Original articleSubstitution of 11C-methionine PET by perfusion MRI during the follow-up of treated high-grade gliomas: Preliminary results in clinical practiceSubstitution du PET-méthionine par la perfusion IRM lors du suivi thérapeutique des gliomes de haut grade : résultats préliminaires en pratique clinique
Introduction
Magnetic resonance imaging (MRI) is nowadays the technique of choice for accurate brain tumour work-up. It is the key modality for characterizing lesion topography and morphology, evaluation of the tumoral extension and plays an important role in the follow-up during treatment. For additional physiological information, morphological MRI can be assisted by complementary MR techniques such as spectroscopy, diffusion weighted imaging and perfusion weighted imaging (PWI); those so called “functional imaging” techniques are a growing necessary step in tumoral work-up [1].
PWI can be used to study the tumour vasculature [2], [3] and pinpoint subsection of a given brain tumour where vascularity and endothelial permeability are more altered [4], [5], being thus a useful tool for tumour characterization and treatment planning [6]; moreover, there is an increasing interest in the use of PWI as an indicator of the tumoral response to therapy [7], [8].
Lately, new treatment protocols, combining fractionated radiotherapy and temozolomide, have increased life expectancy to a survival rate of 26.5% at 2 years [9] against 10% at 6 months when conventional radiotherapy is used alone [10]. As a result, the prevalence and extent of posttreatment necrosis has increased [9], [11], [12], [13] making it difficult to determine if an enhancing posttreatment lesion should be considered as a local tumoral recurrence or necrosis: indeed they share the same MRI signs such as enhancement, mass effect and vasogenic oedema [2], [4], [14], [15]. This MRI lack of specificity has prompted the development of other techniques such as carbon-11 labelled methionine (MET) positron emission tomography (PET), which is an indirect method for highlighting tumour proliferation and micro vessel density [16], [17]. It enables a better tissue characterization and is suited for differentiating residual tumour from necrosis with a specificity and sensibility of 61 and 100%, respectively [9], [17], [18].
Nowadays, in such situation and in clinical practice, the MET-PET, with its low specificity, is nevertheless the reference examination when one must plan the future therapeutic scheme of a given patient where the differential diagnosis between recurrence and necrosis must be made [19]. The present study was thus undertaken to examine whether PWI could replace MET-PET in such clinical situation.
First pass PWI, has the big advantage of being performed during the “anatomical” conventional MRI, reducing therefore the number of imaging sessions and the global cost, a non-negligible advantage for the patient and nowadays health policy [11], [18].
Section snippets
Patients
Twenty-eight patients (16 males and 12 females), with a mean age of 51-years-old (ranging from 25 to 74-years-old) and with a histological proven intraaxial primitive brain tumour were included in this retrospective study.
The study was carried out in compliance with our institutional ethic committee (CE Accred. No. 2008/29/246).
All tumours were high-grade gliomas and precise diagnostic was obtained by surgery or stereotactic biopsy: according to the World Health Organization (WHO) histologic
Number of perfusion included into analysis
Out of the 28 patients, a total a 47 PWI were obtained and analysable. Of those 47 PWI, 14 examinations had to be excluded because not performed with a MET-PET. Finally, 33 combined MR and PET examinations were included for further analysis.
MR and PET combined examination analysis
Of the 33 combined MR and PET studies, 31 matched perfectly: 25 studies were positive in both modalities and six were negative. No false positive (type I error) was observed. Nevertheless, two negative MR perfusion corresponded to two positive MET-PET,
Discussion
In clinical neuro-oncologic imaging, conventional MRI is the cornerstone technique for the follow-up of treated high-grade glioma. The main goal of repeated MR acquisition is to detect, precociously, new abnormal modification in the vicinity of the treated tumour site. Most of high-grade tumoral lesions are characterized by a proliferation of immature blood vessels with breakages in the BBB (Fig. 3) [4], [5], [14], [20] whereas radiotherapy induces an acute transient vasodilatation and
Conflicts of interests
None.
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