Other articles by Thierry Gevaert on PubMed

• Medical Physics Principles of Radiosurgery Progress in Neurological Surgery. 2007  |   Pubmed ID: 17317975 Beside basic physical notions such as ionizing radiation, beam production and beam characteristics, this chapter will focus on two major principles that should always be considered in a radiosurgery procedure: conformity and selectivity. Those parameters are influenced by different physical beam properties, by the type of beam delivery device and by the way the dose is delivered. Conformity and selectivity should be evaluated for each treatment with the help of some specific indices, i.e. target volume ratio and normal volume ratio based on the dose-volume histograms.
• Treatment Delivery Time Optimization of Respiratory Gated Radiation Therapy by Application of Audio-visual Feedback Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Jun, 2009  |   Pubmed ID: 19368987 The feasibility to use visually guided voluntary breath-hold with and without audio assistance to reduce the total treatment time was evaluated.
• Dosimetric Assessment of Static and Helical TomoTherapy in the Clinical Implementation of Breast Cancer Treatments Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Oct, 2009  |   Pubmed ID: 19682758 Investigation of the use of TomoTherapy and TomoDirect versus conventional radiotherapy for the treatment of post-operative breast carcinoma. This study concentrates on the evaluation of the planning protocol for the TomoTherapy and TomoDirect TPS, dose verification and the implementation of in vivo dosimetry.
• An In-house Developed Resettable MOSFET Dosimeter for Radiotherapy Physics in Medicine and Biology. Feb, 2010  |   Pubmed ID: 20090184 The purpose of this note is to report the feasibility and clinical validation of an in-house developed MOSFET dosimetry system and describe an integrated non-destructive reset procedure. Off-the-shelf MOSFETs are connected to a common PC using an 18 bit/analogue-input and 16 bit/output data acquisition card. A reading algorithm was developed defining the zero-temperature-coefficient point (ZTC) to determine the threshold voltage. A wireless interface was established for ease of use. The reset procedure consists of an internal circuit generating a local heating induced by an electrical current. Sensitivity has been investigated as a function of bias voltage (0-9 V) to the gate. Dosimetric properties have been evaluated for 6 MV and 15 MV clinical photon beams and in vivo benchmarking was performed against thermoluminescence dosimeters (TLD) for conventional treatments (two groups of ten patients for each energy) and total body irradiation (TBI). MOSFETS were pre-irradiated with 20 Gy. Sensitivity of 0.08 mV cGy(-1) can be obtained for 200 cGy irradiations at 5 V bias voltage. Ten consecutive measurements at 200 cGy yield a SD of 2.08 cGy (1.05%). Increasing the dose in steps from 5 cGy to 1000 cGy yields a 1.00 Pearson correlation coefficient and agreement within 2.0%. Dose rate dependence (160-800 cGy min(-1)) was within 2.5%, temperature dependence within 2.0% (25-37 degrees C). A strong angular dependence has been observed for gantry incidences exceeding +/-30 degrees C. Dose response is stable up to 50 Gy (saturation occurs at approximately 90 Gy), which is used as threshold dose before resetting the MOSFET. An average measured-over-calculated dose ratio within 1.05 (SD: 0.04) has been obtained in vivo. TBI midplane-dose assessed by entrance and exit dose measurements agreed within 1.9% with ionization chamber in phantom, and within 1.0% with TLD in vivo. An in-house developed resettable MOSFET-based dosimetry system is proposed. The system has been validated and is currently used for in vivo entrance dose measurement in clinical routine for simple (open field) treatment configurations.
