Proton Beam Characteristics Research Articles

Characterization of laser-driven proton beams from near-critical density targets using copper activation

Copper activation was used to characterize high-energy proton beam acceleration from near-critical density plasma targets. An enhancement was observed when decreasing the target density, which is indicative for an increased laser-accelerated hot electron density at the rear target-vacuum boundary. This is due to channel formation and collimation of the hot electrons inside the target. Particle-in-cell simulations support the experimental observations and show the correlation between channel depth and longitudinal electric field strength is directly correlated with the proton acceleration.

MO‐A‐18C‐01: Proton Therapy I: Basics of Proton Therapy

The goal of this session is to introduce the audience to the physics, dosimetry and treatment planning procedures used in proton therapy. The course material covers the basic physics of proton interaction with matter and physical characteristics of clinical proton beams. It will provide information on proton delivery systems and beam delivery techniques for scattered and scanning proton beams. It will include the requirements for dosimetry measurements and present the equipment needed for commissioning of proton beams for clinical use and quality assurance checks as well as methods used for proton beam calibration and dose verification of patient treatment fields. The session covers the treatment planning strategies for various anatomical sites, methods to address uncertainties in proton therapy and uncertainty mitigation to generate robust treatment plans. Challenges involved in the motion management in proton therapy will also be discussed.Learning Objectives: Gain knowledge on physics, dosimetry, treatment planning and quality assurance for proton therapy. Understand the uncertainties associated with proton therapy and currently used strategies for their mitigation in treatment planning.

SU‐E‐T‐239: Monte Carlo Modelling of SMC Proton Nozzles Using TOPAS

Purpose:To expedite and cross‐check the commissioning of the proton therapy nozzles at Samsung Medical Center using TOPAS.Methods:We have two different types of nozzles at Samsung Medical Center (SMC), a multi‐purpose nozzle and a pencil beam scanning dedicated nozzle. Both nozzles have been modelled in Monte Carlo simulation by using TOPAS based on the vendor‐provided geometry. The multi‐purpose nozzle is mainly composed of wobbling magnets, scatterers, ridge filters and multi‐leaf collimators (MLC). Including patient specific apertures and compensators, all the parts of the nozzle have been implemented in TOPAS following the geometry information from the vendor. The dedicated scanning nozzle has a simpler structure than the multi‐purpose nozzle with a vacuum pipe at the down stream of the nozzle.A simple water tank volume has been implemented to measure the dosimetric characteristics of proton beams from the nozzles.Results:We have simulated the two proton beam nozzles at SMC. Two different ridge filters have been tested for the spread‐out Bragg peak (SOBP) generation of wobbling mode in the multi‐purpose nozzle. The spot sizes and lateral penumbra in two nozzles have been simulated and analyzed using a double Gaussian model. Using parallel geometry, both the depth dose curve and dose profile have been measured simultaneously.Conclusion:The proton therapy nozzles at SMC have been successfully modelled in Monte Carlo simulation using TOPAS. We will perform a validation with measured base data and then use the MC simulation to interpolate/extrapolate the measured data. We believe it will expedite the commissioning process of the proton therapy nozzles at SMC.

An Integrated Image Guided Proton Therapy Monitoring System With Real-Time Imaging Processing and Treatment Intervention

Proton therapy is affected greatly by patient breathing motion due to special proton beam characteristics. Real time image guided proton therapy (IGPT) is highly desirable for motion management. An innovative IGRT system is developed to track and predict tumor motion based on hybrid internal/external marker information during proton therapy.

Physics Controversies in Proton Therapy

The physical characteristics of proton beams are appealing for cancer therapy. The rapid increase in operational and planned proton therapy facilities may suggest that this technology is a "plug-and-play" valuable addition to the arsenal of the radiation oncologist and medical physicist. In reality, the technology is still evolving, so planning and delivery of proton therapy in patients face many practical challenges. This review article discusses the current status of proton therapy treatment planning and delivery techniques, indicates current limitations in dealing with range uncertainties, and proposes possible developments for proton therapy and supplementary technology to try to realize the actual potential of proton therapy.

