Papers by Jacobus Schippers
At PSI, a dedicated proton therapy facility, with a superconducting cyclotron, delivers 250 MeV b... more At PSI, a dedicated proton therapy facility, with a superconducting cyclotron, delivers 250 MeV beam energy, pulsed at 72.85 MHz. The measurement of beam currents (0.1-10 nA) is generally performed by ionisation chambers (ICs), but at the expense of reduced beam quality, and scattering issues. There is a strong demand to have accurate signal with a minimal beam disturbance. A cavity resonator, on fundamental resonance mode, has been built for this purpose. The cavity, coupled to the second harmonic of the pulse rate, provides signals proportional to the beam current. It is installed in a beamline to measure for the energy range 238-70 MeV. Good agreement is reached between the expected and measured sensitivity of the cavity. The cavity delivers information for currents down to 0.15 nA with a resolution of 0.05 nA when integrated over one second. Its application is limited to a machine-safety monitor to trigger interlocks, within the existing domain of the proton therapy due to the low beam current limits. With new advancements in proton therapy, especially FLASH, the cavity resonator's application as an online beam-monitoring device is feasible.
Radiotherapy and Oncology, 2009
Radiotherapy and Oncology, Sep 1, 2007
Medical Physics, May 28, 2008
Physics in Medicine and Biology, Oct 5, 2001
Acta Oncologica, Jul 18, 2011
An increasing number of proton therapy facilities are being planned and built at hospital based c... more An increasing number of proton therapy facilities are being planned and built at hospital based centers. Most facilities are employing traditional dose delivery methods. A second generation of dose application techniques, based on pencil beam scanning, is slowly being introduced into the commercially available proton therapy systems. New developments in accelerator physics are needed to accommodate and fully exploit these new techniques. At the same time new developments such as the development of small cyclotrons, Dielectric Wall Accelerator (DWA) and laser driven systems, aim for smaller, single room treatment units. In general the benefi ts of proton therapy could be exploited optimally when achieving a higher level in accuracy, beam energy, beam intensity, safety and system reliability. In this review an overview of the current developments will be given followed by a discussion of upcoming new technologies and needs, like increase of energy, on-line MRI and proton beam splitting for independent uses of treatment rooms.
Journal of Instrumentation, Sep 1, 2022
At the Paul Scherrer Institute (PSI), the superconducting cyclotron “COMET” delivers a 250 MeV pr... more At the Paul Scherrer Institute (PSI), the superconducting cyclotron “COMET” delivers a 250 MeV proton beam for radiation therapy in pulses of 1ns at the cyclotron-RF frequency of 72.85 MHz. Accurate measurement of the beam position at proton beam currents of 0.1–10 nA in the beam transport line downstream of the degrader is of crucial importance for the treatment safety and quality, beam alignment and feedback systems. This is essential for efficient operation and beam delivery. These measurements are usually performed with intercepting monitors such as ionization chambers (ICs). In this paper, we present a novel non-intercepting position sensitive cavity resonator. The resonant monitor, tuned to the second harmonic of the cyclotron's RF, is based on the detection of the transverse magnetic dipole mode of the EM field generated by the beam. This mode is only excited for off-center beam positions and is measured with the help of four floating cavities within a common grounded cylinder. This paper discusses the BPM fundamental characteristics, design optimization and the underlying parametric investigations involving the contribution of the different modes and crosstalk. We estimate the expected signals from the prototype BPM for position offsets from simulations and compare them with test-bench measurements and beam measurements with the prototype and the improvised BPM design. We conclude by summarizing the achieved position sensitivity, precision, and measurement bandwidth.
In protontherapy fast 3D pencil beam scanning is regarded as the most optimal dose delivery metho... more In protontherapy fast 3D pencil beam scanning is regarded as the most optimal dose delivery method. The requirements to apply this treatment technique and to obtain the maximum possible benefit have a big impact on the accelerator concept. Routinely a very stable, reproducible and adjustable beam intensity is needed, which can be set at a few percent accuracy within a millisecond. Quick changes of maximum intensity from the cyclotron are also needed when changing treatment room. Rescanning the tumour volume at high speed to prevent motion artefacts, needs beam energy variations within 50-80 ms. It will be shown that a cyclotron offers the most advantageous possibilities to achieve this ambitious performance.
