Hugo Palmans

• Group Leader at National Physical Laboratory

Objective. In the recent update of the TRS-398 Code of Practice (CoP), Monte Carlo results were incorporated into the derivation of recommended beam quality correction factors for ionisation chambers (IC) in proton beams. While the underlying Monte Carlo simulations implement detailed models only based on the nominal geometries from manufacturer bl...

Internationally, reference dosimetry for clinical proton beams largely follows the guidelines published by the International Atomic Energy Agency (IAEA TRS-398 Rev. 1 (2024). This approach yields a relative standard uncertainty of 1.7% (k = 1) on the absorbed dose to water determined under reference conditions. The new IPEM code of practice present...

Objective. To investigate the impact of the positioning of plane-parallel ionization chambers in proton beams on the calculation of the chamber-specific factor fQ and, hence, the beam quality correction factor kQ,Q0. Approach. Monte Carlo simulations were performed to calculate the chamber-specific factor fQ in monoenergetic proton beams for six di...

Background/Objectives: Spatial fractionation of proton fields as sub-millimeter beamlets to treat cancer has shown better sparing of healthy tissue whilst maintaining the same tumor control. It is critical to ensure primary standard dosimetry is accurate and ready to support the modality’s clinical implementation. Methods: This work provided a proo...

Background Proton beam therapy, when integrated with MRI guidance, presents complex dosimetric challenges due to interactions with magnetic fields. Prior research has emphasized the nuanced impact of magnetic fields on dosimetry. For thermoluminescent dosimeters (TLDs) the electron‐return effect, alongside small air cavities surrounding the pellets...

Objective. In this experimental work we compared the determination of absorbed dose to water using four ionization chambers (ICs), a PTW-34045 Advanced Markus, a PTW-34001 Roos, an IBA-PPC05 and a PTW-30012 Farmer, irradiated under the same conditions in one continuous- and in two pulsed-scanned proton beams. Approach. The ICs were positioned at 2...

Background and purpose Accurate dosimetry in Ultra-High Dose Rate (UHDR) beams is challenging because high levels of ion recombination occur within ionisation chambers used as reference dosimeters. A Small-body Portable Graphite Calorimeter (SPGC) exhibiting a dose-rate independent response was built to offer reduced uncertainty on secondary standa...

The aim of this work is to present the first microdosimetric spectra measured with a miniaturised tissue-equivalent proportional counter in the clinical environment of the MedAustron ion-beam therapy facility. These spectra were gathered with a 62.4-MeV proton beam and have been compared with microdosimetric spectra measured in the 62-MeV clinical...

Objective: To report the use of a portable primary standard level graphite calorimeter for direct dose determination in clinical pencil beam scanning proton beams, which forms part of the recommendations of the proposed Institute of Physics and Engineering in Medicine (IPEM) Code of Practice (CoP) for proton therapy dosimetry. Approach: The Primary...

Background Combining carbon ion therapy with on‐bed MR imaging has the potential to bring particle therapy to a new level of precision. However, the introduction of magnetic fields brings challenges for dosimetry and quality assurance. For protons, a small, but significant change in detector response was shown in the presence of magnetic fields pre...

A new head and neck phantom for proton end-to-end dosimetry audit

Objective: In proton therapy there is a need for proton optimised tissue-equivalent materials as existing phantom materials can produce large uncertainties in the determination of absorbed dose and range measurements. The aim of this work is to develop and characterise optimised tissue-equivalent materials for proton therapy. Approach: A mathema...

Alanine pellets with a nominal thickness of 0.5 mm and diameter of 5 mm were irradiated with monoenergetic x-rays at the Diamond Light Source synchrotron, to quantify their response in the 8 to 20 keV range relative to 60Co radiation. The absorbed dose to graphite was measured with a small portable graphite calorimeter, and the DOSRZnrc code in the...

