MeV Carbon Beam Research Articles

SU-G-JeP1-13: Innovative Tracking Detector for Dose Monitoring in Hadron Therapy: Realization and Monte Carlo Simulations

Purpose: Development of strategies to monitor range uncertainties is necessary to improve treatment planning in Charged Particle Therapy (CPT) and fully exploit the advantages of ion beams. Our group developed (within the framework of the INSIDE project funded by the Italian research ministry) and is currently building a compact detector Dose Profiler (DP) able to backtrack charged secondary particles produced in the patient during the irradiation. Furthermore we are studying monitoring strategy exploiting charged secondary emission profiles to control the range of the ion beam. Methods: This contribution reports on the DP detector design and construction status. The detector consists of a charged secondary tracker composed of scintillating fiber layers and a LYSO calorimeter for particles energy measurement.The detector layout has been optimized using the FLUKA Monte Carlo (MC) simulation software. The simulation of a 220 MeV Carbon beam impinging on a PMMA target has been performed to study the detector response, exploiting previous secondary radiation measurements performed by our group. The emission profile of charged secondary particles was reconstructed backtracking the particles to their generation point to benchmark the DP performances. Results: The DP construction status, including the technological details will be presented. The feasibility of range monitoring with DP will be demonstrated by means of MC studies. The correlation of the charged secondary particles emission shape with the position of the Bragg peak (BP) will be shown, as well as the spatial resolution achievable on the BP position estimation (less than 3 mm) in the clinical like conditions. Conclusion: The simulation studies supported the feasibility of an accurate range monitoring technique exploiting the use of charged secondary fragments emitted during the particle therapy treatment. The DP experimental tests are foreseen in 2016, at CNAO particle therapy center in Pavia.

Defect induced magnetism in highly oriented pyrolytic graphite: bulk magnetization and 19F hyperfine interaction studies

We have made bulk and local investigations on defect induced magnetism in highly oriented pyrolytic graphite (HOPG) irradiated with a 40 MeV carbon beam. The local magnetic response of irradiated HOPG was studied by measuring the hyperfine field of recoil implanted 19F using γ-ray time differential perturbed angular distribution (TDPAD) measurements. While the bulk magnetic properties of the irradiated sample show features characteristic of room temperature ferromagnetism, the hyperfine field data reflect enhanced paramagnetism with no indication of long range magnetic ordering. The experimental studies are further supported by ab initio density functional calculations. We believe that the ferromagnetic response in irradiated HOPG arises mostly from defect induced magnetic moments of carbon atoms in the near surface region, while those deep inside the host matrix remain paramagnetic.

Dynamic screening and charge state of fast ions in plasma and solids

AbstractThis paper addresses the effect of target plasma electrons on the charge state of energetic ions, penetrating a target composed of bound as well as plasma electrons. Dynamic screening of the projectile Coulomb potential by the plasma electrons brings about a depression in the ionization energy of the ionic projectiles, as has been verified experimentally. This in turn makes the ionization cross-sections larger, while making the recombination cross-section smaller, thereby causing an increase in the ion charge state compared to the case of a gas target. The effect of the plasma environment, where the valence electrons are treated as plasma, is illustrated here for a 2 MeV carbon beam penetrating amorphous carbon targets of varying densities.

Visualization of free radical reactions in an aqueous sample irradiated by 290 MeV carbon beam

The detection of free radical reactions in a gelatin sample irradiated by a heavy-ion beam was tested using electron paramagnetic resonance (EPR) spectroscopic and MRI methods. Geometry and the amount of free radical generation in a sample are described. A reaction mixture containing glutathione and a nitroxyl radical, TEMPOL, was caked with gelatin, and then irradiated with a 290 MeV carbon beam. The amount of free radical generation in a solid sample was almost flat from the surface to the beam end, except for a small peak, the peak radioactivation profile, and then steeply decreased approaching the beam end. Total free radical reactions obtained with carbon-beam irradiation were expected to be less than one-third of X-ray irradiation, when the same dose for a deeper target was considered. Both EPR and MRI are useful tools to visualize free radical generation in samples irradiated by a heavy-ion beam. The EPR-based method is more sensitive and quantitative than the MRI-based method; however, the MRI method can achieve high spatial resolution. This study gives the rationale for a redox regulation trial using antioxidant drugs to reduce the side effects on normal tissues in carbon-beam therapy.

Surface characterization of ultra high molecular weight polyethylene modified by swift heavy ion beam bombardment

The damage processes induced by swift heavy ions (SHI), can be very different to those induced by classical low ionising particles. This is due to the high electronic stopping power of SHI. Ultra high molecular weight polyethylene (UHMWPE) was irradiated with 6.77 MeV helium and 12.5 MeV carbon beams and fluences ranging from 10 11 to 10 13 cm − 2 and 2 × 10 10 to 5 × 10 13 cm − 2 , respectively. Structural changes at the polymer near surface region were studied by means of infrared spectroscopy measurements and wear resistance tests. With FTIR spectroscopy we studied the changes in crystallinity, double bond C C, trans-vynilene and graphite formation and the evolution of methylene group as a function of fluence. The experiments have determined that exists an optimum ion fluence value, that depends on the ion mass and energy, at which the wear resistance increases of about 85% respect to the unirradiated polymer. For helium this value is 2 × 10 12 cm − 2 and for carbon 4 × 10 11 cm − 2 . At these fluence values no sign of graphite was found by FTIR studies. Using a Monte Carlo simulation program we determined that the surface area affected by the track core of the incoming ions was less than 19 and 35% for helium and carbon respectively.

