Hugo Palmans

Hugo Palmans
National Physical Laboratory | NPL · Medical Physics

About

239
Publications
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3,784
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Publications

Publications (239)
Article
Purpose: Radiochromic films are versatile 2D dosimeters with high resolution and near tissue equivalence. To assure high precision and accuracy, a time-consuming calibration process is required. To improve the time-efficiency, a novel calibration method utilizing the ratio of the same dose profile measured at different monitor units (MU) is introd...
Article
Full-text available
Microdosimetry is increasingly adopted in the characterization of proton and carbon ion beams used in cancer therapy. Spectra and mean values of lineal energy calculated in frequency and dose are seen by many as the tools which, by complementing dosimetric measurements, allow for the most complete characterization of the therapeutic radiation field...
Article
Detailed characterisation of the Roos secondary standard plane-parallel ionisation chamber has been conducted in a novel 200 MeV Very High Energy Electron (VHEE) beam with reference to the standard 12 MeV electron calibration beam used in our experimental work. Stopping-power-ratios and perturbation factors have been determined for both beams and u...
Article
Objective: Experimental determination of beam quality kQ factors for two types of Farmer ionization chambers, NE2571 and IBA FC65-G, in a scanned proton beam for three nominal energies (140 MeV, 180 MeV and 220 MeV) based on water calorimetry. Approach: Beam quality correction factors were determined comparing the results obtained with water cal...
Article
Objective: The boundary crossing algorithm available in Geant4 10.07-p01 general purpose Monte Carlo code has been investigated for a 12 MeV and 200 MeV electron source by the application of a Fano cavity test. Approach: Fano conditions were enforced through all simulations whilst varying individual charged particle transport parameters which contr...
Poster
Full-text available
No ion recombination for ionization chamber (future investigations-before the end of 2012) • For proton beam : recombination for ionization chamber = 0.4% (Palmans et al. (2006)) • No heat transfer between different components of calorimeter (future investigations) • Value for the specific heat capacity of the core : 730 J/kg K (overestimation) (fu...
Article
Full-text available
Purpose: This work presents the validation of an analytical pencil beam dose calculation algorithm in a commercial treatment planning system (TPS) for carbon ions by measurements of dose distributions in heterogeneous phantom geometries. Additionally, a comparison study of carbon ions versus protons is performed considering current best solutions...
Article
Purpose An independent dosimetry audit based on end-to-end testing of the entire chain of radiation therapy delivery is highly recommended to ensure consistent treatments among proton therapy centers. This study presents an auditing methodology developed by the MedAustron Ion Beam Therapy Center (Austria) in collaboration with the National Physical...
Article
Purpose: The aims of this work are to study the response of a small-gap plane-parallel ionization chamber in the presence of charge multiplication and suggest an experimental method to determine the product of the recombination correction factor (ks) and the charge multiplication correction factor (kCM) in order to investigate the latter. Methods...
Article
Purpose: This paper presents a novel method for the calculation of 3D Bragg-Gray water-to-detector stopping power ratio (sw,det ) distributions for proton and carbon ion beams. Methods: Contrary to previously published fluence-based calculations of the stopping power ratio, the sw,det calculation method used in this work is based on the specific...
Article
Full-text available
Purpose: To investigate the response of detectors for proton dosimetry in the presence of magnetic fields. Material & methods: Four ionization chambers, two thimble-type and two plane-parallel-type, and a diamond detector were investigated. All detectors were irradiated with homogeneous single-energy-layer fields, using 252.7 MeV proton beams. A...
Article
The specific advantages of ion beams for application in tumor therapy are attributed to their different macroscopic and microscopic energy deposition pattern as compared to conventional photon radiation. On the macroscopic scale, the dose profile with a Bragg peak at the highest depths and small lateral scattering allow a better conformation of the...
Article
Purpose: The local depth dose gradient and the displacement correction factor for Farmer-type ionization chambers are quantified for reference dosimetry at shallow depth in single-layer scanned proton fields. Method: Integrated radial profiles as a function of depth (IRPDs) measured at three proton therapy centers were smoothed by polynomial fit...
Article
The central Gaussian shaped high dose region of a pencil beam (PB) in light ion beam therapy (LIBT) is enveloped by a low dose region causing non-negligible field size effects and impairs the dose calculation accuracy considerably if the low dose envelope is not well modeled. The purpose of this study was to calculate the practical radius, Rc, at w...
Article
Purpose This paper presents the implementation and comparison of two independent methods of beam monitor calibration in terms of number of particles for scanned proton and carbon ion beams. Methods In the first method, called the single-layer method, dose-area-product to water (DAPw) is derived from the absorbed dose to water determined using a Ro...
Article
A newly-designed large-area plane-parallel ionization chamber (of type PTW 34089), denoted BPC150, with a nominal active volume diameter of 147 mm is characterized in this study. Such chambers exhibit benefits compared to smaller chambers in the field of scanned light-ion beam dosimetry because they capture a larger fraction of the laterally-spread...