Physica Medica, Oct 1, 2020
, a superconducting cyclotron called "COMET" delivers proton beam of 250 MeV pulsed at 72.85 MHz ... more , a superconducting cyclotron called "COMET" delivers proton beam of 250 MeV pulsed at 72.85 MHz for proton radiation therapy. Measuring proton beam currents (0.1-10nA) is of crucial importance for the treatment safety and is usually performed with invasive monitors such as ionisation chambers (ICs) which degrade the beam quality. A new non-invasive beam current monitor working on the principle of electromagnetic resonance is built to replace ICs in order to preserve the beam quality delivered. The fundamental resonance frequency of the resonator is tuned to 145.7 MHz, which is the second harmonic of the pulse rate, so it provides signals proportional to beam current. The cavity resonator installed in the beamline of the COMET is designed to measure beam currents for the energy range 238-70 MeV. Good agreement is reached between expected and measured resonator response over the energy range of interest. The resonator can deliver beam current information down to 0.15 nA for a measurement integration time of 1 s. The cavity resonator might be applied serving as a safety monitor to trigger interlocks within the existing domain of proton radiation therapy. Low beam currents limit the abilities to detect sufficiently, however, with the potential implementation of FLASH proton therapy, the application of cavity resonator as an online beam-monitoring device is feasible.
6th Int. Particle Accelerator Conf. (IPAC'15), Richmond, VA, USA, May 3-8, 2015, Jun 1, 2015
PSI and its Center for Proton Therapy (CPT) is extending its research capabilities in the field o... more PSI and its Center for Proton Therapy (CPT) is extending its research capabilities in the field of proton therapy and pencil beam scanning technology. Gantry 3 will be an additional treatment room at the PROSCAN facility at PSI, Villigen, Switzerland. It will feature a 360 • scanning Gantry delivered by Varian Medical Systems. The Gantry design is based on Varian technology, which will be combined with advanced PSI active scanning technology. The further development of fast energy switching as well as precise spot and continuous line scanning irradiation modes are main research topics at the PROSCAN facility. A major challenge with Gantry 3 is the link of the existing PSI PROSCAN system with the Varian ProBeam system, while retaining the system integrity and high performance level. Additionally, Gantry 3 will be installed and commissioned while keeping the other treatment rooms (Gantry 1, Gantry 2, Optis 2) in full operation. The current development and project status is presented.
Physics in Medicine and Biology, Jun 17, 2003
Predictions of the normal-tissue complication probability (NTCP) for the ranking of treatment pla... more Predictions of the normal-tissue complication probability (NTCP) for the ranking of treatment plans are based on fits of dose-volume models to clinical and/or experimental data. In the literature several different fit methods are used. In this work frequently used methods and techniques to fit NTCP models to dose response data for establishing dose-volume effects, are discussed. The techniques are tested for their usability with dose-volume data and NTCP models. Different methods to estimate the confidence intervals of the model parameters are part of this study. From a critical-volume (CV) model with biologically realistic parameters a primary dataset was generated, serving as the reference for this study and describable by the NTCP model. The CV model was fitted to this dataset. From the resulting parameters and the CV model, 1000 secondary datasets were generated by Monte Carlo simulation. All secondary datasets were fitted to obtain 1000 parameter sets of the CV model. Thus the 'real' spread in fit results due to statistical spreading in the data is obtained and has been compared with estimates of the confidence intervals obtained by different methods applied to the primary dataset. The confidence limits of the parameters of one dataset were estimated using the methods, employing the covariance matrix, the jackknife method and directly from the likelihood landscape. These results were compared with the spread of the parameters, obtained from the secondary parameter sets. For the estimation of confidence intervals on NTCP predictions, three methods were tested. Firstly, propagation of errors using the covariance matrix was used. Secondly, the meaning of the width of a bundle of curves that resulted from parameters that were within the one standard deviation region in the likelihood space was investigated. Thirdly, many parameter sets and their likelihood were used to create a likelihood-weighted probability distribution of the NTCP. It is concluded that for the type of dose response data used here, only a full likelihood analysis will produce reliable results. The often-used approximations, such as the usage of the covariance matrix, produce inconsistent confidence limits on both the parameter sets and the resulting NTCP values.
Seminars in Radiation Oncology, Apr 1, 2018
In recent years there has been increasing interest in the more extensive application of proton th... more In recent years there has been increasing interest in the more extensive application of proton therapy in a clinical and preferably hospital-based environment. However, broader adoption of proton therapy has been hindered by the costs of treatment, which are still much higher than those in advanced photon therapy. This article presents an overview of ongoing technical developments, which have a reduction of the capital investment or operational costs either as a major goal or as a potential outcome. Developments in instrumentation for proton therapy, such as gantries and accelerators, as well as facility layout and efficiency in treatment logistics will be discussed in this context. Some of these developments are indeed expected to reduce the costs. The examples will show, however, that a dramatic cost reduction of proton therapy is not expected in the near future. Although current developments will certainly contribute to a gradual decrease of the treatment costs in the coming years, many steps will still have to be made to achieve a much lower cost per treatment.
