D. Visvikis

Unité Inserm U1077, Caen, Lower Normandy, France

Are you D. Visvikis?

Claim your profile

Publications (267)517.34 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The role of multimodality imaging based on the use of positron emission tomography (PET) coupled to computerised tomography (CT) is continuously gaining ground in the field of oncology. The use of the technique in routine clinical practice is based on a visual interpretation or the determination of parameters such as the maximum standardised uptake value representing the highest activity voxel within the tumor. Other semi-quantitative parameters including the metabolic tumor volume and the total lesion glycolysis are increasingly used in the literature. More recently, alternative image derived parameters characterizing the tumor form and the heterogeneity in the intratumour activity distribution have been proposed. The objective of this article is to cover different aspects on these novel image derived indices, including: (i) the motivation behind their introduction and current use; (ii) obstacles in their utilization; (iii) methodological issues on their definition; (iv) their potential interest for future use in clinical practice.
  • Colloque RITS- Recherche en Imagerie et Technologie pour la Santé, Dourdan, France; 03/2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: Intraoperative radiotherapy (IORT) is continuously gaining ground in cancer treatment. However, there is currently no planning system associated with these devices, which precludes patient-specific dose delivery optimization. The objective of this study was the development and validation of a Monte Carlo simulation (MCS)-based dosimetry platform using the Intrabeam™ system. Methods. After surgical resection of the tumor this system delivers a single dose fraction at the surface of an applicator irradiating the tumor bed through a 50 kV x-ray beam. The GATE MCS platform was used in this study combining the phase space obtained by modeling the x-ray source and the detailed modeling of the additional parts of the Intrabeam™ system. The model was validated by comparing simulated versus experimental measurements of depth dose curves (DDC) and isotropy. A clinical validation study was also carried out using patient computed tomography images. Results. The mean deviation between measured and simulated DDC was 2.9% ± 4.4% and 5.9% ± 5.7% for the bare needle and the use of applicators, respectively. A good agreement with experimental measurements was also found in terms of dose isotropy with a maximum difference of 2.04% for the 40 mm diameter applicator. A patient study revealed a mean absolute deviation of 0.06 Gy between simulated and thermoluminescent dosimeters (TLD) measured skin doses. Conclusion. This study shows the potential of using the GATE MCS platform to model three-dimensional dose distributions of the Intrabeam™ system for use in IORT.
    Acta Oncologica 03/2015; DOI:10.3109/0284186X.2015.1016623 · 3.71 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Respiratory motion is a source of artifacts in multimodality imaging such as PET/MR. Solutions include retrospective or prospective gating. They have however found limited use in clinical practice, since their increased overall acquisition duration to maintain overall image quality. More elaborate methods consist of using 4D MR datasets to extract spatial deformations in order to correct for the respiratory motion in PET. The main drawbacks of such approaches is the relatively long acquisition times associated with 4D MR imaging which is often incompatible with clinical PET/MR protocols. The objective of this work was to overcome these limitations by exploiting a generalized reconstruction by inversion of coupled systems (GRICS) approach. The methodology is based on a joint estimation of motion during the MR image reconstruction process, providing internal structure motion and associated deformation matrices for retrospective use in PET respiratory motion correction. This method was first validated on four MR volunteers and two PET/MR patient datasets by comparing GRICS generated MR images to 4D MR series obtained by retrospective gating. In a second step 4D PET datasets corresponding to acquired 4D MR images were simulated using the GATE Monte Carlo simulation platform. GRICS generated deformation matrices were subsequently used to correct respiratory motion in comparison to the 4D MR image based deformations both for the simulated and the two 4D PET/MR patient datasets. Results confirm that GRICS synchronized MR images correlate well with the acquired 4D MR series. Similarly, the use of GRICS for respiratory motion correction allows an equivalent percentage improvement on lesion contrast, position and size, considering the PET simulated tumors as well as PET real tumors. This work demonstrates the potential interest of using GRICS for PET respiratory motion correction in combined PET/MR using shorter duration acquisitions without the need for 4D MRI and associated specific MR sequences.
