D. Visvikis

Unité Inserm U1077, Caen, Lower Normandy, France

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Publications (259)506.49 Total impact

  • Colloque RITS- Recherche en Imagerie et Technologie pour la Santé, Dourdan, France; 03/2015
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    ABSTRACT: Intra-tumor uptake heterogeneity in (18)F-FDG PET has been associated with patient treatment outcomes in several cancer types. Textural features (TF) analysis is a promising method for its quantification. An open issue associated with the use of TF for the quantification of intratumoral heterogeneity concerns its added contribution and dependence on the metabolically active tumor volume (MATV), which has already been shown as a significant predictive and prognostic parameter. Our objective was to address this question using a larger cohort of patients covering different cancer types. A single database of 555 pre-treatment (18)F-FDG PET images (breast, cervix, esophageal, head & neck and lung cancer tumors) was assembled. Four robust and reproducible TF-derived parameters were considered. The issues associated with the calculation of TF using co-occurrence matrices (such as the quantization and spatial directionality relationships) were also investigated. The relationship between these features and MATV, as well as among the features themselves was investigated using Spearman rank coefficients, for different volume ranges. The complementary prognostic value of MATV and TF was assessed through multivariate Cox analysis in the esophageal and NSCLC cohorts. A large range of MATVs was included in the population considered (3-415 cm(3), mean = 35, median = 19, SD=50). The correlation between MATV and TF varied greatly depending on the MATVs, with reduced correlation for increasing volumes. These findings were reproducible across the different cancer types. The quantization and the calculation method both had an impact on the correlation. Volume and heterogeneity were independent prognostic factors (P = 0.0053 and 0.0093 respectively) along with stage (P = 0.002) in NSCLC, but in the esophageal tumors, volume and heterogeneity had less complementary value due to smaller overall volumes. Our results suggest that heterogeneity quantification and volume may provide valuable complementary information for volumes above 10cm(3), although the complementary information increases substantially with larger volumes. Copyright © 2014 by the Society of Nuclear Medicine and Molecular Imaging, Inc.
    Journal of Nuclear Medicine 12/2014; · 5.56 Impact Factor
  • San Antonio Breast Cancer Symposium; 12/2014
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    ABSTRACT: Optimization of Image-based Dosimetry in Y90 Radioembolization: a Monte Carlo approach using the GATE simulation toolkit. K. Mountris1, A. Autret3, P. Papadimitroulas1, G. Loudos², D. Visvikis3, G. Nikiforidis1 1 Department of Medical Physics, School of Medicine, University of Patras, Rion, GR 265 04 ² Department of Medical Instruments Technology, Technological Educational institute of Athens, Ag. Spyridonos Street, Egaleo GR 122 10, Athens, Greece 3 LaTIM, UMR 1101 INSERM, CHRU Brest, Brest, France Purpose: The ability of Monte Carlo simulation for PET acquisition of Y90 radioembolization and the correlation of image-based dosimetric results derived from the simulated data with respective results derived from the MC simulation of the treatment planning surrogates Tc99m-MAA (macroaggregated albumin) and Ga68-MAA were investigated. Methods: We used the XCAT phantom, using GATE MC platform, since this combination can provide ground truth data. The tiny branch of Y90 internal pair production was modeled (32 ppm) for a 30 minutes PET acquisition. We assumed homogeneous distribution of a 2.5GBq activity in the liver tissue and the tumor with a TNR 3:1 to compare our results with the partition model. The Tc99m-MAA SPECT acquisition simulated assuming homogeneous distribution of 200MBq Tc99m-MAA for 10 min with 64 frames (20s/frame). For pretreatment dosimetry optimization we simulated a Ga68-MAA PET acquisition for the same activity and acquisition time as in the Tc99m-MAA protocol. Comparison was applied between the dosimetric results of Y90-surrogates and the Y90 protocol. We generated 3D dose maps using a kernel-convolution method on the reconstructed images with an onsite generated Y90 kernel. Furthermore the total doses of tumor and normal liver parenchyma were calculated for all the scenarios creating 1D histograms. Results: For the Y90 scenario the liver dose was 62.94Gy, 15.5% higher than the dose calculated with the partition model (54.50Gy) and the tumor dose was 147.28Gy, 