT is a relatively uncommon imaging procedure in France, for which indications are similar to those for bone scan and that shows substantial advantages when compared to it. In this review article, we propose to introduce this poorly known radiotracer, its validated indications, performances and some tips for interpretation that will be illustrated by 6 case reports.     

Intérêt de la TEP/TDM dans le bilan d’extension et le suivi des lésions osseuses du myélome multiple

Multiple myeloma (MM) is a malignant hemopathy characterized by a pathologic proliferation of plasmocyts in bone marrow. Detection of bone lesion is of great importance in initial extension screening and for the follow-up because it has an impact on therapeutic strategy. Plain radiographs do not have a good sensitivity for the detection of such lesions. Magnetic resonance imaging (MRI) is an interesting tool to detect diffuse bone marrow infiltration. We propose, based on the experience of our center and through a comprehensive review of the literature, to present the potential of [¹⁸F]-FDG PET/CT for the detection and the therapeutic strategy of bone lesions in MM.     

Intérêt de la TEP/TDM au FDG dans l’investigation étiologique des syndromes paranéoplasiques

Paraneoplastic syndromes (PNS) represent a rare and heterogeneous group of entities whose clinical symptoms may sometimes antedate the diagnosis of the causative tumor. In the context, the identification of the underlying tumor becomes very important for the patient's functional and sometimes vital prognosis, by allowing an earliest treatment of the tumor. ¹⁸FDG PET/CT has become indispensable in the diagnosis and follow-up of numerous cancers but its role in etiological investigation of isolated paraneoplastic syndromes for the research of an occult tumor is not defined yet. Nevertheless, requests of PET/CT in this indication are frequent in nuclear medicine departments, with an uncertain diagnostic yield. We have listed retrospectively 64 patients, sent to nuclear medicine department of Nancy university hospital between 2004 and 2010 for the research of an occult tumor because of a clinically suspected paraneoplastic syndrome, in order to estimate its diagnostic contribution in this indication. According to our results, ¹⁸FDG PET-CT would be interesting by its negative predictive value concerning the tumoral risk, in keeping with its known sensitivity PET-CT may also present an interest for the diagnosis and the characterization of non-tumoral conditions generating symptoms initially wrongly suspected to be paraneoplastic.     

Évaluation de la TEP au 18F-FDG dans la tuberculose extrapulmonaire : premiers résultats d’une étude pilote observationnelle

Aim

Extrapulmonary tuberculosis treatment is difficult to assess and there is a need for new tools. The aim of this observational pilot study is to evaluate the potential role of 18F-FDG PET/CT in the initial staging and treatment evaluation of extrapulmonary tuberculosis.

Methods

Twenty-eight patients were included between January 2009 and 2010. Twenty-three had a 18F-FDG PET/CT before treatment and/or during and/or after treatment. All patients will be followed for 18 months after the end of treatment. A control group of five patients with previous history of tuberculosis was also included and PET/CT was performed.

Results

Three cases of differential diagnosis were excluded of the study. The initial PET for staging showed additional lesions in 8/10 patients compared to conventional imaging. At the end of treatment, 6/11 patients had a negative PET, and 5/11 patients had a positive PET. PET had a significant clinical impact for 3/10 patients at initial staging (guiding biopsy or increase of planned treatment duration), and for 3/16 during follow up (extend or early interruption of the treatment). All PET scans in the control group were negative.

Conclusion

18F-FDG PET has an excellent sensitivity for the detection of extrapulmonary tuberculosis lesion and excellent negative predictive values. The impact of initial PET staging seems significant. The interest of 18F-FDG PET for the evaluation of response to treatment remains to be assessed and will be correlated with patients’ follow up in a second phase of this study.     

Cancer de la prostate : utilité de la TEP-TDM à la F-fluorocholine

In oncology, positron emission computed tomography (PET/CT) has become an essential tool for initial staging, response evaluation and follow-up of cancer patients. Most of the frequent tumors (lung, breast, esophagus, and lymphomas) are highly avid for ¹⁸F-fluorodeoxyglucose (¹⁸FDG), but prostate cancer has not demonstrated significant uptake of FDG. The development of new tracers labeled with ¹⁸F such as choline analogs allowed already to obtain interesting results particularly in patients with biological relapse and inconclusive conventional imaging work-up. The impact of ¹⁸F-flurocholine PET/CT on patient management needs to be validated in large studies, but many centers use already this examination in order to guide further management, including radiotherapy planning.     

Technique du ganglion sentinelle dans le cancer de la prostate

Urological interest of sentinel lymph node procedure in prostate cancer, and methods, both are presented in conformity with the presentation of action concertée en medecine nucléaire (ACOMEN).     