    Physics in Medicine and Biology 03/2015; 60(6):2529-2546. DOI:10.1088/0031-9155/60/6/2529 · 2.92 Impact Factor
  • [Show abstract] [Hide abstract]
    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; DOI:10.2967/jnumed.114.144055 · 5.56 Impact Factor
  • San Antonio Breast Cancer Symposium; 12/2014
  • Source
    [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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. DOI:10.1118/1.4881099 · 3.01 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. DOI:10.1371/journal.pone.0099567 · 3.53 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The goal of this study was to compare visual assessment of intratumor F-18-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). Methods: The study retrospectively included 102 consecutive patients. Only primary tumors were considered. Intratumor heterogeneity was visually scored (3-level scale [H-visu]) by 2 nuclear medicine physicians. Tumor volumes were automatically delineated, and heterogeneity was quantified with TF. Mean and maximum standardized uptake value were also included. Visual interobserver agreement and correlations with quantitative assessment were evaluated using the K test and Spearman rank (rho) coefficient, respectively. Association with overall survival and recurrence-free survival was investigated using the Kaplan-Meier method and Cox regression models. Results: Moderate correlations (0.4 < rho < 0.6) between TF parameters and H-visu were observed. lnterobserver agreement for H-visu was moderate (K = 0.64, discrepancies in 27% of the cases). High standardized uptake value, large metabolic volumes, and high heterogeneity according to TF were associated with poorer overall survival and recurrence-free survival and remained an independent prognostic factor of overall survival with respect to clinical variables. Conclusion: Quantification of F-18-FDG uptake heterogeneity in NSCLC through TF was correlated with visual assessment by experts. However, TF also constitutes an objective heterogeneity quantification, with reduced interobserver variability, and independent prognostic value potentially useful for patient stratification and management.
    Journal of Nuclear Medicine 06/2014; 55(8). DOI:10.2967/jnumed.113.133389 · 5.56 Impact Factor
  • Medical Physics 06/2014; 41(6):508-508. DOI:10.1118/1.4889447 · 3.01 Impact Factor
  • [Show abstract] [Hide abstract]
    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. DOI:10.1118/1.4888322 · 3.01 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. DOI:10.1118/1.4871617 · 3.01 Impact Factor
  • [Show abstract] [Hide abstract]
    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. DOI:10.1118/1.4888237 · 3.01 Impact Factor
  • [Show abstract] [Hide abstract]
    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. DOI:10.1118/1.4888769 · 3.01 Impact Factor
  • 3rd ESTRO Forum, Barcelona, Spain; 04/2014
  • Source
    European Journal of Nuclear Medicine 03/2014; 41(6). DOI:10.1007/s00259-014-2748-0 · 4.53 Impact Factor
  • European Society for Radiotherapy and Oncology (ESTRO); 01/2014
  • [Show abstract] [Hide abstract]
    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.
  • Source
    Tzu-Chen Yen, Dimitris Visvikis, Tinsu Pan, Yu-Hua Dean Fang
    BioMed Research International 01/2014; 2014:930213. DOI:10.1155/2014/930213 · 2.71 Impact Factor

Publication Stats

3k Citations
517.34 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
    • Forschungszentrum Jülich
      • Institute of Neurosciences and Medicine (INM)
      Jülich, North Rhine-Westphalia, Germany
    • 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
    • Ontario Institute for Cancer Research
      Toronto, Ontario, Canada
  • 2012
    • CHRU de Strasbourg
      Strasburg, Alsace, France
    • Universität Bern
      Berna, Bern, Switzerland
  • 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
    • Royal Victoria Eye and Ear Hospital
      Dublin, Leinster, Ireland
  • 2000–2003
    • Middlesex University, UK
      Londinium, England, United Kingdom
    • London Research Institute
      Londinium, England, United Kingdom
  • 1999–2002
    • University College London
      • Institute of Nuclear Medicine
      Londinium, England, United Kingdom
  • 2001
    • King's College London
      • Department of Psychological Medicine
      London, ENG, United Kingdom
  • 1998
    • The Royal Marsden NHS Foundation Trust
      • Joint Department of Physics
      Londinium, England, United Kingdom
  • 1995
    • Oxon Epidemiology
      Londinium, England, United Kingdom
    • Institute of Cancer Research
      Londinium, England, United Kingdom