9.9% lower than the partition model (163.50Gy). For the Ga68 scenario the liver dose was 65.62Gy and the tumor dose 143.44Gy. For the Tc99m scenario the liver and tumor doses were 70.98Gy and 149.60Gy respectively. In all cases the tumor dose was underestimated relating to the partition model while the normal liver dose was overestimated. The difference between Ga68 derived doses over Y90 was +4.29% for the liver dose and -2.64% for the tumor dose while for the Tc99m acquisition the difference was +12.8% and +1.6% respectively. Conclusion: The Ga68-MAA showed significantly lower dosimetric differences with Y90 than Tc99m-MAA in liver dose calculation. As liver dose estimation is a key limiting factor in the treatment planning, the better correlation of Ga68-MAA can improve the therapeutic results of the treatment. Further investigation in the usage of Ga68-MAA in radioembolization must be done. keywords: yttrium-90, radioembolization, image-based dosimetry, Tc99m-MAA, Ga68-MAA
    8th European Conference on Medical Physics, Athens; 09/2014
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    ABSTRACT: Cardiac imaging suffers from both respiratory and cardiac motion. One of the proposed solutions involves double gated acquisitions. Although such an approach may lead to both respiratory and cardiac motion compensation there are issues associated with (a) the combination of data from cardiac and respiratory motion bins, and (b) poor statistical quality images as a result of using only part of the acquired data. The main objective of this work was to evaluate different schemes of combining binned data in order to identify the best strategy to reconstruct motion free cardiac images from dual gated positron emission tomography (PET) acquisitions.
    Medical Physics 07/2014; 41(7):072504. · 3.01 Impact Factor
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    ABSTRACT: Thirty patients with proven colorectal cancer prospectively underwent integrated 18F-FDG PET/DCE-CT to assess the metabolic-flow phenotype. Both CT blood flow parametric maps and PET images were analyzed. Correlations between PET heterogeneity and perfusion CT were assessed by Spearman's rank correlation analysis.
    PLoS ONE 06/2014; 9(6):e99567. · 3.53 Impact Factor
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    ABSTRACT: The goal of this study was to compare visual assessment of intratumor (18)F-FDG PET uptake distribution with a textural-features (TF) automated quantification and to establish their respective prognostic value in non-small cell lung cancer (NSCLC).
    Journal of Nuclear Medicine 06/2014; 55(8). · 5.56 Impact Factor
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    ABSTRACT: In this paper, the authors' review the applicability of the open-source GATE Monte Carlo simulation platform based on the GEANT4 toolkit for radiation therapy and dosimetry applications. The many applications of GATE for state-of-the-art radiotherapy simulations are described including external beam radiotherapy, brachytherapy, intraoperative radiotherapy, hadrontherapy, molecular radiotherapy, and in vivo dose monitoring. Investigations that have been performed using GEANT4 only are also mentioned to illustrate the potential of GATE. The very practical feature of GATE making it easy to model both a treatment and an imaging acquisition within the same frameworkis emphasized. The computational times associated with several applications are provided to illustrate the practical feasibility of the simulations using current computing facilities.
    Medical Physics 06/2014; 41(6):064301. · 3.01 Impact Factor
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    ABSTRACT: Purpose: The objective of this work is to test the advantage of using the surface acquired by two stereo Time-of-Flight (ToF) cameras in comparison of the use of one camera only for patient positioning in radiotherapy.
    Medical Physics 06/2014; 41(6):199-199. · 3.01 Impact Factor
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    ABSTRACT: Purpose: To evaluate the feasibility of delivering a gated Intensity Modulated Radiotherapy (IMRT) treatment using multiple respiratory phases in order to account for all anatomic changes during free breathing and accelerate the gated treatment without increasing the dose per fraction.
    Medical Physics 06/2014; 41(6):326-326. · 3.01 Impact Factor
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    ABSTRACT: Purpose: The objective of this study was to evaluate the necessity to account for the organs at risk (OARs) respiratory induced motion in addition to the tumor displacement when planning a radiotherapy treatment that accounts for tumor motion.