A novel daily QA system for proton therapy

We describe the design and use of a daily quality assurance (QA) system for proton therapy. The QA system is designed to check the overall readiness of proton therapy system consistently within certain reference tolerances by a home‐made QA device (the QA device). The QA device is comprised of a commercially available QA device, rf‐Daily QA 3, a home‐made acrylic phantom, a set of acrylic compensators with various thicknesses, and a mechanical indexing jig. The indexing jig indexes the rf‐Daily QA 3, as well as the acrylic phantom, onto the patient treatment couch. Embedded fiducial markers in the acrylic phantom are used to check X‐ray image quality and positioning alignment accuracy of the imaging system. The rf‐Daily QA 3 is used to check proton beam output, range and symmetry with one single beam delivery. We developed in‐house software to calculate beam range and symmetry, based on various ion chambers' readings inside the rf‐Daily QA 3. With a single setup and one beam irradiation, the QA system is employed to check couch movement, laser alignment, image registration, and reference proton beam characteristics. The simplicity and robustness of this QA system allows for a total QA time of less than 20 minutes per room. The system has been in use at three proton therapy centers since June 2009.PACS numbers: 87.55.Qr, 87.53.Bn

Effect of inside diameter of tip on proton beam produced by intense laser pulse on double-layer cone targets

AbstractThe laser-driven acceleration of proton beams from a double-layer cone target, comprised of a cone shaped high-Z material target with a low density proton layer, is investigated via two-dimensional fully relativistic electro-magnetic particle-in-cell simulations. The dependence of the inside diameter (ID) of the tip size of a double-layer cone target on proton beam characteristics is demonstrated. Our results show that the peak energy of proton beams significantly increases and the divergence angle decreases with decreasing ID size. This can be explained by the combined effects of a stronger laser field that is focused inside the cone target and a larger laser interaction area by reducing the ID size.

Characterization of Uniform Scanning Proton Beams With Proton Loss Model

Characterization of Uniform Scanning Proton Beams With Proton Loss Model

Analysis of laser-generated plasma ionizing radiation by synthetic single crystal diamond detectors

Diamond based detectors have been used in order to analyze the ionizing radiation emitted from the laser-generated plasma. High energy proton/ion beams were generated at Prague Asterix Laser System (PALS) Centre by the sub-nanosecond kJ-class laser at intensities above 1016W/cm2.The tested detectors consisted of a photoconductive device based on high quality chemical vapor deposition (CVD) single crystal diamond, produced at Rome “Tor Vergata” University. They have been operated in planar configuration, having inter-digitized electrodes.The proposed diamond detectors were able to measure UV, X-rays, electrons and ions. They have been employed in time-of-flight (TOF) configuration and their reliability was checked by comparison with standard ion collectors (mostly used at PALS). Both the forward and backward expanding plasma was characterized in the experiment. The results indicate that diamond detectors are very promising for the characterization of fast proton and ion beams produced by high power laser systems.

Chromatic energy filter and characterization of laser-accelerated proton beams for particle therapy

The application of laser accelerated protons or ions for particle therapy has to cope with relatively large energy and angular spreads as well as possibly significant random fluctuations. We suggest a method for combined focusing and energy selection, which is an effective alternative to the commonly considered dispersive energy selection by magnetic dipoles. Our method is based on the chromatic effect of a magnetic solenoid (or any other energy dependent focusing device) in combination with an aperture to select a certain energy width defined by the aperture radius. It is applied to an initial 6D phase space distribution of protons following the simulation output from a Radiation Pressure Acceleration model. Analytical formula for the selection aperture and chromatic emittance are confirmed by simulation results using the TRACEWIN code. The energy selection is supported by properly placed scattering targets to remove the imprint of the chromatic effect on the beam and to enable well-controlled and shot-to-shot reproducible energy and transverse density profiles.

The effect of the proton layer initial size on the proton beam characteristic in target normal sheath acceleration

The proton beam accelerated by the interaction of laser with plasma has practical applications in radiography of dense plasma, fast ignition in inertial confinement fusion, and cancer treatment. The application domain is determined by the characteristic of the proton beams, which is affected by a lot parameters. In order to investigate the effect of the initial size of the proton layer, the two-dimensional Particle-In-Cell (2D-PIC) code Flips2D is used. The total energy of proton beam vs. time is studied, and the relation between the duration of acceleration and the period of laser pulse is obtained. The effects of the proton layer initial width and thickness on the divergence angle and the energy spectrum of the proton beam are investigated. The relation between the proton beam characteristics and proton layer initial size is obtained.