Article
4D dose calculation (4D-DC) is crucial for predicting the dosimetric outcome in the presence of intra-fractional organ motion. Time-resolved dosimetry can provide significant insights in 4D pencil beam scanning (PBS) dose accumulation and is therefore irreplaceable for benchmarking 4D-DC. In this study a novel approach of time-resolved dosimetry us...
Article
Purpose To present a reference Monte Carlo (MC) beam model developed in GATE/Geant4 for the MedAustron fixed beam line. The proposed model includes an absolute dose calibration in Dose-Area-Product (DAP) and it has been validated within clinical tolerances for non-isocentric treatments as routinely performed at MedAustron. Material and Methods The...
Article
The monolithic silicon telescope technology allows to produce solid state microdosimeters. A detector constituted by a matrix of pixels (2 μm in thickness) coupled with a deeper stage (about 500 μm in thickness) was designed, developed and characterized by comparing its response against Tissue Equivalent Proportional Counters (TEPCs) in different i...
Article
Full-text available
Purpose: To present an analytical formalism for the in depth assessment of uncertainties of field output factors in small fields related to detector positioning based on dose profile measurements. Additionally, a procedure for the propagation of these uncertainties was developed. Methods: Based on the assumption that one dimensional and two dime...
Article
Full-text available
A new phantom was designed for in vitro studies on cell lines in horizontal particle beams. The phantom enables simultaneous irradiation at multiple positions along the beam path. The main purpose of this study was the detailed dosimetric characterization of the phantom which consists of various heterogeneous structures. The dosimetric measurements...
Article
Purpose: This paper describes the clinical implementation and medical commissioning of the MedAustron Particle Therapy Accelerator (MAPTA) for non-isocentric scanned proton beam treatments. Methods: Medical physics involvement during technical commissioning work is presented. Acceptance testing procedures, including advanced measurement methods...
Article
Anthropomorphic phantoms mimicking organ and tumor motion of patients are essential for end-to-end testing of motion mitigation techniques in ion beam therapy. In this work a commissioning procedure developed with the in-house designed respiratory phantom ARDOS (Advanced Radiation DOSimetry system) is presented. The phantom was tested and benchmark...
Article
This article reviews the development and summarizes the state-of-the-art in absorbed dose calorimetry for all the common clinical beam modalities covered in reference dosimetry codes of practice, as well as for small and nonstandard fields, and brachytherapy. It focuses primarily on work performed in the last ten years by national laboratories and...
Article
Shen (2019) commented on our paper 'Lateral response heterogeneity of Bragg peak ionization chambers for narrow-beam photon and proton dosimetry' regarding the impact of the low dose tail of the collimated x-ray beam we used to acquire individual response maps of large area ionization chambers. The behavior of this low dose tail was measured and co...
Article
A new practical method to determine the ion recombination correction factor ( k<sub>s</sub> ) for plane-parallel and Farmer-type cylindrical chambers in particle beams is investigated. Experimental data were acquired in passively scattered and scanned particle beams and compared with theoretical models developed by Boag and/or Jaffé. The new metho...
Article
This work describes the dosimetric commissioning of the Treatment Planning System (TPS) RayStation v6.1 from RaySearch Laboratories (Stockholm, Sweden) for a synchrotron-based scanned proton beam delivery with isocentric and non-isocentric setups at MedAustron. Focus was on the comparison of the Pencil Beam (PBv4.1) and Monte Carlo (MCv4.0) calcula...
Article
Full-text available
Purpose: Radiochromic film dosimetry is extensively used for quality assurance in photon and proton beam therapy. So far, GafchromicTM EBT3 film appears as a strong candidate to be used in future magnetic resonance (MR) based therapy systems. The response of Gafchromic EBT3 films in the presence of magnetic fields has already been addressed for di...
Article
Full-text available
Purpose: The dose core of a proton pencil beam (PB) is enveloped by a low dose area reaching several cm off the central axis and containing a considerable amount of the dose. Adequate modeling of the different components of the PB profile is therefore required for accurate dose calculation. In this study we experimentally validated one electromagn...
Poster
Full-text available
One major limitation and source of uncertainty in particle therapy is the treatment planning system (TPS) range prediction. This is due to the inherent computed tomography (CT) uncertainties; such as the Hounsfield number to stopping power uncertainties and CT artefacts. Preliminary results show that EBT3 film can be used to measure relative range...
Article
Purpose: In all recent protocols for the reference dosimetry of clinical proton beams ionization chamber perturbation factors are assumed to be unity. In this work, such factors were computed using the FLUKA Monte Carlo code for three ionization chamber types, with particular attention to the influence of nuclear interactions. Methods: The accur...
Article
This article is intended to present the different types of particle and radiation detectors available for applications in particle therapy. Several types of detectors and sensors exist for measurements of absorbed dose in reference and nonreference conditions and the ones in use for beam monitoring. Therefore, this manuscript focuses on the followi...
Article
Purpose: A joint IAEA/AAPM international working group has developed a Code of Practice (CoP) for the dosimetry of small static fields used in external megavoltage photon beam radiotherapy, published by the IAEA as TRS-483. This summary paper introduces and outlines the main aspects of the CoP. Methods: IAEA TRS-483 is a condensation of the wide...