Imagerie hybride dans l’embolie pulmonaire aiguë : apport de la TDM couplée à la tomoscintigraphie de ventilation et de perfusion

Purpose

V/P-SPECT lung scan can be combined with computerized tomography (CT) from hybrid camera. We investigated if CT data could be use only with perfusion scans for the diagnosis of acute pulmonary embolism (PE).

Patients and methods

In a retrospective study, 75 consecutives patients, referred for suspicion of PE, underwent SPECT ventilation and perfusion scans coupled with a CT on Symbia T2. The perfusion images (P-SPECT) were classified as normal or abnormal with systematized (segmental and sub-segmental) or not systematized perfusion abnormalities. The ventilation images (V-SPECT) were considered as normal or abnormal in light of perfusion defects. The same was done for CT images. Correlations between V-SPECT and CT were studied.

Results

Hence, 28 patients had a normal P-SPECT and did not have PE. Patients (47) had an abnormal P-SPECT (among them, 16 turned out to have PE and 31 did not). There were 192 perfusion abnormalities of which 81 were segmental and 81 sub-segmental. Corresponding to these abnormalities, V-SPECT and CT were concordant in 83 % of the cases. When not-concordant, V-SPECT abnormalities with normal CT were found in 14 % of the cases and CT abnormalities with normal V-SPECT were found in 3 % of the cases. According to the EANM guidelines for PE diagnosis, sensitivity was 88 % and specificity 93 % with V/P-SPECT and 100 % and 83 % respectively with CT/P-SPECT (p = NS).

Conclusion

V/P-SPECT remains slightly more specific for the diagnosis of PE. However, this study demonstrates that CT/P-SPECT obtained with hybrid camera could be used for PE diagnosis with performances similar to V/P-SPECT. If these results would be confirmed on larger populations, this could lead to a significant reduction of scanning time which would improve patient comfort and reduce the camera load.     

Valeur pronostique de la TEP au F-FDG dans le bilan d’extension initial du cancer de l’œsophage traité par radiochimiothérapie exclusive

The aim of this retrospective study was to investigate the prognostic significance of initial FDG-PET in patients with newly diagnosed oesophageal carcinoma before exclusive radiochemotherapy. FDG-PET was performed in 29 patients with newly diagnosed oesophageal carcinoma before radiochemotherapy. Maximum standardized uptake value (SUV_max) was determined in each primary lesion and the presence of one or more PET-positive lymph nodes was recorded. Primary tumour volume and tumour length were assessed using two different thresholds for tumour delimitation: SUV = 2.5 and SUV = 40% of SUV_max. Patients were followed clinically during at least 1 year after initial FDG-PET. The median follow-up was 35 months (IC 95% = 26-41 months). Thirteen patients (45%) died during the follow-up. By univariate logistic regression analysis, the SUV_max of primary tumour and the presence of one or more positive lymph nodes were significantly associated with the overall survival. In contrast, no significant difference of prognosis was observed concerning age, sex, tumour cell type, primary site, clinical stage, primary tumour volume and length. Multivariate analysis was not performed due to the too small number of events. FDG-PET provides early prognostic informations in oesophageal carcinoma treated by radiochemotherapy.     

Valeur pronostique du curage ganglionnaire prophylactique dans le cancer différencié de la thyroïde

Objective

Although the efficacy of total thyroidectomy as the first step in differentiated thyroid cancer (DTC) management is well proven, it is always a matter of controversy whether prophylactic lymph node dissection improves prognosis and survival in DTC patients without suspicion of lymph node metastases either clinically or radiologically. The aim of this work is to study relapse rates in patients according to the initial presentation and type of surgery performed, in order to analyze the prognostic impact of lymph node dissection.

Patients and methods

One hundred and thirty patients with DTC were classified according to clinical presentation and type of surgery performed. They were monitored for six years to watch for recurrence.

Results

In patients with no clinical evident lymph nodes, the relapse rate was lower among patients who underwent total thyroidectomy in one step with prophylactic lymph node dissection.

Conclusion

Based on the results of other studies, and on our department experience of thyroid cancer management and monitoring, we strongly advocate careful and systematic exploration of the central lymph node compartments with exploration of the lateral side of the lesion if in doubt.     

Apport de l’imagerie hybride TEMP/TDM dans la détection des ganglions sentinelles : à propos de 32 cas

Objectives

Retrospective evaluation of the SPECT/CT role in the Sentinel Lymph Node identification.

Patients and methods

Thirty-two patients underwent a lymphoscintigraphy with SPECT/CT imaging. Those patients presented several cancer types (16 melanoma, one squamous cell carcinoma, three breast cancers, eight vulvar cancers, three cervical cancers).