SU‐E‐T‐10: A Computational Model for the Estimation of Biological Dose in a Clinical Proton Beam

Purpose: The variability of relative biological effectiveness (RBE) of a proton beam with spatial distribution is well known. It is dependent on the proton beam characteristics, type of tissue and biological indices. A computational model based on a proton spectrum and LET is used for the estimation of the biological dose. Methods: The depth dose curve of the pristine beam is divided into two regions: the proximal region from the surface to the Bragg peak and the distal region beyond the peak. Knowing the beam energy at the surface in the proximal region, and using the published energy‐range tables, we estimated the effective proton energy at any depth proximal to the Bragg peak. Based on the energy, the LET and RBE is estimated. In the distal region, we assume that the effective beam energy changes monotonically from the value calculated at the peak to the final energy of about 3MeV at the 3% dose level on the distal edge. Applying the calculated RBE factor to the measured depth dose profile we obtain the biological dose in the pristine beam. The method can easily be applied to modulated beams. Results: Our computation model shows that it is possible to predict the biological dose for any combination of beam energy, and for SOBP size based on the available RBE data. Our results showed that the biological dose for a SOBP has finite slope rising to higher values close to distal edge of the peak. Conclusions: A computational model provides an unique tool to estimate the biological dose in any combination of beam energy and SOBP size. If the RBE vs LET data for a tissue is know our computational approach could provide the biological dose accurately in a clinical beam.

Enhancement of ion generation in low-contrast laser-foil interactions by defocusing

The characteristics of proton beams generated from ultra-intense laser-foil interactions under varied focal offsets are experimentally studied on XL-Ⅱ laser facility.The experimental results show that when strong femtosecond prepulses are presented before the main pulse, the conversion efficiency from the laser energy to the protons is enhanced by 3 orders of magnitude with effective improvement of the beam collimation by properly defocusing the laser pulses. The depression of the prepulse effect on the proton acceleration is believed to be one of the main reasons for the significant optimization. Besides, the particle-in-cell (PIC) simulation results indicate that the population of moderate energy electrons increases under large focal offsets, which in turn effectively improves the acceleration electric field and the beam quality.

In Vivo Radiobiological Characterization of Proton Beam at the National Cancer Center in Korea: Effect of the Chk2 Mutation

The relative biological effectiveness (RBE) in the presence or absence of CHK2 was estimated at the Korean National Cancer Center Proton Therapy Center (NCCPTC). The proton beam was fixed at 210 MeV with 6-cm spread-out Bragg peaks (SOBPs) because this is expected to be the most frequently used clinical setting. X-rays were obtained using a 6-MV conventional linear accelerator. The RBE was estimated from the survival of jejunal crypt in C3H/He and Chk2(-/-) mice. The estimated RBEs of the NCCPTC at the middle of the SOBP were 1.10 and 1.05 in the presence and absence of CHK2, respectively. The doses that reduced the number of regenerated crypt per jejunal circumference to 20 (D(20)) in C3H/He mice were 14.8 Gy (95% confidence interval [CI], 13.7-15.9) for X-rays and 13.5 Gy (95% CI, 14.5-15.5) for protons. By contrast, the doses of D(20) in Chk2(-/-) mice were 15.7 Gy (95% CI, 15.0-16.4) and 14.9 Gy (95% CI, 14.0-15.8) for X-rays and protons, respectively. The RBE of the NCCPTC is clearly within the range of RBEs determined at other facilities and is consistent with the generic RBE value of 1.10 for 150- to 250-MeV beams. The mutation of Chk2 gave rise to radioresistance but exhibited similar RBE.

Microdosimetric characteristics of proton beams from 50 keV to 200 MeV

Proton beams are of growing interest for radiation therapy due to their special physical and radiobiological properties. Microdosimetric characteristics of proton beams have strong influence on the relative biological effectiveness for each biological system. This study focused on the microdosimetric characteristics of monoenergetic protons from 50 keV to 200 MeV. Monte Carlo techniques were used to simulate track segments of protons in water. Dose mean lineal energies were derived to characterise proton beams with changing kinetic energy and changing radiation qualities at various depths and within spread-out Bragg peaks of clinic interests.

Investigation of high intensity laser proton acceleration with underdense targets

In the last few years, intense research has been conducted on laser-accelerated ion sources and their applications. Recently, experiments have shown that a gaseous target can produce proton beams with characteristics comparable to those obtained with solid targets. In underdense laser proton acceleration, volume effects dominate the acceleration, while in target normal sheath acceleration, the electric field value is directly related to the electron surface density. Using Particle-In-Cell simulations, we have studied in detail the effect of an underdense density gradient on proton acceleration with high intensity lasers. Underdense laser ion acceleration strongly depends on the length, the shape and the amplitude of the density gradient and on the laser pulse shape. The accelerated proton beam characteristics in the shock-like regime are very promising.