• The Effect of Tomotherapy Imaging Beam Output Instabilities on Dose Calculation Physics in Medicine and Biology. Jun, 2010  |   Pubmed ID: 20442461 A radiotherapy treatment plan is based on an anatomical 'snapshot' of the patient acquired during the preparation stage using a kVCT (kilovolt computed tomography) scanner. Anatomical changes will occur during the treatment course, in some cases requiring a new treatment plan to deliver the prescribed dose. With the introduction of 3D volumetric on-board imaging devices, it became feasible to use the produced images for dose recalculation. However, the use of these on-board imaging devices in clinical routine for the calculation of dose depends on the stability of the images. In this study the validation of tomotherapy MVCT (megavolt computed tomography) produced images, for the purpose of dose recalculation by the Planned Adaptive software, has been performed. To investigate the validity of MVCT images for dose calculation, a treatment plan was created based on kVCT-acquired images of a solid water phantom. During a period of 4 months, MVCT images of the phantom have been acquired and were used by the planned adaptive software to recalculate the initial kVCT-based dose on the MVCT images. The influence of the adapted IVDTs (image value-to-density tables) has been investigated as well as the effect of image acquisition with or without preceding airscan. Output fluctuations and/or instabilities of the imaging beam result in MV images of different quality yielding different results when used for dose calculation. It was shown that the output of the imaging beam is not stable, leading to differences of nearly 3% between the original kV-based dose and the recalculated MV-based dose, for solid water only. MVCT images can be used for dose calculation purposes bearing in mind that the output beam is liable to fluctuations. The acquisition of an IVDT together with the MVCT image set, that is going to be used for dose calculation, is highly recommended.
• Daily Megavoltage Computed Tomography in Lung Cancer Radiotherapy: Correlation Between Volumetric Changes and Local Outcome International Journal of Radiation Oncology, Biology, Physics. Aug, 2011  |   Pubmed ID: 20638192 To assess the predictive or comparative value of volumetric changes, measured on daily megavoltage computed tomography during radiotherapy for lung cancer.
• Prospective, Risk-adapted Strategy of Stereotactic Body Radiotherapy for Early-stage Non-small-cell Lung Cancer: Results of a Phase II Trial International Journal of Radiation Oncology, Biology, Physics. Aug, 2011  |   Pubmed ID: 20708849 Validation of a prospective, risk-adapted strategy for early-stage non-small-cell lung cancer (NSCLC) patients treated with stereotactic body radiotherapy (SBRT).
• Geometric Accuracy of a Novel Gimbals Based Radiation Therapy Tumor Tracking System Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Mar, 2011  |   Pubmed ID: 21316786 VERO is a novel platform for image guided stereotactic body radiotherapy. Orthogonal gimbals hold the linac-MLC assembly allowing real-time moving tumor tracking. This study determines the geometric accuracy of the tracking.
• Single Fraction Versus Fractionated Linac-based Stereotactic Radiotherapy for Vestibular Schwannoma: a Single-institution Experience International Journal of Radiation Oncology, Biology, Physics. Nov, 2011  |   Pubmed ID: 21665381 To evaluate and compare outcomes for patients with vestibular schwannoma (VS) treated in a single institution with linac-based stereotactic radiosurgery (SRS) or by fractionated stereotactic radiotherapy (SRT).
• Gamma Knife, CyberKnife, TomoTherapy: Gadgets or Useful Tools? Current Opinion in Neurology. Dec, 2011  |   Pubmed ID: 22071335 This review provides information and an update on stereotactic radiosurgery (SRS) equipment, with a focus on intracranial lesions and brain neoplasms.
• Setup Accuracy of the Novalis ExacTrac 6DOF System for Frameless Radiosurgery International Journal of Radiation Oncology, Biology, Physics. Apr, 2012  |   Pubmed ID: 21477937 Stereotactic radiosurgery using frame-based positioning is a well-established technique for the treatment of benign and malignant lesions. By contrast, a new trend toward frameless systems using image-guided positioning techniques is gaining mainstream acceptance. This study was designed to measure the detection and positioning accuracy of the ExacTrac/Novalis Body (ET/NB) for rotations and to compare the accuracy of the frameless with the frame-based radiosurgery technique.
• Clinical Evaluation of a Robotic 6-degree of Freedom Treatment Couch for Frameless Radiosurgery International Journal of Radiation Oncology, Biology, Physics. May, 2012  |   Pubmed ID: 21945110 To evaluate the added value of 6-degree of freedom (DOF) patient positioning with a robotic couch compared with 4DOF positioning for intracranial lesions and to estimate the immobilization characteristics of the BrainLAB frameless mask (BrainLAB AG, Feldkirchen, Germany), more specifically, the setup errors and intrafraction motion.
• Phase II Study of Helical Tomotherapy in the Multidisciplinary Treatment of Oligometastatic Colorectal Cancer Radiation Oncology (London, England). 2012  |   Pubmed ID: 22423615 Complete metastasectomy provides a real chance for long-term survival in patients with oligometastatic colorectal cancer (CRC). For inoperable patients, we evaluated in this study intensity-modulated and image-guided radiotherapy (IMRT-IGRT) by helical tomotherapy.