Article
The increased use of complex forms of radiotherapy using small-field photon and proton beams has invoked a growing interest in the use of micro-ionization chambers. In this study, 48 PTW-TM31015 PinPoint-type micro-ionization chambers that are used in the commissioning and patient specific QA of a proton pencil beam scanning (PBS) delivery system h...
Technical Report
Alanine is a suitable dosimeter for absolute dosimetry, dose verification, end-to-end dosimetry and dosimetric audit of clinical proton beams. For establishing traceability to primary standards of absorbed dose to water, NPL's alanine dosimeter is calibrated in a 60Co photon beam. The energy dependence of the alanine response in proton beams has be...
Article
Recently, a new type of radiochromic film, the EBT XD film, has been introduced for high dose radiotherapy. The EBT XD film contains the same structure as the EBT3 film but has a slightly different composition and a thinner active layer. This study benchmarks the EBT XD against EBT3 film for 6 MV and 10 MV photon beams, as well as for 97.4 MeV and...
Article
Full-text available
Background and purpose Conversion factors between dose to medium (Dm,m) and dose to water (Dw,w) provided by treatment planning systems that model the patient as water with variable electron density are currently based on stopping power ratios. In the current paper it will be illustrated that this conversion method is not correct. Materials and me...
Article
This paper describes end-to-end test procedures as the last fundamental step of medical commissioning before starting clinical operation of the MedAustron synchrotron-based pencil beam scanning (PBS) therapy facility with protons. One in-house homogeneous phantom and two anthropomorphic heterogeneous (head and pelvis) phantoms were used for end-to...
Article
Introduction One of the methods of acquiring equipment for a Light Ion Beam Therapy (LIBT) facility is to establish collaboration between the customer and one or more manufacturers, so all parties work towards developing the best equipment for the facility. Following this strategy the specifications for a dual particle synchrotron-based facility in...
Article
Purpose: To describe the implementation of dosimetry equipment and phantoms into clinical practice of light ion beam therapy facilities. This work covers standard dosimetry equipment such as computerized water scanners, films, 2D-array, thimble and plane parallel ionization chambers, but also dosimetry equipment specifically devoted to the pencil...
Article
Large area ionization chambers (LAICs) can be used to measure output factors of narrow beams. Dose area product measurements are proposed an alternative to central-axis point-dose measurements. Using such detectors requires detailed information on the uniformity of the response along the sensitive area. Eight LAICs were investigated in this study:...
Article
Various types of treatment units such as CyberKnife, TomoTherapy and C-arm linear accelerators (LINACs) are operated using flattening filter free (FFF) photon beams. Their reference dosimetry, however, is currently based on codes of practice that provide data which were primarily developed and tested for high-energy photon beams with flattering fil...
Article
Purpose: In this work, the LET-dependence of the response of synthetic diamond detectors is investigated in different particle beams. Method: Measurements were performed in three non-modulated particle beams (proton, carbon and oxygen). The response of five synthetic diamond detectors was compared to the response of a Markus or an Advanced Marku...
Article
Purpose: The IAEA TRS-398 code of practice details the reference conditions for reference dosimetry of proton beams using ionization chambers and the required beam quality correction factors (kQ ). Pencil beam scanning (PBS) systems cannot approximate reference conditions using a single spot. However, dose distributions requested in TRS-398 can be...
Article
Based on international reference dosimetry protocols for light-ion beams, a correction factor ( k<sub>s</sub> ) has to be applied to the response of a plane-parallel ionisation chamber, to account for recombination of negative and positive charges in its air cavity before these charges can be collected on the electrodes. In this work, k<sub>s</sub>...
Poster
Full-text available
With start of patient treatment with protons at MedAustron in 2016, the 6th dual-particle facility worldwide has become operational. From the design our synchrotron-based facility was specified to provide not only protons and carbon ions in general, but proton treatment quality competitive with dedicated proton facilities. Pencil beam scanning for...
Article
Full-text available
The aim of this work was to evaluate the water-equivalence of new trial plastics designed specifically for light-ion beam dosimetry as well as commercially available plastics in clinical proton beams. The water-equivalence of materials was tested by computing a plastic-to-water conversion factor, Hpl,w. Trial materials were characterized experiment...
Article
Full-text available
The aim of this work is to develop and adapt a formalism to determine absorbed dose to water from graphite calorimetry measurements in carbon-ion beams. Fluence correction factors, k <sub>fl</sub>, needed when using a graphite calorimeter to derive dose to water, were determined in a clinical high-energy carbon-ion beam. Measurements were performed...
Article
The high uncertainty in the Relative Biological Effectiveness (RBE) values of particle therapy beam, which are used in combination with the quantity absorbed dose in radiotherapy, together with the increase in the number of particle therapy centres worldwide necessitate a better understating of the biological effect of such modalities.
Article
Introduction The National Physical Laboratory (NPL) proton graphite calorimeter is a primary standard level instrument, capable of determining absorbed dose for proton beam radiotherapy dosimetry in the UK. In order to obtain the absorbed dose from the calorimeter measurement data, various correction factors need to be applied, including the gap co...