Results

The scintigraphic detection rate was 81% with planar imaging while this rate was 89% with SPECT/CT. The SPECT/CT provided an additional quantitative information in 66% cases. Moreover, the quality of the interpretation was better in two different conditions (planar interpretation followed by routine and blinded SPECT/CT interpretation) with SPECT/CT. In our study, the false negative rate is 4.5%.

Conclusions

SPECT/CT provides quantitative and qualitative informations in the sentinel lymph node detection. Therefore, it can be a valuable tool for the surgeon to find and harvest the sentinel lymph node especially where the lymphatic drainage pattern can be unusual or hard to predict (cervical or trunk localisation). It's a new tool for preoperative detection and it can decrease the false negative rate.     

TEP/TDM au FDG et bilan initial des lymphomes : du diagnostic au pronostic

Lymphoma represents a very heterogeneous pathologic disease group and its initial assessment, treatment strategy and prognosis is closely related within each histological subtype. The diagnosis of lymphoma disease is often due to the development of a tumour mass at a lymph node area, or within an organ with or without systemic symptoms. However, all these signs remain non specific. Biopsy is the only reliable diagnostic tool, which can be carried out surgically or guided by the morphological and functional imaging. Once the histological diagnosis is determined by the WHO classification, the staging procedure aim is to provide the prognosis to assist the therapeutic decision. Morphologic imaging primarily based on CT remains the reference in exploring most cases. But in the last decade, the introduction of functional imaging using FDG-PET/CT has dramatically changed the therapeutic management of lymphoma. The additional clinical value provided by initial FDG-PET/CT could lead to an alteration of the therapeutic strategy, as well as to the optimization of radiation therapy or to the establishment of prognostic score and lead to improved lymphoma patient survival in the future.     

Cancer de prostate métastatique résistant à la castration : le point de vue de l’oncologue médical

Most of patient suffering from a prostate cancer will develop a castration resistance. In this common and clinically challenging situation, chemotherapy was not considered very useful until mid 2000s. Docetaxel is now recognized as a standard of care, improving overall survival and quality of life. However, new drugs are needed. Two compounds (cabazitaxel and abiraterone) are now underway to official registration and an autologous vaccin strategy (Sipuleucel) demonstrated a benefit in survival. Based on a greater knowledge of biology, many other agents are currently under development, such as new specific peripheral anti-androgens, anti-angiogenic therapies, or proteasome inhibitors. All these new drugs are promising and may provide more efficient therapies against this incurable disease in the near future.     

Impact d’une méthode originale de synchronisation respiratoire sur la détection des lésions hépatiques en TEP/TDM au F-FDG

In ¹⁸F-Fluoro-Desoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT), respiratory motion induces bias in image interpretations. These movements can introduce organs misregistration between both modalities yielding erroneous attenuation correction and thus wrong maximum standardized uptake values (SUV_max). We present here the results of a clinical study which aims to assess the benefits of a novel respiratory gating method (CT-based) for liver lesions detection. Forty-nine patients planed to undergo hepatic surgery were addressed to our department for PET/CT examination before surgery. Each patient had both standard and CT-based protocols. Hepatic lesions described by two observers on PET images were compared with pathological analysis and intra-operative ultrasound. Sensitivities calculated for observer 1 were 60 and 64% for standard and CT-based, respectively. For the second observer, sensitivities were 58.7 and 72%. CT-based showed a significant increase (P < 0.01) of sensitivity on a per-lesion basis for one observer. CT-based did not improve inter-observer variability. At last, SUV_max were significantly higher with CT-based method (P < 0.001). Respiratory gating CT-based method is easily bearable by the patients. This procedure ensures good matching between both modalities and reduces motion-blurring effect in PET data. CT-based method improves liver lesions detectability and allows more accurate quantitation compared to non-gated FDG-PET/CT examinations.     

Segmentation d’images synchronisées à la respiration en TEP/TDM : étude sur fantôme

The aim of this study is to evaluate the accuracy of segmentation method by adaptive threshold in gated respiratory PET/CT and to deduce their indications and limits. Different acquisitions with phantom allow to study effect of movement, size and tumor activity compared to environment. The validity domain of these techniques, based on optimal threshold, is accurate if the tumor size is superior to 17 mm and the amplitude in a cycle is inferior or equal to 7.5 mm. For patient exams, an acquisition synchronized allows, even in the worst case, to freeze enough displacement in a cycle in which the relative amplitude is the lowest. Threshold adaptive method are validated for gated acquisitions for homogeneous tumors and not subjected to partial volume effect. If tumor size is inferior to three times the spatial resolution of the system, a more complex approach has to be employed.