A paradigm shift is occurring in clinical oncology exploiting the recent discovery that short pulses of ultra-high dose rate (UHDR) radiation—FLASH radiotherapy—can significantly spare healthy tissues whilst still being at least as effective in curing cancer as radiotherapy at conventional dose rates. These properties promise reduced post-treatment...

Introduction: Particle therapy using pencil beam scanning (PBS) faces large uncertain- ties related to ranges and target motion. One possibility to improve existing mitigation strategies is a 2D range modulator (2DRM). A 2DRM offers faster irradiation times by reducing the number of layers and spots needed to create a spread-out Bragg peak. We hav...

In radiotherapy, radiation-quality should be an expression of the biological and physical characteristics of ionizing radiation such as spatial distribution of ionization or energy deposition. Linear energy transfer (LET) and lineal energy (y) are two descriptors used to quantify the radiation quality. These two quantities are connected and exhibit...

Purpose: Reporting on the first implementation of a proton dedicated commercial device (IBA Sphinx/Lynx) for daily Quality Assurance (QA) of scanned proton and carbon ion beams. Methods: Daily QA trendlines over more than 3 years for protons and more than 2 years for carbon ions have been acquired. Key daily QA parameters were reviewed, namely t...

Background and purpose: The Global Clinical Trials RTQA Harmonization Group (GHG) set out to evaluate and prioritize clinical trial quality assurance. Methods: The GHG compiled a list of radiotherapy quality assurance (QA) tests performed for proton and photon therapy clinical trials. These tests were compared between modalities to assess whethe...

Objective: A calibration service based on a primary standard calorimeter for the direct determination of absorbed dose for proton beams does not exist. A new Code of Practice (CoP) for reference dosimetry of proton beams is being developed by a working party of the UK Institute of Physics and Engineering in Medicine (IPEM), which will recommend th...

Purpose To evaluate the dosimetric accuracy for small field proton irradiation relevant for pre-clinical in vivo studies using clinical infrastructure and technology. In this context additional beam collimation and range reduction was implemented. Methods and materials The clinical proton beam line employing pencil beam scanning (PBS) was adapted...

Objective: To review the currently available data on beam quality correction factors, k_Q, for ionization chambers in clinical proton beams and derive their current best estimates for the updated recommendations of the IAEA TRS-398 Code of Practice. Approach: The reviewed data come from 20 publications from which k_Q values can be derived either...

Purpose The purpose of this paper is to compare the response of two different types of solid‐state microdosimeters, that is, silicon and diamond, and their uncertainties. A study of the conversion of silicon microdosimetric spectra to the diamond equivalent for microdosimeters with different geometry of the sensitive volumes is performed, including...

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 (MUs) is introdu...

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...

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...

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...

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...

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...

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 in...

Gomà (2020 Phys. Med. Biol.) commented on our paper ‘Lateral response heterogeneity of Bragg peak ionization chambers for narrow-beam photon and proton dosimetry’ (Kuess et al 2017 Phys. Med. Biol. 62 9189–206) which describes a method to determine the response pattern of large-area ionization chambers using a collimated x-ray beam. Gomà performed...

Purpose To investigate the response of detectors for proton dosimetry in the presence of magnetic fields. Material and Methods Four ionization chambers (ICs), 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 beam...

Purpose This paper presents a novel method for the calculation of three‐dimensional (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...

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...

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...

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 fits. T...

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...

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...

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...

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...

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...

Purpose The dose response of Gafchromic EBT3 films exposed to proton beams depends on the dose, and additionally on the beam quality, which is often quantified with the linear energy transfer (LET) and, hence, also referred to as LET quenching. Fundamentally different methods to determine correction factors for this LET quenching effect have been r...

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...

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...

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...

A new practical method to determine the ion recombination correction factor ( k_s ) 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...

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 dimensio...

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 of i...

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...

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...

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...

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...

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 diff...

Purpose The dose core of a proton pencil beam (PB) is enveloped by a low dose area reaching several centimeters 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 e...

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...

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 accuracy...

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...

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...

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...

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...

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...

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...

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...

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...

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:...

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...