    Medical Physics 06/2014; 41(6):219-219. · 3.01 Impact Factor
  • 3rd ESTRO Forum, Barcelona, Spain; 04/2014
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    European Journal of Nuclear Medicine 03/2014; · 4.53 Impact Factor
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    ABSTRACT: Background and objective: For many cancer patients who develop vertebral metastases in the natural course of the disease, percutaneous kyphoplasty is a valuable treatment option. By using intraoperative radiotherapy (IORT) with the INTRABEAM™ system during kyphoplasty™, metastases may be sterilized and vertebra stabilized together. This solution results in the reduction of patient discomfort and also restores mobility, which improves the patient quality of life. The aim of our study is to perform a dosimetric evaluation of a Kypho-IORT treatment using the needle applicator to control and validate the doses actually received for such treatment. Method: A simulation of a clinical treatment is performed on an anthropomorphic phantom (RANDO) and dose measurements are collected from thermoluminescent detectors placed on the skin and inside the phantom around the X-ray source. Finally dose calculations are made on the GATE Monte Carlo (MC) platform by integrating computed tomography (CT) images of the phantom with the applicator in place. The validation was performed by comparing simulations and experimental measurements on the phantom. Result: The simulation results show a good fit with the experimental measurements. The average relative differences between experimental measurements and calculated dose rates was lower than 1.5% (Min: 0.2%, Max: 7.5%) and a maximum uncertainty of 0.3% in GATE. Conclusions: This model which has been previously validated in breast cancer can be now considered to be validated for vertebral metastases. The next step will be the validation of the described approach for use in patient dosimetry which should facilitate accounting for the impact of local tissue heterogeneities.
    Translational Cancer research. 01/2014; 3(1):83-87.
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    Tzu-Chen Yen, Dimitris Visvikis, Tinsu Pan, Yu-Hua Dean Fang
    BioMed Research International 01/2014; 2014:930213. · 2.71 Impact Factor
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    ABSTRACT: PET/CT imaging could improve delineation of rectal carcinoma gross tumor volume (GTV) and reduce interobserver variability. The objective of this work was to compare various functional volume delineation algorithms. We enrolled 31 consecutive patients with locally advanced rectal carcinoma. The FDG PET/CT and the high dose CT (CTRT) were performed in the radiation treatment position. For each patient, the anatomical GTVRT was delineated based on the CTRT and compared to six different functional/metabolic GTVPET derived from two automatic segmentation approaches (FLAB and a gradient-based method); a relative threshold (45% of the SUVmax) and an absolute threshold (SUV > 2.5), using two different commercially available software (Philips EBW4 and Segami OASIS). The spatial sizes and shapes of all volumes were compared using the conformity index (CI). All the delineated metabolic tumor volumes (MTVs) were significantly different. The MTVs were as follows (mean ± SD): GTVRT (40.6 ± 31.28ml); FLAB (21.36± 16.34 ml); the gradient-based method (18.97± 16.83ml); OASIS 45% (15.89 ± 12.68 ml); Philips 45% (14.52 ± 10.91 ml); OASIS 2.5 (41.6 2 ± 33.26 ml); Philips 2.5 (40 ± 31.27 ml). CI between these various volumes ranged from 0.40 to 0.90. The mean CI between the different MTVs and the GTVCT was < 0.4. Finally, the DICOM transfer of MTVs led to additional volume variations. In conclusion, we observed large and statistically significant variations in tumor volume delineation according to the segmentation algorithms and the software products. The manipulation of PET/CT images and MTVs, such as the DICOM transfer to the Radiation Oncology Department, induced additional volume variations.
    Journal of applied clinical medical physics / American College of Medical Physics. 01/2014; 15(5):4696.
  • European Society for Radiotherapy and Oncology (ESTRO); 01/2014
  • ESTRO Annual Conference, VIenna; 01/2014
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    ABSTRACT: Radiotherapy of head and neck cancer induces changes in tumour cell proliferation during treatment, which can be depicted by the PET tracer (18)F-fluorothymidine (FLT). In this study, three advanced semiautomatic PET segmentation methods for delineation of the proliferative tumour volume (PV) before and during (chemo)radiotherapy were compared and related to clinical outcome. The study group comprised 46 patients with 48 squamous cell carcinomas of the head and neck, treated with accelerated (chemo)radiotherapy, who underwent FLT PET/CT prior to treatment and in the 2nd and 4th week of therapy. Primary gross tumour volumes were visually delineated on CT images (GTVCT). PVs were visually determined on all PET scans (PVVIS). The following semiautomatic segmentation methods were applied to sequential PET scans: background-subtracted relative-threshold level (PVRTL), a gradient-based method using the watershed transform algorithm and hierarchical clustering analysis (PVW&C), and a fuzzy locally adaptive Bayesian algorithm (PVFLAB). Pretreatment PVVIS correlated best with PVFLAB and GTVCT. Correlations with PVRTL and PVW&C were weaker although statistically significant. During treatment, the PVVIS, PVW&C and PVFLAB significant decreased over time with the steepest decline over time for PVFLAB. Among these advanced segmentation methods, PVFLAB was the most robust in segmenting volumes in the third scan (67 % of tumours as compared to 40 % for PVW&C and 27 % for PVRTL). A decrease in PVFLAB above the median between the pretreatment scan and the scan obtained in the 4th week was associated with better disease-free survival (4 years 90 % versus 53 %). In patients with head and neck cancer, FLAB proved to be the best performing method for segmentation of the PV on repeat FLT PET/CT scans during (chemo)radiotherapy. This may potentially facilitate radiation dose adaptation to changing PV.