Application of solid-state nuclear track detectors of the CR-39/PM-355 type for measurements of energetic protons emitted from plasma produced by an ultra-intense laser

The paper reports on applications of solid-state nuclear track detectors (SSNTDs) of the CR-39/PM-355, manufactured by Pershore Moulding Ltd., for measurements of fast protons emitted from laser-produced plasma. The experiment was performed at LULI, Ecole Politechnique, on the 100 Tera-Watt laser facility. A 1.05 μm laser pulse of 350 fs duration and intensity up to 2 × 10 19 W/cm 2 irradiated a thin (1–3 μm) polystyrene (PS) or Au/PS target (PS foil covered with a 0.1–0.2 μm Au layer) along the target normal. The measurements revealed that very intense MeV proton beams can be produced under specially chosen laser-target irradiation conditions. The proton beam characteristics were measured using the TOF method (ion collectors), SSNTDs, and radiochromic films (RCFs). The SSNTDs appeared to be especially useful for the experimental analysis of more energetic protons (E p > 3 MeV). Using in the same laser shots many detector samples covered with Al foils of different thicknesses (from 15 μm up to 400 μm) it was possible to estimate energy spectra of protons emitted under various irradiation conditions. The most energetic protons (of energy up to 10 MeV) and the most intense proton beams were generated from a double-layer Au/PS target.

MO‐SAM‐BRB‐02: Proton Physics and Technology

The dose localization advantages of proton beams derive primarily from the Bragg peak in the proton stopping distribution. Therefore, the potential clinical gains expected form proton beams are based on physical, rather than biological, considerations. The rationale for proton therapy is based on the hypothesis that the superior dose distributions of proton beams will lead to increased local control; increased disease‐free survival; decreased treatment‐related morbidity; and improved quality of life. The degree to which each of these end‐points can be changed by proton therapy will depend upon the particular disease site, patient population, and other factors. In the last few years there has been a significant increase in interest in proton therapy and as a consequence, many new facilities are being planned and built. There are currently over 25 institutions worldwide treating patients with proton beams and over 55,000 patients have been treated. There are at least 25 new facilities in various stages of planning and building. We will discuss the rationale for proton therapy, the current status of proton therapy, proton physics and dosimetry, and technology for the acceleration and delivery of proton beams. We will also discuss new developments in proton therapy accelerators and treatment delivery systems. Technologies for carbon ion therapy will also be discussed. We will address issues related to the cost of proton treatments relative to the cost of photon treatments and discuss various ways in which the cost of proton therapy can be decreased.Learning Objectives:Understand1. rationale for proton therapy;2. current status of proton therapy;3. physical characteristics of proton beams;4. beam production and treatment delivery technology for proton beams;5. acceptance testing and clinical commissioning of proton therapy beams; and6. QA for proton treatments

Exploration of the potential of liquid scintillators for real‐time 3D dosimetry of intensity modulated proton beams

In this study, the authors investigated the feasibility of using a 3D liquid scintillator (LS) detector system for the verification and characterization of proton beams in real time for intensity and energy-modulated proton therapy. A plastic tank filled with liquid scintillator was irradiated with pristine proton Bragg peaks. Scintillation light produced during the irradiation was measured with a CCD camera. Acquisition rates of 20 and 10 frames per second (fps) were used to image consecutive frame sequences. These measurements were then compared to ion chamber measurements and Monte Carlo simulations. The light distribution measured from the images acquired at rates of 20 and 10 fps have standard deviations of 1.1% and 0.7%, respectively, in the plateau region of the Bragg curve. Differences were seen between the raw LS signal and the ion chamber due to the quenching effects of the LS and due to the optical properties of the imaging system. The authors showed that this effect can be accounted for and corrected by Monte Carlo simulations. The liquid scintillator detector system has a good potential for performing fast proton beam verification and characterization.

Medipix2 as a tool for proton beam characterization

Proton therapy is a technique used to deliver a highly accurate and effective dose for the treatment of a variety of tumor diseases. The possibility to have an instrument able to give online information could reduce the time necessary to characterize the proton beam. To this aim we propose a detection system for online proton beam characterization based on the Medipix2 chip. Medipix2 is a detection system based on a single event counter read-out chip, bump-bonded to silicon pixel detector. The read-out chip is a matrix of 256×256 cells, 55×55 μm 2 each. To demonstrate the capabilities of Medipix2 as a proton detector, we have used a 62 MeV flux proton beam at the CATANA beam line of the LNS-INFN laboratory. The measurements performed confirmed the good imaging performances of the Medipix2 system also for the characterization of proton beams.