International Journal of Radiation Oncology Biology Physics, Feb 1, 2005
Purpose: To study regional differences in radiosensitivity within the rat cervical spinal cord. M... more Purpose: To study regional differences in radiosensitivity within the rat cervical spinal cord. Methods and Materials: Three types of inhomogeneous dose distributions were applied to compare the radiosensitivity of the lateral and central parts of the rat cervical spinal cord. The left lateral half of the spinal cord was irradiated with two grazing proton beams, each with a different penumbra (20 -80% isodoses): lateral wide (penumbra ؍ 1.1 mm) and lateral tight (penumbra ؍ 0.8 mm). In the third experiment, the midline of the cord was irradiated with a narrow proton beam with a penumbra of 0.8 mm. The irradiated spinal cord length (C1-T2) was 20 mm in all experiments. The animals were irradiated with variable single doses of unmodulated protons (150 MeV) with the shoot-through method, whereby the plateau of the depth-dose profile is used rather than the Bragg peak. The endpoint for estimating isoeffective dose (ED 50 ) values was paralysis of fore and/or hind limbs within 210 days after irradiation. Histology of the spinal cords was performed to assess the radiationinduced tissue damage. Results: High-precision proton irradiation of the lateral or the central part of the spinal cord resulted in a shift of dose-response curves to higher dose values compared with the homogeneously irradiated cervical cord to the same 20-mm length. The ED 50 values were 28.9 Gy and 33.4 Gy for the lateral wide and lateral tight irradiations, respectively, and as high as 71.9 Gy for the central beam experiment, compared with 20.4 Gy for the homogeneously irradiated 20-mm length of cervical cord. Histologic analysis of the spinal cords showed that the paralysis was due to white matter necrosis. The radiosensitivity was inhomogeneously distributed across the spinal cord, with a much more radioresistant central white matter (ED 50 ؍ 71.9 Gy) compared with lateral white matter (ED 50 values ؍ 28.9 Gy and 33.4 Gy). The gray matter did not show any noticeable lesions, such as necrosis or hemorrhage, up to 80 Gy. All lesions induced were restricted to white matter structures. Conclusions: The observed large regional differences in radiosensitivity within the rat cervical spinal cord indicate that the lateral white matter is more radiosensitive than the central part of the white matter. The gray matter is highly resistant to radiation: no lesions observable by light microscopy were induced, even after a single dose as high as 80 Gy.
International Journal of Radiation Oncology Biology Physics, Sep 1, 2003
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
8th Int. Particle Accelerator Conf. (IPAC'17), Copenhagen, Denmark, 14â19 May, 2017, May 1, 2017
Paul Scherrer Institute currently extends its PROSCAN facility with a third gantry treatment room... more Paul Scherrer Institute currently extends its PROSCAN facility with a third gantry treatment room-Gantry 3, which is realized in the framework of a research collaboration with Varian Medical Systems (VMS). The main research goals at the PROSCAN facility include further development of precise spot scanning and optimized beam delivery with low dead-time for treatment of moving targets. Consequently Gantry 3 is designed to feature advanced pencil beam scanning technology with a large scan field size of 30 × 40 cm 2 , integrated cone beam CT functionality and will in the future allow fast energy layer switching. The main challenge in realizing Gantry 3 is the integration of the Varian Gantry into the existing PROSCAN control system environment, allowing seamless beam operation. Installation of the additional treatment room has started in summer 2015 followed by the integration and technical commissioning phases of the Gantry in 2016, all during full operation of the existing treatment areas at our facility. We report about the special challenges and achieved performance results during commissioning of the Varian Gantry system in combination with the PSI PROSCAN facility.
