Other articles by Kenneth Poels on PubMed

• 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.
• 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.
• 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.
• 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.
• 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.
• Fiducial Marker and Marker-less Soft-tissue Detection Using Fast MV Fluoroscopy on a New Generation EPID: Investigating the Influence of Pulsing Artifacts and Artifact Suppression Techniques Medical Physics. Oct, 2014  |   Pubmed ID: 25281963 Because frame rates on current clinical available electronic portal imaging devices (EPID's) are limited to 7.5 Hz, a new commercially available PerkinElmer EPID (XRD 1642 AP19) with a maximum frame rate of 30 Hz and a new scintillator (Kyokko PI200) with improved sensitivity (light output) for megavolt (MV) irradiation was evaluated. In this work, the influence of MV pulse artifacts and pulsing artifact suppression techniques on fiducial marker and marker-less detection of a lung lesion was investigated, because target localization is an important component of uncertainty in geometrical verification of real-time tumor tracking.
• 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.
• 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.
• A Multi-centre Analysis of Treatment Procedures and Error Components in Dynamic Tumour Tracking Radiotherapy Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. May, 2015  |   Pubmed ID: 25998806 This study aimed to compare procedures for dynamic tumour tracking (DTT) using a gimbal-mounted linac between centres in Japan (KU-IBRI) and Belgium (UZB), to quantify tracking error (TE), and to estimate tumour-fiducial uncertainties and PTV margins.
• A Comparison of Two Clinical Correlation Models Used for Real-time Tumor Tracking of Semi-periodic Motion: A Focus on Geometrical Accuracy in Lung and Liver Cancer Patients Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology. May, 2015  |   Pubmed ID: 25981054 A head-to-head comparison of two clinical correlation models with a focus on geometrical accuracy for internal tumor motion estimation during real-time tumor tracking (RTTT).
• 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.