Response of the FBX system to a carbon beam: its potential as a dosimeter in heavy particle radiotherapy

The FBX aqueous chemical dosimeter contains 0.2 mol m−3 ferrous ammonium sulphate, 5.0 mol m−3 benzoic acid and 0.20 mol m−3 xylenol orange in 40.0 mol m−3 sulphuric acid. The dosimeter can measure photon and electron doses in the range 0.1 to 3000 cGy in radiotherapy. The response of this dosimeter was measured for a 53.2 MeV carbon beam in the present work. Our initial result indicates that the sensitivity of the FBX system to the carbon beam as compared to cobalt-60 gamma rays is 25.5%, and thus we believe that the FBX system could be a useful dosimeter for carbon beams and similar heavy ions considered useful in radiotherapy.

Ion beam induced charge characterisation of a silicon microdosimeter using a heavy ion microprobe

An ion beam induced charge (IBIC) facility has been added to the existing capabilities of the ANSTO heavy ion microprobe and the results of the first measurements are presented. Silicon on insulator (SOI) diode arrays with microscopic junction sizes have recently been proposed as microdosimeters for hadron therapy. A 20 MeV carbon beam was used to perform IBIC imaging of a 10 μm thick SOI device.

Diagnostics of gas density gradient by swift ions

Measurements of density gradients resulting from gas ejection through a small aperture are presented. Fluorescence emission light from gas atoms excited by a fully stripped 60 MeV carbon beam was used as a diagnostic tool. The experimental results showed good agreement with the data of a hydrodynamic simulation. This work is related to the design of a high-pressure target enclosed by two fast valves in order to investigate the so-called density effect in ion stopping experiments [Nucl. Instr. and Meth. B 164–165 (2000) 139].

Calorimetric measurements of MeV ion irradiated polyvinylidene fluoride

High energy ion irradiation of semicrystalline polyvinylidene fluoride (PVDF) films changes its melting behaviour. After irradiation with 9 MeV carbon beam, differential scanning calorimetry of PVDF flims exhibits a quite complex behavior in the temperature range 20–200°C. At low ion fluence irradiation (< 1012 ions/cm2) the enthalpy of melting is constant (58.0 J/g), but a broad transition is observed before the melting temperature (160°C). At high fluences (1012–1013 ions/cm2) the enthalpy of melting decreases exponentially and the PVDF evolves into a insoluble carbon network. The crystalline polymer component decreases from 50% to 2% as suggested by the thermal analysis and the X-ray diffraction measurements.

Damage Production and Reduction of Single-Crystalline TiN Films by 1.8 MeV Carbon Beam Irradiation

By means of an in-situ Rutherford-backscattering-spectrometry (RBS) channeling technique, we have investigated creation and reduction of irradiation damage in single-crystalline TiN films induced by 1.8 MeV carbon beam. Both the effects of ion channeling and of beam heating on variation of damage level are shown briefly by successive irradiations on the order of 1017 C+/cm2 under different conditions. It is shown that the <100> aligned irradiation with a high-intensity beam repairs almost completely the damage produced by random irradiation where the sample is heated to about 450^°Cbythebeam, whereassimpleheattreatmentupto 600^°Cresultsinlessreductionofthedamage.

Track measurements on plastic sheets exposed to the CERN-SC carbon beam

ABSTRACT Track measurements on CR39 sheets exposed to the CERN-SC 86xA MeV Carbon beam are reported. The diameter of vertical tracks and the parameters of dipped tracks were measured. The p vs. REL trend is deduced. Charge discrimination for fully etched tracks is discussed.

High Resolution Spectroscopy of the Carbon K Edge in Polymers with a Doppler Tuned X-Ray Spectrometer

X-rays emitted by fast ion beams can be Doppler tuned by variation of the observation angle. With X-ray detectors collimated to a narrow acceptance angle high resolution spectroscopy of absorption structures of gaseous or solid absorbers can be performed. This novel technique seems useful in the soft X-ray region (e.g. K absorption edges of carbon to oxygen) where conventional (crystal or grating at grazing incidence) monochromators suffer from low transmission and moderate energy resolution. We studied the performance of a Doppler tuned X-ray monochromator in the carbon K region using 7.5 to 11.5 MeV carbon beams excited by gas or beam foil collisions. With X-ray detectors collimated to 1° angular acceptance the calculated monochromator band width at the carbon K edge of polymer foil absorbers becomes ?E < 0.1 eV for 7.5 MeV beam energy. The purpose of our measurements is the study of the near structure (position, width and structural details) of the carbon K edge in polymers at high resolution as a function of chemical composition.