    European Journal of Nuclear Medicine 12/2013; · 4.53 Impact Factor
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    ABSTRACT: Aim: PET/CT is widely used for the detection of lymph node involvement in head and neck squamous cell carcinoma (HNSCC). However, PET qualitative and quantitative capabilities are hindered by partial volume effects (PVE). Therefore, a retrospective study on 32 patients (57 lymph nodes) was carried out to evaluate the potential improvement of PVE correction (PVEC) in FDG PET/CT imaging for the diagnosis of HNSCC. Histopathological analysis of lymph nodes following neck dissection was used as the gold standard. Methods: A previously proposed deconvolution based PVEC approach was used to derive improved quantitative accuracy PET images, while the anatomical lymph node volumes were determined on the CT images. Different parameters including SUVmax and SUVmean were derived from both original and PVEC PET images for each patient. Results: Histopathology confirmed that SUVmax and SUVmean after PVEC allows a statistically significant differentiation of malignant and benign lymph nodes (p<0.05). The sensitivity of SUVmax and SUVmean was 64% and 57% respectively with or without PVEC. PVEC increased specificity from 71% to 76% for SUVmax and 57% to 66% for SUVmean. Corresponding accuracy increased from 66% to 71% for SUVmax and from 59% to 66% for SUVmean. However, the most accurate differentiation between benign and malignant nodes was obtained while using the magnitude of SUVmax increase after PVEC with a corresponding sensitivity, specificity and accuracy of 77%, 82% and 80% respectively. Conclusion: Our work shows that the use of partial volume effects correction allows a more accurate nodal staging using FDG PET imaging in HNSCC.
    The quarterly journal of nuclear medicine and molecular imaging: official publication of the Italian Association of Nuclear Medicine (AIMN) [and] the International Association of Radiopharmacology (IAR), [and] Section of the Society of... 12/2013; · 1.72 Impact Factor

Publication Stats

3k Citations
506.49 Total Impact Points


  • 2007–2014
    • Unité Inserm U1077
      Caen, Lower Normandy, France
  • 2004–2014
    • Université de Bretagne Occidentale
      • UMR S1101 - Laboratoire de Traitement de l'Information Médicale - LATIM
      Brest, Brittany, France
  • 2013
    • Aix-Marseille Université
      Marsiglia, Provence-Alpes-Côte d'Azur, France
  • 2003–2013
    • French Institute of Health and Medical Research
      Lutetia Parisorum, Île-de-France, France
    • St George's, University of London
      Londinium, England, United Kingdom
  • 2012
    • CHRU de Strasbourg
      Strasburg, Alsace, France
    • Universität Bern
      Berna, Bern, Switzerland
  • 2011
    • Atomic Energy and Alternative Energies Commission
      Fontenay, Île-de-France, France
  • 2009
    • University of Lyon
      Lyons, Rhône-Alpes, France
  • 2008
    • MRC Clinical Sciences Centre
      London Borough of Harrow, England, United Kingdom
  • 2005–2008
    • Centre Hospitalier Universitaire de Brest
      Brest, Brittany, France
  • 2006
    • ESC Bretagne Brest
      Brest, Brittany, France
    • University of Surrey
      • Department of Physics
      Guilford, England, United Kingdom
  • 2002–2003
    • University College London
      • Institute of Nuclear Medicine
      London, ENG, United Kingdom
  • 2000–2003
    • Middlesex University, UK
      Londinium, England, United Kingdom
  • 2001
    • King's College London
      • Department of Psychological Medicine
      London, ENG, United Kingdom
  • 1999–2000
    • London Research Institute
      Londinium, England, United Kingdom
  • 1998
    • The Royal Marsden NHS Foundation Trust
      • Joint Department of Physics
      Londinium, England, United Kingdom
  • 1995
    • Institute of Cancer Research
      Londinium, England, United Kingdom