Physica Medica, Jul 1, 2020
Since many years proton therapy is an effective treatment solution against deep-seated tumors. A ... more Since many years proton therapy is an effective treatment solution against deep-seated tumors. A precise quantification of sources of uncertainty in each proton therapy aspect (e.g. accelerator, beam lines, patient positioning, treatment planning) is of profound importance to increase the accuracy of the dose delivered to the patient. Together with Monte Carlo techniques, a new research field called Uncertainty Quantification (UQ) has been recently introduced to verify the robustness of the treatment planning. In this work we present the first application of UQ as a method to identify typical errors in the transport lines of a cyclotron-based proton therapy facility and analyze their impact on the properties of the therapeutic beams. We also demonstrate the potential of UQ methods in developing optimized beam optics solutions for high-dimensional problems. Sensitivity analysis and surrogate models offer a fast way to exclude unimportant parameters frcomplex optimization problems such as the design of a superconducting gantry performed at Paul Scherrer Institute in Switzerland. 2. Uncertainty Quantification theory The outcomes of a numerical model are influenced by uncertainties
Physics in Medicine and Biology, Dec 15, 2020
A deeper understanding of biological mechanisms to promote more efficient treatment strategies in... more A deeper understanding of biological mechanisms to promote more efficient treatment strategies in proton therapy demands advances in preclinical radiation research. However this is often limited by insufficient availability of adequate infrastructures for precision image guided small animal proton irradiation. The project SIRMIO aims at filling this gap by developing a portable image-guided research platform for small animal irradiation, to be used at clinical facilities and allowing for a precision similar to a clinical treatment, when scaled down to the small animal size. This work investigates the achievable dosimetric properties of different lowest energy clinical proton therapy beams, manipulated by a dedicated portable beamline including active focusing after initial beam energy degradation and collimation. By measuring the lateral beam size in air close to the beam nozzle exit and the laterally integrated depth dose in water, an analytical beam model based on the beam parameters of the clinical beam at the Rinecker Proton Therapy Center was created for the lowest available clinical beam energy. The same approach was then applied to estimate the lowest energy beam model of different proton therapy facilities, Paul Scherrer Institute, Centre Antoine Lacassagne, Trento Proton Therapy Centre and the Danish Centre for Particle Therapy, based on their available beam commissioning data. This comparison indicated similar beam properties for all investigated sites, with emittance values of a few tens of mm•mrad. Finally, starting from these beam models, we simulated propagation through a novel beamline designed to manipulate the beam energy and size for precise small animal irradiation, and evaluated the resulting dosimetric properties in water. For all investigated initial clinical beams, similar dosimetric results suitable for small animal irradiation were found. This work supports the feasibility of the proposed SIRMIO beamline, promising suitable beam characteristics to allow for precise preclinical irradiation at clinical treatment facilities.
Physical review accelerators and beams, Jun 28, 2018
For an optimal exploitation of the benefits of proton therapy the most accurate dose delivery sys... more For an optimal exploitation of the benefits of proton therapy the most accurate dose delivery system should be used. The TERA Foundation has extensive experience in the field of high gradient high frequency linacs. This paper describes a particular design of a 3 GHz linac boosting the typical cyclotron beams for proton therapy of 230-250 MeV up to 350 MeV. Such an upgrade of a typical proton therapy facility enables performing proton radiography, as well as extending therapeutic capabilities with high energy proton therapy (HEPT). The recent studies and measurements in high-gradient linac technology demonstrated that average fields in the accelerating structures of up to 25-30 MV=m can be achieved, which results in a total linac length of less than 7 m. To test several characteristics of such a linac as a booster of a cyclotron beam, a design has been made of a linac unit accelerating from 250 MeV to 275 MeV, which could be built and inserted for tests in an existing beam line at the PSI proton therapy facility. The feasibility considerations, along with the design of the linac booster and the issues related to a possible integration in an existing cyclotron beam line are detailed in this study.
Modern Physics Letters A, May 14, 2017
The goal of this work is to increase the beam transmission from the cyclotron to the patient loca... more The goal of this work is to increase the beam transmission from the cyclotron to the patient location of ocular tumor treatment facility Optis 2 at the Paul Scherrer Institute and thus to reduce the patient treatment times. The examined options for such transmission increase were the installation of local degraders in the patient treatment room and modification of the energy selection collimator settings. The experiments have shown that an improvement of the beam transmission is possible to achieve, however on a cost of an increase in lateral or distal penumbra of the beam. The benefits and drawbacks of the examined options are discussed.
PSI and its Center for Proton Therapy (CPT) is extending its research capabilities in the field o... more PSI and its Center for Proton Therapy (CPT) is extending its research capabilities in the field of proton therapy and pencil beam scanning technology. Gantry 3 will be an additional treatment room at the PROSCAN facility at PSI, Villigen, Switzerland. It will feature a 360 • scanning Gantry delivered by Varian Medical Systems. The Gantry design is based on Varian technology, which will be combined with advanced PSI active scanning technology. The further development of fast energy switching as well as precise spot and continuous line scanning irradiation modes are main research topics at the PROSCAN facility. A major challenge with Gantry 3 is the link of the existing PSI PROSCAN system with the Varian ProBeam system, while retaining the system integrity and high performance level. Additionally, Gantry 3 will be installed and commissioned while keeping the other treatment rooms (Gantry 1, Gantry 2, Optis 2) in full operation. The current development and project status is presented.
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Papers by Jacobus Schippers