• Computer-aided Analysis of Star Shot Films for High-accuracy Radiation Therapy Treatment Units Physics in Medicine and Biology. May, 2012  |   Pubmed ID: 22538289 As mechanical stability of radiation therapy treatment devices has gone beyond sub-millimeter levels, there is a rising demand for simple yet highly accurate measurement techniques to support the routine quality control of these devices. A combination of using high-resolution radiosensitive film and computer-aided analysis could provide an answer. One generally known technique is the acquisition of star shot films to determine the mechanical stability of rotations of gantries and the therapeutic beam. With computer-aided analysis, mechanical performance can be quantified as a radiation isocenter radius size. In this work, computer-aided analysis of star shot film is further refined by applying an analytical solution for the smallest intersecting circle problem, in contrast to the gradient optimization approaches used until today. An algorithm is presented and subjected to a performance test using two different types of radiosensitive film, the Kodak EDR2 radiographic film and the ISP EBT2 radiochromic film. Artificial star shots with a priori known radiation isocenter size are used to determine the systematic errors introduced by the digitization of the film and the computer analysis. The estimated uncertainty on the isocenter size measurement with the presented technique was 0.04 mm (2σ) and 0.06 mm (2σ) for radiographic and radiochromic films, respectively. As an application of the technique, a study was conducted to compare the mechanical stability of O-ring gantry systems with C-arm-based gantries. In total ten systems of five different institutions were included in this study and star shots were acquired for gantry, collimator, ring, couch rotations and gantry wobble. It was not possible to draw general conclusions about differences in mechanical performance between O-ring and C-arm gantry systems, mainly due to differences in the beam-MLC alignment procedure accuracy. Nevertheless, the best performing O-ring system in this study, a BrainLab/MHI Vero system, and the best performing C-arm system, a Varian Truebeam system, showed comparable mechanical performance: gantry isocenter radius of 0.12 and 0.09 mm, respectively, ring/couch rotation of below 0.10 mm for both systems and a wobble of 0.06 and 0.18 mm, respectively. The methodology described in this work can be used to monitor mechanical performance constancy of high-accuracy treatment devices, with means available in a clinical radiation therapy environment.
• Current Status of Intensified Neo-adjuvant Systemic Therapy in Locally Advanced Rectal Cancer Frontiers in Oncology. 2012  |   Pubmed ID: 22655273 The addition of 5-fluorouracil (5-FU) or its prodrug capecitabine to radiotherapy (RT) is a standard approach in the neo-adjuvant treatment of patients with rectal tumors extending beyond the muscularis propria (stage II) and/or with clinical evidence of regional lymph node metastases (stage III). According to European randomized trials, the combined treatment modality resulted in favorable local control rates as compared with radiotherapy (RT) alone, but no improvement was found regarding the occurrence of distant metastases or overall survival. In an effort to further enhance the response rates and to decrease the high incidence of distant metastases in locally advanced rectal cancer patients, the addition of other chemotherapeutical drugs and biologic agents as radiation sensitizers to neo-adjuvant 5-FU based chemoradiotherapy (CRT) has been recently investigated. The role of those agents is however questionable as first results from phase III data do not show improvement on pathologic complete remission and circumferential resection margin negative resection rates as compared to 5-FU based CRT, nevertheless an increased toxicity.
• Implementation of HybridArc Treatment Technique in Preoperative Radiotherapy of Rectal Cancer: Dose Patterns in Target Lesions and Organs at Risk As Compared to Helical Tomotherapy and RapidArc Radiation Oncology (London, England). 2012  |   Pubmed ID: 22849723 HybridArc is a novel treatment technique blending aperture-enhanced optimized arcs with discrete IMRT-elements, allowing selection of arcs with a set of static IMRT-beams. This study compared this new technique to helical Tomotherapy, and RapidArc, in preoperative radiotherapy of rectal cancer.
• Dosimetric Comparison of Different Treatment Modalities for Stereotactic Radiosurgery of Arteriovenous Malformations and Acoustic Neuromas Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Feb, 2013  |   Pubmed ID: 22884842 We investigated the influence of beam modulation on treatment planning by comparing four available stereotactic radiosurgery (SRS) modalities: Gamma-Knife-Perfexion, Novalis-Tx Dynamic-Conformal-Arc (DCA) and Dynamic-Multileaf-Collimation-Intensity-Modulated-radiotherapy (DMLC-IMRT), and Cyberknife.
• Hepatocytes Determine the Hypoxic Microenvironment and Radiosensitivity of Colorectal Cancer Cells Through Production of Nitric Oxide That Targets Mitochondrial Respiration International Journal of Radiation Oncology, Biology, Physics. Mar, 2013  |   Pubmed ID: 22975619 To determine whether host hepatocytes may reverse hypoxic radioresistance through nitric oxide (NO)-induced oxygen sparing, in a model relevant to colorectal cancer (CRC) liver metastases.
• Initial Assessment of Tumor Tracking with a Gimbaled Linac System in Clinical Circumstances: a Patient Simulation Study Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Feb, 2013  |   Pubmed ID: 23398905 To have an initial assessment of the Vero Dynamic Tracking workflow in clinical circumstances and quantify the performance of the tracking system, a simulation study was set up on 5 lung and liver patients.
• Evaluation of the Clinical Usefulness for Using Verification Images During Frameless Radiosurgery Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Jul, 2013  |   Pubmed ID: 23714654 Our previous studies showed that intrafraction motion needs to be corrected for in frameless radiosurgery. This study was designed to evaluate if verification images can correct for mechanical inaccuracy and intrafraction motion. With proper immobilization and verification images on a regular basis during treatment, mechanical (table-) inaccuracies and intrafraction motion can be corrected for and the absence of PTV-margins warranted.
• A Complementary Dual-modality Verification for Tumor Tracking on a Gimbaled Linac System Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Dec, 2013  |   Pubmed ID: 24238982 For dynamic tracking of moving tumors, robust intra-fraction verification was required, to assure that tumor motion was properly managed during the course of radiotherapy. A dual-modality verification system, consisting of an on-board orthogonal kV and planar MV imaging device, was validated and applied retrospectively to patient data.
• Preoperative Intensity-modulated and Image-guided Radiotherapy with a Simultaneous Integrated Boost in Locally Advanced Rectal Cancer: Report on Late Toxicity and Outcome Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Jan, 2014  |   Pubmed ID: 24239243 The addition of chemotherapy to preoperative radiotherapy has been established as the standard of care for patients with cT3-4 rectal cancer. As an alternative strategy, we explored intensity-modulated and image-guided radiotherapy (IMRT-IGRT) with a simultaneous integrated boost (SIB) in a prospective phase II study. Here, we report outcome and late toxicity after a median follow-up of 54 months.
• Feasibility of Using the Vero SBRT System for Intracranial SRS Journal of Applied Clinical Medical Physics / American College of Medical Physics. 2014  |   Pubmed ID: 24423838 The Vero SBRT system was benchmarked in a planning study against the Novalis SRS system for quality of delivered dose distributions to intracranial lesions and assessing the Vero system's capacity for SRS. A total of 27 patients with one brain lesion treated on the Novalis system, with 3 mm leaf width MLC and C-arm gantry, were replanned for Vero, with a 5 mm leaf width MLC mounted on an O-ring gantry allowing rotations around both the horizontal and vertical axis. The Novalis dynamic conformal arc (DCA) planning included vertex arcs, using 90° couch rotation. These vertex arcs cannot be reproduced with Vero due to the mechanical limitations of the O-ring gantry. Alternative class solutions were investigated for the Vero. Additionally, to distinguish between the effect of MLC leaf width and different beam arrangements on dose distributions, the Vero class solutions were also applied for Novalis. In addition, the added value of noncoplanar IMRT was investigated in this study. Quality of the achieved dose distributions was expressed in the conformity index (CI) and gradient index (GI), and compared using a paired Student's t-test with statistical significance for p-values ≤ 0.05. For lesions larger than 5 cm3, no statistical significant difference in conformity was observed between Vero and Novalis, but for smaller lesions, the dose distributions showed a significantly better conformity for the Novalis (ΔCI = 13.74%, p = 0.0002) mainly due to the smaller MLC leaf width. Using IMRT on Vero reduces this conformity difference to nonsignificant levels. The cutoff for achieving a GI around 3, characterizing a sharp dose falloff outside the target volume was 4 cm3 for Novalis and 7 cm3 for Vero using DCA technique. Using noncoplanar IMRT, this threshold was reduced to 3 cm3 for the Vero system. The smaller MLC and the presence of the vertex fields allow the Novalis system to better conform the dose around the lesion and to obtain steeper dose falloff outside the lesion. Comparable dosimetric characteristics can be achieved with Vero for lesions larger than 3 cm3 and using IMRT.
• Impact of Planning Target Volume Margins and Rectal Distention on Biochemical Failure in Image-guided Radiotherapy of Prostate Cancer Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Apr, 2014  |   Pubmed ID: 24631146 A previous study in our department demonstrated the negative impact on freedom from biochemical failure (FFBF) of using too narrow planning target volume (PTV) margins during prostate image-guided radiotherapy (IGRT). Here, we investigated the impact of appropriate PTV margins and rectal distention on FFBF.
• Treating Patients with Real-time Tumor Tracking Using the Vero Gimbaled Linac System: Implementation and First Review Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Sep, 2014  |   Pubmed ID: 25049177 To report on the first clinical application of a real-time tumor tracking (RTTT) solution based on the Vero SBRT gimbaled linac system for treatment of moving tumors.
• Impact of Inadequate Respiratory Motion Management in SBRT for Oligometastatic Colorectal Cancer Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Nov, 2014  |   Pubmed ID: 25441611 Stereotactic body radiotherapy (SBRT) in oligometastatic colorectal cancer (CRC) resulted in a disappointing 1-year local control rate of 54% in our experience. We aimed to determine the root cause(s).
• Improving the Intra-fraction Update Efficiency of a Correlation Model Used for Internal Motion Estimation During Real-time Tumor Tracking for SBRT Patients: Fast Update or No Update? Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Sep, 2014  |   Pubmed ID: 25443498 For tumor tracking, a correlation model is used to estimate internal tumor position based on external surrogate motion. When patients experience an internal/external surrogate drift, an update of the correlation model is required to continue tumor tracking. In this study, the accuracy of the internal tumor position estimation for both the clinical available update at discrete points in time (rebuild) and an in-house developed non-clinical online update approach was investigated.
• Analysis of the Targeting Uncertainty of a Stereotactic Frameless Radiosurgery Technique for Arteriovenous Malformation Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. Dec, 2014  |   Pubmed ID: 25454170 In order to target arteriovenous malformations (AVM) in a frameless approach, registration of two-dimensional (2D) digital-subtracted-angiographs (DSA) with three-dimensional (3D) computed tomography (CT) is required. Targeting accuracy and delineation of a frameless 2D-DSA and 3D-CT image registration tool based on bony anatomy of the skull was evaluated. This frameless approach assures accurate target localization and can be used in a clinical setting.
• Dosimetric Comparison of Different Treatment Modalities for Stereotactic Radiosurgery of Meningioma Acta Neurochirurgica. Apr, 2015  |   Pubmed ID: 25413163 The objective of this study was to compare the three most prominent systems for stereotactic radiosurgery in terms of dosimetric characteristics: the Cyberknife system, the Gamma Knife Perfexion and the Novalis system.
• Erratum To: Dosimetric Comparison of Different Treatment Modalities for Stereotactic Radiosurgery of Meningioma Acta Neurochirurgica. Apr, 2015  |   Pubmed ID: 25530173
• Quality Assurance of a 50-kV Radiotherapy Unit Using EBT3 GafChromic Film: A Feasibility Study Technology in Cancer Research & Treatment. Jan, 2015  |   Pubmed ID: 25575576 Radiochromic EBT3 film is gaining acceptance as a valuable dosimetry system for high-energy photon beams. The advantages of these films over other dosimetry systems are low spectral sensitivity and high spatial resolution. The aim of this study was to validate EBT3 film as a dosimeter for machine and treatment quality assurance (QA) of a 50-kV radiotherapy unit.
• Geometric Verification of Dynamic Wave Arc Delivery With the Vero System Using Orthogonal X-ray Fluoroscopic Imaging International Journal of Radiation Oncology, Biology, Physics. Mar, 2015  |   Pubmed ID: 25962626 The purpose of this study was to define an independent verification method based on on-board orthogonal fluoroscopy to determine the geometric accuracy of synchronized gantry-ring (G/R) rotations during dynamic wave arc (DWA) delivery available on the Vero system.